Apple iPhone Application Development for iOS 4 Guide
जाहिरात
जाहिरात
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V I S U A L Q U I C K S t A r t G U I D E
iPhone
Application
Development for ioS 4
Duncan campbell
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Peachpit Press
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Visual QuickStart Guide
iPhone Application Development for iOS 4
Duncan Campbell
Peachpit Press
1249 Eighth Street
Berkeley, CA 94710
510/524-2178
510/524-2221 (fax)
Find us on the Web at www.peachpit.com.
To report errors, please send a note to [email protected].
Peachpit Press is a division of Pearson Education.
Copyright © 2011 by Duncan Campbell
Editor: Whitney Walker and Cliff Colby
Production Coordinator: Danielle Foster
Copyeditor/proofreader: Kim Wimpsett
Technical Editor: James Sugrue
Compositor: Danielle Foster
Indexer: Valerie Perry
Cover Design: RHDG/Riezebos
Holzbaur. Peachpit Press
Logo Design: MINE™ www.minesf.com
Interior Design: Peachpit Press
Notice of Rights
All rights reserved. No part of this book may be reproduced or transmitted in any form by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. For information on getting permission for reprints and excerpts, contact [email protected].
Notice of Liability
The information in this book is distributed on an “As Is” basis, without warranty. While every precaution has been taken in the preparation of the book, neither the author nor
Peachpit shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indirectly by the instructions contained in this book or by the computer software and hardware products described in it.
Trademarks
Visual QuickStart Guide is a registered of Peachpit Press, a division of Pearson
Education. Any other product names used in this book may be trademarks of their respective owners.
Apple, Cocoa, Cocoa Touch, Dashcode, iPhone, iPod touch, Safari, and Xcode are trademarks of Apple Inc. registered in the U.S. and other countries.
Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and
Peachpit was aware of a trademark claim, the designations appear as requested by the owner of the trademark. All other product names and services identified throughout this book are used in editorial fashion only and for the benefit of such companies with no intention of infringement of the trademark. No such use, or the use of any trade name, is intended to convey endorsement or other affiliation with this book.
ISBN-13: 978-0-321-71968-3
ISBN-10: 0-321-71968-9
9 8 7 6 5 4 3 2 1
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Dedication
For my son, Hamish.
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Acknowledgments
Thanks to Whitney Walker, Clifford Colby, Kim Wimpsett, Danielle Foster,
Valerie Perry , and everyone else at Peachpit Press who worked so hard to make this book happen.
Thanks to James Sugrue for his technical-editing expertise.
A big thank-you to my good friend Kane Nickolichuck who all those years ago pestered me relentlessly into buying my first Macintosh computer.
Cuddles and pets to my dog, Kip, for again keeping me company during the cold (yes, even in Australia!) winter evenings I spent working on this book.
Finally, the biggest thanks go to my wife, Sarah, for single-handedly looking after our newborn son while I spent the evenings locked away in my office each night.
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Contents at a Glance
Introduction
. . . . . . . . . . . . . . . . . . . . . . . . . xv
Chapter 1
Objective-c and cocoa
. . . . . . . . . . . . . . . . . .
1
Chapter 2
The iphone Developer’s Toolbox
. . . . . . . . . . .
41
Chapter 3
common Tasks
. . . . . . . . . . . . . . . . . . . . . . .
83
Chapter 4
iphone user Interface elements
. . . . . . . . . . .
111
Chapter 5
Tabs and Tables
. . . . . . . . . . . . . . . . . . . . .
181
Chapter 6
Files and networking
. . . . . . . . . . . . . . . . . .
233
Chapter 7
Touches, Shakes, and Orientation
. . . . . . . . . .
279
Chapter 8
location and mapping
. . . . . . . . . . . . . . . . .
311
Chapter 9
multimedia
. . . . . . . . . . . . . . . . . . . . . . . .
349
Chapter 10 contacts, calendars, e-mail, and SmS
. . . . . . .
405
Chapter 11 multitasking
. . . . . . . . . . . . . . . . . . . . . . . .
455
Index 469
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Table of Contents
Introduction
. . . . . . . . . . . . . . . . . . . . . . . . . . xv
Chapter 1
Objective-C and Cocoa
. . . . . . . . . . . . . . . . . .
1
Frameworks . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Creating objects . . . . . . . . . . . . . . . . . . . . . . 7
Properties . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Memory Management . . . . . . . . . . . . . . . . . . . 10
Autorelease pools . . . . . . . . . . . . . . . . . . . . . 11
Commonly Used Classes . . . . . . . . . . . . . . . . . . .14
Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Dates and times . . . . . . . . . . . . . . . . . . . . . . 20
Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Dictionaries . . . . . . . . . . . . . . . . . . . . . . . . 27
Notifications . . . . . . . . . . . . . . . . . . . . . . . . 30
Timers . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Design Patterns . . . . . . . . . . . . . . . . . . . . . . . 35
Model View Controller . . . . . . . . . . . . . . . . . . 35
Delegate . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Target-Action . . . . . . . . . . . . . . . . . . . . . . . 37
Categories . . . . . . . . . . . . . . . . . . . . . . . . . 37
Singletons . . . . . . . . . . . . . . . . . . . . . . . . . 39
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Chapter 2
The iPhone Developer’s Toolbox
41
About the Xcode IDE . . . . . . . . . . . . . . . . . . . . 42
About the Groups & Files pane . . . . . . . . . . . . . 44
Targets . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
About the toolbar . . . . . . . . . . . . . . . . . . . . . 48
About the details pane . . . . . . . . . . . . . . . . . . 49
About the editor pane . . . . . . . . . . . . . . . . . . 50
Gutter and focus ribbon . . . . . . . . . . . . . . . . . 52
Find-and-replace operations . . . . . . . . . . . . . . 53
Bookmarks. . . . . . . . . . . . . . . . . . . . . . . . . 53
Jump-to-definition and help . . . . . . . . . . . . . . . 53
Code completion . . . . . . . . . . . . . . . . . . . . . 54
About the navigation bar. . . . . . . . . . . . . . . . . 55
Creating new files. . . . . . . . . . . . . . . . . . . . . 57
Building and running your application . . . . . . . . . 58
Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . 59
About the iPhone Simulator . . . . . . . . . . . . . . . . 61
About Interface Builder . . . . . . . . . . . . . . . . . . . 64
About the document window . . . . . . . . . . . . . . 65
About the Library window . . . . . . . . . . . . . . . . 67
About the inspector window. . . . . . . . . . . . . . . 67
About the Documentation . . . . . . . . . . . . . . . . . 78
The Xcode Organizer . . . . . . . . . . . . . . . . . . . . 79
Projects & Sources . . . . . . . . . . . . . . . . . . . . 80
Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . 80
iPhone Development . . . . . . . . . . . . . . . . . . . 81
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Chapter 3
Common Tasks
. . . . . . . . . . . . . . . . . . . . . . . .
83
Application Startup and Configuration . . . . . . . . . . 84
Using the application delegate . . . . . . . . . . . . . 84
Understanding application settings . . . . . . . . . . 87
Working with user preferences . . . . . . . . . . . . . 87
Application preferences . . . . . . . . . . . . . . . . . 90
Adding controls . . . . . . . . . . . . . . . . . . . . . . 92
Localization. . . . . . . . . . . . . . . . . . . . . . . . . . 94
Accessibility . . . . . . . . . . . . . . . . . . . . . . . . . 98
Making your applications accessible . . . . . . . . . . 99
Accessibility attributes . . . . . . . . . . . . . . . . . . 101
Interapp Communication . . . . . . . . . . . . . . . . . . 103
Sharing information between applications. . . . . . .105
Using the pasteboard . . . . . . . . . . . . . . . . . .109
Chapter 4
iPhone User Interface Elements
111
Views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Bounds . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Animation . . . . . . . . . . . . . . . . . . . . . . . . . 115
Autosizing . . . . . . . . . . . . . . . . . . . . . . . . . 117
Custom drawing. . . . . . . . . . . . . . . . . . . . . . 118
Transforms . . . . . . . . . . . . . . . . . . . . . . . . . 123
Image Views . . . . . . . . . . . . . . . . . . . . . . . . . 126
Animating images. . . . . . . . . . . . . . . . . . . . . 127
Scrolling . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
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Zoom . . . . . . . . . . . . . . . . . . . . . . . . . . . .130
Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Progress and Activity Indicators . . . . . . . . . . . . . . 139
Indicating progress . . . . . . . . . . . . . . . . . . . . 139
Showing activity. . . . . . . . . . . . . . . . . . . . . .140
Alerts and Actions . . . . . . . . . . . . . . . . . . . . . 142
Alerting users . . . . . . . . . . . . . . . . . . . . . . . 142
Confirming an action . . . . . . . . . . . . . . . . . . . 144
Picker Views . . . . . . . . . . . . . . . . . . . . . . . . . 146
Toolbars . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Toolbar items . . . . . . . . . . . . . . . . . . . . . . . 153
Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .156
To use keyboards: . . . . . . . . . . . . . . . . . . . . 157
Restricting content . . . . . . . . . . . . . . . . . . . . 159
Text views . . . . . . . . . . . . . . . . . . . . . . . . .160
Data detectors . . . . . . . . . . . . . . . . . . . . . . 161
Hiding the keyboard . . . . . . . . . . . . . . . . . . . 161
Scrolling the interface . . . . . . . . . . . . . . . . . .162
Web Views . . . . . . . . . . . . . . . . . . . . . . . . . . 164
Running JavaScript . . . . . . . . . . . . . . . . . . . . 167
Loading local content and handling hyperlinks . . . .168
Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
Buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
Switches . . . . . . . . . . . . . . . . . . . . . . . . . . 172
Sliders . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
Segmented controls . . . . . . . . . . . . . . . . . . . 177
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Chapter 5
Tabs and Tables
. . . . . . . . . . . . . . . . . . . . . .
181
View Controllers . . . . . . . . . . . . . . . . . . . . . . . 182
Presenting views . . . . . . . . . . . . . . . . . . . . . 183
Responding to changes in orientation . . . . . . . . . 184
Displaying modal views . . . . . . . . . . . . . . . . .189
Handling low-memory conditions. . . . . . . . . . . . 193
Tab Views . . . . . . . . . . . . . . . . . . . . . . . . . . 194
Adding graphics and titles to tabs . . . . . . . . . . .196
Table Views . . . . . . . . . . . . . . . . . . . . . . . . 200
Grouping rows into sections and styles . . . . . . . 204
Editing and searching table views . . . . . . . . . . .210
Drilling down in table views . . . . . . . . . . . . . . . 217
Creating custom cells. . . . . . . . . . . . . . . . . . 223
Chapter 6
Files and Networking
. . . . . . . . . . . . . . . . . .
233
Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
The file system . . . . . . . . . . . . . . . . . . . . . 236
Common directories . . . . . . . . . . . . . . . . . . 237
Working with files . . . . . . . . . . . . . . . . . . . . 239
Previewing documents . . . . . . . . . . . . . . . . . 244
Networking. . . . . . . . . . . . . . . . . . . . . . . . . 248
Retrieving content from web pages. . . . . . . . . . 248
Parsing XML . . . . . . . . . . . . . . . . . . . . . . . 254
Sending data to Web pages . . . . . . . . . . . . . . 262
Responding to HTTP Authentication . . . . . . . . . 266
Creating peer-to-peer applications . . . . . . . . . . . 271
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Chapter 7
Touches, Shakes, and Orientation
279
Touch . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
Adding tapping support . . . . . . . . . . . . . . . . 285
Adding long-touch support . . . . . . . . . . . . . . 288
Multi-Touch Gestures . . . . . . . . . . . . . . . . . . . 292
The iPhone Accelerometer . . . . . . . . . . . . . . . . 298
Detecting shakes . . . . . . . . . . . . . . . . . . . . 298
Determining orientation . . . . . . . . . . . . . . . . 299
Redrawing the interface when the orientation changes . . . . . . . . . . . . . . . . . 303
Responding to the accelerometer . . . . . . . . . . 307
Chapter 8
Location and Mapping
. . . . . . . . . . . . . . . . . .
311
About Core Location . . . . . . . . . . . . . . . . . . . . 312
Handling location updates . . . . . . . . . . . . . . . . 314
Testing outside the simulator . . . . . . . . . . . . . . 315
Increasing the accuracy . . . . . . . . . . . . . . . . . 317
Adding a timeout . . . . . . . . . . . . . . . . . . . . . 318
Accessing the compass . . . . . . . . . . . . . . . . 323
About Map Kit . . . . . . . . . . . . . . . . . . . . . . . 325
Map Overlays . . . . . . . . . . . . . . . . . . . . . . 329
Adding annotations. . . . . . . . . . . . . . . . . . . 333
Adding reverse geocoding . . . . . . . . . . . . . . 338
Putting It All Together . . . . . . . . . . . . . . . . . . . . 341
Chapter 9
Multimedia
. . . . . . . . . . . . . . . . . . . . . . . . .
349
Playing Audio . . . . . . . . . . . . . . . . . . . . . . . 350
Providing more control . . . . . . . . . . . . . . . . . 352
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Responding to audio events . . . . . . . . . . . . . . 356
Playing audio in the background . . . . . . . . . . . 358
Controlling audio from the background . . . . . . . . 361
Recording Audio. . . . . . . . . . . . . . . . . . . . . . 366
Using the iPhone’s Camera. . . . . . . . . . . . . . . . . 371
Taking photos and video . . . . . . . . . . . . . . . . 375
Playing Video . . . . . . . . . . . . . . . . . . . . . . . . 381
To gain more control over movie playback . . . . . 386
Using the iPod Library . . . . . . . . . . . . . . . . . . 392
Accessing media items . . . . . . . . . . . . . . . . . 392
Accessing media collections . . . . . . . . . . . . . 394
Using the media picker. . . . . . . . . . . . . . . . . 396
Playing media . . . . . . . . . . . . . . . . . . . . . . 398
Chapter 10 Contacts, Calendars, E-mail, and SMS
405
Working with the Address Book . . . . . . . . . . . . . 406
Group records . . . . . . . . . . . . . . . . . . . . . . . 410
Person records . . . . . . . . . . . . . . . . . . . . . . 411
Adding a User Interface . . . . . . . . . . . . . . . . . . 418
Picking people . . . . . . . . . . . . . . . . . . . . . . 418
Editing people. . . . . . . . . . . . . . . . . . . . . . . 421
The iPhone Calendar . . . . . . . . . . . . . . . . . . . 428
Events . . . . . . . . . . . . . . . . . . . . . . . . . . 430
Viewing event details. . . . . . . . . . . . . . . . . . 434
Editing events . . . . . . . . . . . . . . . . . . . . . . 438
E-mail . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443
SMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
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Chapter 11 Multitasking
. . . . . . . . . . . . . . . . . . . . . . . . .
455
What Is Multitasking? . . . . . . . . . . . . . . . . . . . 456
Entering and exiting background mode . . . . . . . 457
Multitasking services . . . . . . . . . . . . . . . . . . 459
Responding to Local Notifications. . . . . . . . . . . . 466
Index 469
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introduction
Welcome to the updated version of this
Visual QuickStart Guide for iPhone application development.
A lot has happened since the last version of this book was published: In only one short year, not only have we seen the introduction of the revolutionary iPad, but we’ve also seen the all-new iPhone 4, with its gorgeous high-resolution display and powerful new hardware capabilities.
The tools for iPhone development have also had a major upgrade. iOS 4 brings with it many new application programming interfaces (APIs) that give developers even more access to the iPhone’s underlying hardware, as well as adds exciting new capabilities, such as multitasking and highdefinition (HD) video recording and editing.
At the time of this writing, more than
250,000 applications are available for download from the iTunes App Store, with more being added every minute—it’s an exciting time to be an iPhone developer!
This book is geared mainly toward new iPhone developers, but you should have some prior knowledge of a C-based language and be familiar with object-oriented
(OO) concepts. It would take a book many times this size to cover all of the iPhone software development kit (SDK), so I focus on some of the more common and interesting subjects I think you should know about when developing your own iPhone applications.
Introduction
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How to Use This Book
I find that I always learn better by example, so I have created stand-alone applications when demonstrating the concepts in the book. The aim is to give you enough information to get you started coding (and building something useful) and then point you to the relevant place in the documentation for more information.
You should be able to jump straight into a chapter and start coding without reading the prior chapters, but if you are a beginner, I recommend you read the first few chapters, which discuss the tools and language used for iPhone development.
This book is a Visual QuickStart Guide, so it’s filled with images to walk you through what you’ll see on your computer screen as you build your iPhone applications.
However, the interfaces for most of the examples are created directly in code, rather than by using Interface Builder. You might think this is unusual, since Apple has provided you with a powerful tool that makes laying out your application’s user interface quick and easy, but it’s important that you first learn what’s happening under the hood. This will make it much easier for you to figure out where to look when things aren’t working the way they should.
The source code for all the examples in this book—more than 65 projects—is available as a free download from my Web site: http://objective-d.com/iphonebook/
I strongly encourage you to check them out.
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objective-C and Cocoa
Objective-C is the language most commonly used for iOS development. It is a superset of ANSI-C, with a Smalltalk-style syntax. If you have programmed in any modern language (such as C++, Java, or even PHP), you should be able to pick up
Objective-C relatively quickly.
Cocoa is the collective name given to the frameworks provided by Apple for both
OS X and iOS development. For the purpose of this book, Cocoa will be used to mean the iOS-specific APIs.
In this chapter, you will get a brief overview of how Objective-C code is structured and how you build your own classes. You’ll then learn how memory is managed before learning about some of the more commonly used Cocoa classes. Finally, you’ll learn about some of the design patterns used throughout the Cocoa frameworks.
In This Chapter
Frameworks
Classes
Memory Management
Commonly Used Classes
Design Patterns
10
14
2
3
35
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Frameworks
iOS provides a set of frameworks for development. A framework, such as UIKit,
Core Location, Map Kit, Address Book, and Media Player, is simply a collection of classes designed to help you work with a particular technology.
Adding a framework to your projects enables you to work with the classes contained within that framework. Apple groups these frameworks into four main areas of functionality ( Table 1.1).
To add a framework to your project:
1. In the Groups & Files pane, expand the
Targets section, right-click your application target, and select Get Info.
2. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and then add the framework from the available list
A
.
3. In the header file of your class, import the framework.
Code Listing 1.1 shows an example of adding a reference to the
CoreAudio
framework to a class.
TABle 1.1 iOS Frameworks
Framework
Group Description
Cocoa Touch Frameworks for handling all the touch and event-driven programming as well as access to systemwide interface components such as the
Address Book browser, mapping, messaging, and most of the user interface components.
Media The frameworks used to play and record both audio and video as well as provide support for animation and 2D and 3D graphics.
Core Services Frameworks for accessing many of the iPhone’s lowerlevel features such as files, networking, location services, in-app purchase support, and configuration information such as network availability.
Core OS Frameworks providing access to the memory, file system, lowlevel networking, and hardware of the iPhone.
Code Listing 1.1 Referencing a framework in your code.
2 Chapter 1
A
Adding a framework to your project.
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Instance variables
Classes
As with regular C, Objective-C separates classes into two files: the header file and the implementation file. The header (.h) file is the public interface to your class; it contains declarations for the properties, instance variables, and methods available.
The header file contains the following parts:
A
.
n
The
#import
directive, much like the
C
#include
statement, allows you to include header files in your source code. However,
#import
makes sure the same file is never included more than once.
n n n
The
@interface
line declares your class name and its superclass, that is, the parent class from which your class inherits. Any protocols that the class implements are appended to the end within brackets (
<
and
>
).
Next, within the braces (
{
and
}
), you define any instance variables used by your class.
Finally, you define the methods and property declarations of your class and then close the implementation file with the
@end
directive.
#import directive Class Superclass Protocol(s)
Method declaration
A
The header file.
Property declaration
Objective-C and Cocoa
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The implementation (.m) file is where you implement the code for the methods defined in the header file. You can also implement private methods here that won’t be visible to anyone using your class.
The implementation file contains the following parts
B
: n
Again, the
#import
directive is used, this time to import the interface declaration.
n n n
The
@implementation
line begins the area where you write the code for your class.
You next use the
@synthesize
directive to generate the setter and getter methods for the properties of your class.
Notice how they can be on the same line, separated by commas.
Finally, you write your code, implementing each of the methods defined in the interface file before again closing the implementation with the
@end
directive.
#import directive
@implementation section
Synthesizing a property
Method declaration
4 Chapter 1
@end directive
B
The implementation file.
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Methods
Methods in Objective-C perform an action on an object and are surrounded by square brackets:
[myObject foo];
Here you are calling a method named
foo
on the object
myObject
. The process of calling a method is known as messaging— the message is the signature of the method including any parameters that are passed.
Objective-C is a verbose language with long and descriptive method and parameter names. The method and parameter names combine to form a phrase explaining the action of the method. A variation of camel case notation is used where the first word is usually lowercase, the first letter of each subsequent word is capitalized, and no spaces appear between words:
[myObject performSomeAction];
This would call the
performSomeAction
method of
myObject
.
When passing a value into a method, the parameter name will also often describe the data type if the type is important:
[myObject saveInteger:10];
This will call the
saveInteger
method on the
myObject
object, passing the value
10
to the first parameter.
With multiple parameters, each parameter is named and helps form the phrase describing the purpose of the method. For example, a C function to create a fraction and return the result might look like this:
fraction = MakeFraction(10,20);
Implemented as an Objective-C method, it might look like this:
fraction = [Fraction fractionWith
Numerator:10 denominator:20];
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Here you are calling the
fractionWith
Numerator:denominator:
method on
Fraction
, passing two parameters, and storing the returned value in the
fraction
variable.
The syntax for calling and defining methods is very similar. For example, you could define the previous method as follows:
-(double)fractionWithNumerator:
(int)num denominator:(int)denom;
Many classes provide what are known as class methods —instead of creating an object and then calling a method on it, you can call a method directly on the class itself.
By convention, class methods (other than
+new
and
+alloc
) usually return autoreleased objects (see the “Memory Management” section later in this chapter).
When defining class methods, you prefix the method type identifier with a plus (+) sign:
+ (MyClass *)classWithInteger:
(int)iValue
Code Listing 1.2 shows an example of some commonly used class methods.
Code Listing 1.2 Some commonly used class methods.
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Object name
Class name
Allocating memory
Initializing
C
Creating an object.
The shorthand for writing methods is to remove the datatype and parameter name from the method signature, leaving a colon (
:
) to indicate a parameter.
For example, the following method:
-(NSString *)appendString:
(NSString *) string1 toString:
(NSString *)string2
could be shortened to the following:
appendString:toString:
Creating objects
In general, to create an object in Objective-C, you do the following: n
Define the type of your object, and give it a name.
n n
Allocate memory with the
alloc
class method.
Initialize the object with an
init
method.
For example, the following
NSObject *myObject; myObject = [NSObject alloc];
[myObject init];
would normally be written as a single statement:
NSObject *myObject =
[[NSObject alloc] init];
In the breakdown of this statement, notice that there are the same number of square brackets in both examples
C
. This nesting of method calls is common in Objective-C, and you will see examples of it throughout this book.
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Many classes provide additional initializer methods allowing you to perform multiple steps in a single method call. For example, to create an
NSString
and assign it a value, you can use the following:
NSString *myString =
[[NSString alloc] initWithString:
@"some value"];
You can also use the class method:
NSString *myString = [NSString
stringWithString:@"some value"];
(
NSString
contains many of these initializer methods, which are discussed in the
“Commonly Used Classes” section later in this chapter.)
Properties
Properties provide a convenient way for you to get and set instance variables on objects without having to define or use accessor (commonly known as getter and setter ) methods.
n
For example, if you want to create a new
UIView
object, you write the following: n n
UIView *myView = [[UIView alloc]
init];
You can then set the
backgroundColor
property:
myView.backgroundColor = [UIColor
redColor];
You can also retrieve the value with the same property:
UIColor *bgColor =
myView.backgroundColor;
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Code Listing 1.3 Defining properties.
Code Listing 1.4 Synthesizing properties.
As already mentioned, properties are defined using the
@property
keyword defined in the class header (.h) file (
Code Listing 1.3).
Notice how you can define properties as being
readonly
and also how the set accessor will be implemented—as a direct assignment (which is the default), as a
retain
, or as a
copy
of the object being used for assignment.
In the class implementation (.m) file, using the
@synthesize
keyword will automatically generate the getter and setter methods (
Code Listing 1.4).
For more information on properties, refer to the “Declared Properties” section of the Objective-C 2.0 Programming Language
Guide in the developer documentation.
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Memory Management
In the “Creating objects” section earlier in this chapter, you created an object:
NSObject *myObject =
[[NSObject alloc] init];
Objective-C uses a process known as reference counting for managing memory.
When an object is created (in this example by calling the
alloc
method), it contains a reference count—also known as a retain co unt—of one. From then on, each time the object is referenced by anyone (by calling its
retain
method), the reference count increases by one. When you are finished with the object, you call its
release
method, which then decreases the reference count by one. When the reference count reaches zero, the object’s memory is freed from the system.
Objects that aren’t released after being retained will leak memory, so it’s important to make sure you always release your objects when you are finished with them. Conversely, you need to know when you should retain an object created by someone else; you don’t want an object to be released if you are still working with it, and you also don’t want to release an object you have not retained.
One useful habit when working with objects is to release them as early as possible. Consider the following code:
UILabel *myLabel = [[UILabel alloc]
init]; myLabel.text = @"some text";
[myView addSubview:myLabel];
[myLabel release];
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You first create a label, which will set its retain count to one. After setting the text, you add the label to a view. This will increase the retain count to two (the view calls
retain
on the label when it is added as a subview). You no longer need the label (the view now owns it), so you then release it on the next line. You can now safely forget about managing memory for the label—you balanced your
retain
/
release
calls, and the view will release its subviews (and therefore the label) by itself.
This pattern of releasing an object as soon as you are done with it (rather than waiting until later in your code) is a good one to use and helps reduce the likelihood of memory leaks.
Autorelease pools
To make things a little easier to work with,
Objective-C provides an autorelease pool.
Consider the following example:
-(NSString *)makeUserName
{
NSString *name = [[NSString alloc]
initWithString:@"new name"]; return name;
}
Here you have created a new string and are returning it from a method. Unfortunately, someone using this method has no way of knowing that they are supposed to call
release
on the string being returned, and therefore you’d have a memory leak.
You obviously can’t call
release
inside the method because this would set the retain count to zero and you would have nothing to return.
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The solution to this situation is to use an autorelease pool:
-(NSString *)makeUserName
{
NSString *name = [[NSString alloc]
initWithString:@"new name"]; return [name autorelease];
}
Objects created in the autorelease pool do not need to have the
release
method explicitly called but instead will release themselves at some point in the future— typically when the autorelease pool itself is released.
The disadvantage here, of course, is that while an object exists, it’s using memory.
If you create a lot of autoreleased objects, you will use up more memory, which may have a detrimental effect on your application’s performance. Because of the limited memory resources on the iPhone, it’s a good idea to manually manage memory yourself (using
retain
/
release
) whenever possible.
Objects created by calling a class method will generally return an autoreleased object. For example, the following:
UIButton *myButton = [UIButton
buttonWithType:UIButtonTypeRounded
Rect];
returns an autoreleased object that you don’t need to (and should not) release.
Of course, you can still call
retain
and
release
on autoreleased objects if you like, which might be important if you want to hold on to an object. Just make sure you never call
release
without first calling
retain
. Doing so will cause an error and likely crash your application.
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Code Listing 1.5 Using an autorelease pool.
Remember this basic rule of thumb: Any time you call the
alloc
,
copy
, or
retain
methods on an object, you must at some point later call the
release
method.
If you are creating a lot of autoreleased objects (for example, within a loop), it can often help to create your own autorelease pool at the start of your loop and then free it manually at the end. This gives you the best of both worlds: You don’t have to worry about leaking memory with manually created objects, and you can keep your memory usage under control more efficiently by manually releasing the objects in your own pool.
Code Listing 1.5 shows an example of creating and using your own autorelease pool.
You may have noticed in the first example that you didn’t have to create an autorelease pool. This is because all iOS applications have a global autorelease pool created within the main.m file (the entry point for all iOS applications).
In most cases, the Cocoa Touch frameworks use a naming convention to help you decide when you need to release objects: If the method name starts with the word when you are finished with the object.
alloc , new , or copy , then you should call release
For more information on memory management, refer to the Memory Management
Programming Guide for Cocoa in the developer documentation.
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Commonly Used
Classes
Of the hundreds of classes available in the Cocoa Touch frameworks, you will use a couple of them frequently, even in the simplest of applications.
Strings
Probably the most common class you will use will be
NSString
. An
NSString
is immutable , meaning that once you have created one, you cannot change it. If you need to alter the contents of an
NSString
, you should use the
NSMutableString
class to create a mutable string. However, it’s much more common to just create a new
NSString
with the new contents.
n
Of the many ways to create an
NSString
, the simplest is probably the following: n
NSString *myString =
@"some string";
To create a formatted string, you could use the following code:
NSString *myString = [NSString
stringWithFormat:@"object =
%@",someObject];
Some of the more common format specifiers are
%d
for
integer
,
%f
for
double
, and
%@
for
objects
. (For a complete list of available format specifiers, refer to the “String Format Specifiers” section of the String Programming
Guide for Cocoa in the developer documentation.)
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n n n n n
If you have strings that contain only numbers, you can return numeric values by using the following:
NSString *myString = @"12345"; double doubleString = [myString
floatValue]; int intString =
[myString intValue];
Both of these methods attempt to create numeric values up to the first non-numeric character in the string, so, for example, a string of
"123abc"
would return
123
for the
intValue
method.
You can get the length of a string:
int stringLength = [myString
length];
To compare two strings, you can use the following:
BOOL areEqual = [string1
isEqualToString:string2]
This will return
TRUE
if all the characters in both strings are exactly equal.
To perform a case-insensitive comparison, you can use this:
BOOL areEqual = ([string1
caseInsensitiveCompare:string2]
== NSOrderedSame);
You can also convert the case of a string:
NSString *myString = "abcdef";
NSString *upper = [myString
uppercaseString];
NSString *lower = [myString
lowercaseString];
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n n
You can easily trim a string of unwanted characters. For example, to remove all whitespace from a string, you could use this:
NSString *myString = @" one two
three ";
NSString *trimmed =
[myString string
ByTrimmingCharactersInSet:
[NSCharacterSet whitespace
CharacterSet]];
This will give you the string
"one two three"
.
You can create substrings from existing strings in several ways: n
For example, to create a new string with the contents
"one"
from this string:
NSString *numberString = @"one
two three";
you can use the following code:
NSString *aString = [numberString
substringToIndex:3];
You can use this:
NSRange range = NSMakeRange(4,3);
NSString *aString = [numberString
substringWithRange:range];
n to create a new string with the contents
"two"
.
Finally, you can use the following:
NSString *aString = [numberString
substringFromIndex:8];
to create a new string with the contents
"three"
.
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n n n n n
You can also create an array containing these three substrings as elements
(using the space character as a delimiter) by using this:
NSArray *arr = [numberString
componentsSeparatedByString:
@" "];
This will give you the array
{"one","two","three"}
.
To replace substrings in your strings, you can use the following:
NSString *aString = [numberString
stringByReplacingOccurrencesOf
String:@"three" withString:
@"four"];
This will give you the string
"one two four"
.
You can search for a substring within a string:
NSRange foundRange =
[numberString
rangeOfString:@"two"];
This will return the range
{4,3}
(indicating a match was found at position 4 with a length of 3).
You can determine whether a string contains a substring:
BOOL found = ([numberString
rangeOfString:@"two"].location !=
NSNotFound);
You can combine strings:
NSString *string1 = @"one";
NSString *string2 = [string1
stringByAppendingString:
@" two"];
This will give you the string
"one two"
.
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NSString
also contains numerous functions for dealing with files. You can read from and write to files, as well as get information such as the file path and extension.
n
For example, to read the contents of a file into a string, use the following:
NSString *fileContents = [NSString
stringWithContentsOfFile:
@"myfile.txt"];
n
You can get the file extension of a file:
NSString *fileName =
@"myfile.txt";
NSString *fileExtension =
[fileName pathExtension];
You can also use an
NSString
to both read and write to a URL. n
For example, to read the contents of a
URL into your string, you can use this:
NSURL *url = [NSURL URLWithString:
@"http://google.com"];
NSString *pageContents = [NSString
stringWithContentsOfURL:url];
Code Listing 1.6 shows some commonly used string methods.
For more information on oper documentation.
NSString
, refer to the NSString Class Reference in the devel-
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Code Listing 1.6 Some commonly used string methods.
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Dates and times
You use the
NSDate
class to compare dates and calculate date and time intervals between dates.
n
You can create an
NSDate
with the current date and time:
NSDate *myDate = [NSDate date];
n n n n n
You can create an
NSDate
that represents 24 hours from now:
NSTimeInterval secondsPerDay =
24*60*60;
NSDate *tomorrow = [NSDate
dateWithTimeIntervalSinceNow:
secondsPerDay];
You can also create a date from an existing date by using the following:
NSTimeInterval secondsPerDay =
24*60*60;
NSDate *now = [NSDate date];
NSDate *yesterday = [now
addTimeInterval:-secondsPerDay];
This will create a date representing this time yesterday.
You can compare whether two dates are exactly equal:
BOOL sameDate =
[date1 isEqualToDate:date2];
Or, to get which date occurs before or after another date, you can use the following:
NSDate *earlierDate =
[date1 earlierDate:date2];
NSDate *laterDate =
[date1 laterDate:date2];
You can calculate how many seconds occurred between two dates:
NSTimeInterval
secondsBetweenDates = [date2
timeIntervalSinceDate: date1];
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n
Or you can calculate how many seconds occurred between now and a date in the future:
NSTimeInterval
secondsUntilTomorrow =
[tomorrow timeIntervalSinceNow];
By using the
NSCalendar
class, you can create
NSDate
objects more easily. n
For example, to create a date representing June 01, 2010, use the following:
NSDateComponents *comp =
[[NSDateComponents alloc] init];
n
[comp setMonth:06];
[comp setDay:01];
[comp setYear:2010];
NSCalendar *myCal =
[[NSCalendar alloc]
initWithCalendarIdentifier:
NSGregorianCalendar];
NSDate *myDate =
[myCal dateFromComponents:comp];
Similarly, to get the day, month, and year components from an existing date, you could use this:
unsigned units =
NSMonthCalendarUnit |
NSDayCalendarUnit |
NSYearCalendarUnit;
NSDate *now =[NSDate date];
NSCalendar *myCal =
[[NSCalendar alloc]
initWithCalendarIdentifier:
NSGregorianCalendar];
NSDateComponents *comp = [myCal
components:units fromDate:now];
NSInteger month = [comp month];
NSInteger day = [comp day];
NSInteger year = [comp year];
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Calendars also make it a little easier when creating dates from existing dates since you don’t have to convert everything to and from seconds. n
For example, to rewrite the previous example of creating a date representing tomorrow, use the following:
NSDate *now = [NSDate date];
NSDateComponents *comp =
[[NSDateComponents alloc] init];
[comp setDay:01];
NSCalendar *myCal =
[[NSCalendar alloc]
initWithCalendarIdentifier:
NSGregorianCalendar];
NSDate *tomorrow = [myCal
dateByAddingComponents:comp
toDate:now options:0];
NSDate
in itself is not particularly friendly when you want to present human-readable dates and times to the user. For this, you would normally use an
NSDateFormatter
.
n
To get a string representation of the current date using an
NSDateFormatter
, use the following:
NSDate *now = [NSDate date];
NSDateFormatter *formatter =
[[NSDateFormatter alloc] init];
[formatter setDateStyle:
NSDateFormatterMediumStyle];
NSString *friendlyDate =
[formatter stringFromDate:now];
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n
To get the current time, you can use the following:
NSDate *now = [NSDate date];
NSDateFormatter *formatter =
[[NSDateFormatter alloc] init];
[formatter setTimeStyle:
NSDateFormatterMediumStyle];
NSString *friendlyTime =
[formatter stringFromDate:now];
Table 1.2 shows the five predefined formatter styles.
n
Finally, you can also use the
dateFormat
property of a date formatter to manually set a style:
NSDate *now = [NSDate date];
NSDateFormatter *formatter =
[[NSDateFormatter alloc] init];
[formatter setDateFormat:
@"yyyy-mm-dd"];
NSString *friendlyDate =
[formatter stringFromDate:now];
See the “Date Formatters” section of the Data Formatting Programming Guide for
Cocoa in the developer documentation for a complete list of available format strings.
TABle 1.2 Predefined NSDateFormatter Styles
Style
NSDateFormatterNoStyle
NSDateFormatterShortStyle
NSDateFormatterMediumStyle
NSDateFormatterLongStyle
NSDateFormatterFullStyle
Description
The default style if none is specified; no output produced
A short, numeric-only style: Date: “07/14/10”; Time: “12:32pm”
An abbreviated style: Date: “Jun 14, 2010”; Time: “12:32pm”
A full-text style: Date: “Jun 14, 2010”; Time: “12:32:04pm”
The longest style: Date: “Tuesday, June 14, 2010 AD”;
Time: “12:32:42pm GMT”
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Arrays
Arrays represent an ordered collection of objects.
For creating arrays, you use the
NSArray
class. Similarly to an
NSString
, an
NSArray
is immutable; in other words, once you have created one, you cannot alter its contents.
Use the
NSMutableArray
class to create a dynamic array whose contents can be edited after creation.
n
To create an array, you can use the following:
NSString *string1 = @"one";
n n n
NSString *string2 = @"two";
NSString *string3 = @"three";
NSArray *myArray = [NSArray
arrayWithObjects:string1,
string2, string3, nil];
Notice that the list of objects being added to the array is terminated with
nil
.
You can also create an array from an existing array:
NSArray *myArray2 = [NSArray
arrayWithArray:myArray1];
You can create an array containing only part of an existing array:
NSRange range = NSMakeRange(0,2);
NSArray *subArray = [myArray
subarrayWithRange:range];
This will create an array containing the first two objects of
myArray
.
To get the length of an array, use this:
int arrayLength = [myArray count];
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n n n n n n
You can access an object at a particular position in the array:
NSString *myString = [myArray
objectAtIndex:0];
Since arrays are zero-based, this will return the first object in the array.
You can see whether an array contains an object:
NSString *string1 = @"one";
NSString *string2 = @"two";
NSArray *myArray =
[[NSArray alloc]
initWithObjects:string1,
string2, nil];
BOOL isInArray = [myArray
containsObject:string1];
You can get the position of an object in the array:
int index = [myArray
indexOfObject: string1];
You can loop through the values of an array:
for (NSString *obj in myArray) {
NSLog(@"%@",obj);
}
Or, you can loop backward through the values of an array:
for (NSString *obj in [myArray
reverseObjectEnumerator]) {
NSLog(@"%@",obj);
}
You can also sort an array of strings:
[myArray sortUsingSelector:
@selector(localizedCase
Insensitive Compare:)];
The
@selector
keyword here is the name of the method being used to perform the sort.
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An
NSMutableArray
is similar to an
NSArray
, with the added advantage of being able to modify its contents after creation.
n
You can add an object to the end of a mutable array:
NSString *string1 = @"one";
NSString *string2 = @"two";
NSMutableArray *myArray =
[[NSMutableArray alloc]
initWithObjects:string1,
string2, nil];
NString *string3 = @"three";
[myArray addObject:string3];
n or you can add an object at the beginning:
[myArray insertObject:string3
atIndex:0];
You can replace an object at a particular position in the array:
[myArray replaceObjectAtIndex:0
withObject:string2];
n n n n
You can remove an object from an array:
[myArray removeObject:string3];
Or, you can remove an object at a particular position in the array:
[myArray removeObjectAtIndex:0];
This will remove the first object.
To remove several objects from an array, you can use this:
NSRange range = NSMakeRange(0,2);
[myArray removeObjectsInRange:
range];
This will remove the first two objects.
Finally, you can remove all the objects in the array:
[myArray removeAllObjects];
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Dictionaries
An
NSDictionary
is used to store associated key-value pairs. Again, like
NSArray
,
NSDictionary
is immutable. Use the
NSMutableDictionary
class if you need to be able to alter the contents of the dictionary after creation.
Generally, each key-value pair (called an entry ) consists of an
NSString
for the key and an
NSObject
for the value. Keys must be unique within a dictionary; values do not need to be.
NSDictionary
s are used extensively throughout the Cocoa frameworks because they provide an efficient and simple way of storing information in an easily retrievable manner. For example, user defaults are stored as dictionaries, and notifications often have a
userInfo
dictionary containing additional information about the notification.
n
To create a dictionary, you can use the following:
NSArray *arr1 = [NSArray
arrayWith Objects:@"iPhone",
@"iPod",nil];
NSArray *arr2 = [NSArray
arrayWith Objects:@"iMac",
@"Mac Pro", @"Macbook",
@"Macbook Pro",nil];
NSDictionary *myDict =
[[NSDictionary alloc]
dictionaryWithObjectsAndKeys:
arr1, @"mobile", arr2,
@"computers", nil];
Notice that like an
NSArray
, you end the list of objects with
nil
when creating the dictionary.
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n n n n n n n
You can see how many elements are in an dictionary:
int dictSize = [myDictionary
count];
You can access an object in the dictionary:
NSArray *mobile = [myDict
objectForKey:@"mobile"];
Or, to retrieve the keys for an object, use the following:
NSArray *keys = [myDict
allKeysForObject:arr1];
To retrieve an array of all the values in the dictionary, use this:
NSArray *values = [myDict
allValues];
You can also enumerate through the contents just like an
NSArray
:
for (id key in myDict) {
NSLog(@"key: %@, value: %@",
key, [myDict objectForKey:
key]);
}
If your dictionary contains only property list objects (
NSData
,
NSDate
,
NSNumber
,
NSString
,
NSArray
, or
NSDictionary
), you can save it to a file:
NSString *filePath = [[[NSBundle
mainBundle] resourcePath]
stringByAppendingPathComponent:
@"dict.txt"];
BOOL success = [myDict
writeToFile: filePath
atomically:YES];
Conversely, you can populate a dictionary from a file:
NSDictionary *myDict2 =
[NSDictionary dictionaryWith
ContentsOfFile:filePath];
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By using an
NSMutableDictionary
, you can add and remove objects after creation.
n
To add an object to a mutable dictionary, you can use this:
NSArray *arr1 = [NSArray
arrayWith Objects:@"iPhone",
@"iPod",nil];
NSArray *arr2 = [NSArray
arrayWithObjects:@"iMac",
@"Mac Pro", @"Macbook",
@"Macbook Pro",nil];
NSMutableDictionary *myDict =
[[NSMutableDictionary alloc]
initWithObjectsAndKeys:arr1,
@"mobile", arr2, @"computers",
nil];
NSString *string1 = @"AppleTV";
[myDict setObject:string1
forKey:@"media"];
n n n n
You can also alter an existing object in the dictionary:
NSString @string2 = @"airport
express";
[myDict setObject:string2
forKey:@"media"];
Or, you can remove an object from the dictionary:
[myDict removeObjectForKey:
@"media"];
To remove multiple objects, use the following:
NSArray *keyArray = [NSArray
arrayWithObjects:@"mobile",
@"computers",nil];
[myDict removeObjectsForKeys:
keyArray];
Finally, to remove all objects from the dictionary, you can use the following:
[myDict removeAllObjects];
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Notifications
Notifications provide a handy way for you to pass information between objects in your application without needing a direct reference between them. They are represented by the
NSNotification
object, which contains a name, an object (often the object posting the notification), and an optional dictionary.
Notifications are posted to a notification center whose job is to forward the notification to all registered observers—objects that have requested to be told about certain notifications.
n
To register your object as an observer for a notification, you can write the following:
[[NSNotificationCenter
defaultCenter] addObserver:self
selector:@selector(doSomething:)
name:@"myNotification"
object:nil];
n n
Here you are observing a notification called “
myNotification
.”
When the notification is sent to your object
(by the notification center), a message is sent to the
doSomething:
method. By passing
nil
to the final parameter, you are saying that you want to be told about any notification named
myNotification
, no matter which object sends it. You could have optionally specified which object you wanted to observe, which might be useful in the situation where multiple notifications have the same name.
To post your own notification to send the dictionary discussed earlier, you can use this:
[[NSNotificationCenter
defaultCenter]
postNotification
Name:MY_NOTIFICATION
object:myDict];
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n
You can then access the dictionary being sent:
-(void)doSomething:(NSNotification
*)aNote {
NSDictionary *myDict = [aNote
object];
Code Listing 1.7 shows an example of both posting and receiving a notification. Note that in this example both the sending and receiving objects are in fact the same, which wouldn’t normally be the case.
Notice how the notification name has been defined as a variable (
MY_NOTIFICATION
). This is a good practice because the compiler will report a compile-time error if you mistype the notification name.
Remember to stop observing notifications by using removeObserver: when you are finished with the notification. As in the previous example, this is often done in the dealloc method.
Code Listing 1.7 Registering for, posting, and receiving a notification.
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Timers
Another common task is to have some code run based on some type of timing function. For example, you might be implementing a clock and want the display to update every minute, or you may want to present a message to a user and have it disappear after a certain amount of time.
You can use the
NSTimer
class to add this type of functionality to your applications.
Timers allow you to execute a piece of code after a given amount of time.
n
The simplest way to create a timer is by using the class method:
NSTimer *myTimer = [NSTimer
scheduledTimerWithTime
Interval:10.0 target:self
selector:@selector
(myTimerAction:)
userInfo:nil repeats:NO];
This will create a timer that calls the
myTimerAction:
method in ten seconds from now. Notice the
userInfo
parameter: This lets you pass any object you like to your timer method. Passing
NO
to the
repeats
parameter means your timer method will be called only once.
If you pass
YES
, the timer would keep repeating every ten seconds.
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n n n n
You then implement your
myTimerAction:
method:
-(void)myTimerAction:(NSTimer *)
timer
{
NSLog(@"timer fired!: %@",[timer
userInfo]);
}
The timer passes itself as a parameter to the method. Notice how you can get the
userInfo
object you added when creating the time (in this example,
nil
).
To stop a timer, you call the following:
[myTimer invalidate];
You can also create a timer that you don’t actually want to run until later:
myTimer = [[NSTimer timerWith
TimeInterval:10.0 target:self
selector:@selector
(myTimerAction:) userInfo:nil
repeats:NO] retain];
Then, when you are ready to start the timer, you use the following:
[[NSRunLoop mainRunLoop]
addTimer:myTimer forMode:
NSDefaultRunLoopMode];
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n
Another less common way of creating a timer is by using the following:
NSTimeInterval *secondsPerDay =
24*60*60;
NSDate *tomorrow = [NSDate
dateWithTimeIntervalSinceNow:
secondsPerDay]; myTimer = [[NSTimer alloc]
initWithFireDate:tomorrow
interval:10.0 target:self
selector:@selector
(myTimerAction:) userInfo:nil
repeats:YES];
This creates a timer to run tomorrow that will repeat every ten seconds.
Again, you need to call
addTimer:forMode:
to actually start the timer; however, this time you have created a timer that first fires at an exact point in time.
Code Listing 1.8 shows an example of working with a timer.
Code Listing 1.8 Using timers.
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Design Patterns
When writing applications, you may often find yourself building the same functionality or encountering similar design problems time and time again. Design patterns offer a solution to this situation by providing a set of general, reusable, tested solutions to common programming scenarios.
Design patterns are used extensively throughout the iOS frameworks. If you write an iOS application, you are using them whether or not you know it. The following are some of the more frequently used design patterns in iOS development.
Model View Controller
The Model View Controller (MVC) pattern separates an application’s data structures
(the model) from its user interface (the view), with a middle layer (the controller) providing the “glue” between the two. The controller takes input from the user (via the view), determines what action needs to be performed, and passes this to the model for processing. The controller can also act the other way: passing information from the model to the view to update the user interface.
Breaking your application into distinct components like this reduces dependencies and increases the reusability of the code.
It’s entirely possible that you could reuse the same model across multiple applications with different views and controllers.
MVC is used everywhere in the iOS frameworks. You will notice many classes with the word View or Controller in their names, and almost all the project templates create an MVC-based project.
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Delegate
The Delegate pattern is useful as an alternative to subclassing, allowing an object to define a method but assign responsibility for implementing that method to a different object (referred to as the delegate object or, more commonly, the delegate).
Delegates need not implement all (or even any) of the delegate methods for the source object. In that case, the source object’s default behavior for the method is often used.
Code Listing 1.9 shows an example of a delegate used for a
UITextField
object.
By implementing the
textFieldShould
BeginEditing:
delegate method (and in this example, returning
NO
), you can control the appearance of the keyboard.
As with MVC, delegates are frequently used throughout the iOS frameworks, and you will use them often in your application development.
Code Listing 1.9 Using a delegate.
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Code Listing 1.10 Buttons use the target-action pattern.
Target-Action
This pattern is used by most of the controls in the iPhone user interface. When creating a control, you assign the target object to send a message to, and you supply the method in that object to call when a particular action (for example, tapping a button) occurs. It is your responsibility as the developer to implement the methods for these actions.
Code Listing 1.10 shows an example of using the Target-Action pattern to handle a
UIButton
.
Categories
Like delegates, categories provide an alternative to subclassing, allowing you to add new methods to an existing class. The methods then become part of the class definition and are available to all instances
(and subclasses) of that class.
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Code Listing 1.11 and Code Listing 1.12 show an example category that adds a new method to the
UIImage
class. Notice how in both the interface and implementation definitions you use the class name, with the category name in parentheses.
Although you can name your category header and implementation files anything you like, a common convention is to use the original class name with
+xxx
appended. The
xxx
describes the additional functionality provided by the category (or, as in the example here, is a generic term indicating additional functionality).
Code Listing 1.12 The category implementation.
Code Listing 1.11 The category header.
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Code Listing 1.13 Using the
UIDevice
singleton.
Singletons
You can think of a singleton as a global object. There will only ever be one, and it is available to all the classes in your application. Although this pattern is not frequently used, you will use several important singletons when developing iOS applications such as
UIApplication
and
UIDevice
.
Code Listing 1.13 shows an example of using the
UIDevice
singleton to check the battery level of an iPhone.
For more information on the design patterns used in iOS development, refer to the “Cocoa Design Patterns” section in the
Cocoa Fundamentals Guide in the developer documentation.
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The iPhone
Developer’s Toolbox
Before you can begin building your own applications for the iPhone, you’ll need to register with Apple as a developer and download the iOS software development kit (SDK). Luckily, both of these steps are easy and completely free—simply visit http://developer.apple.com
. You’ll also find a wealth of information regarding iPhone development, including documentation, tutorials, videos, sample code, and more.
The iOS SDK includes the Xcode integrated development environment (IDE), iPhone Simulator, Interface Builder, documentation, and a number of other tools you’ll need when developing iPhone applications.
In This Chapter
About the Xcode IDE
About the iPhone Simulator
About Interface Builder
About the Documentation
The Xcode Organizer
42
61
64
78
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About the Xcode IDe
This chapter presents a whirlwind tour of some of the tools you’ll use on a daily basis as an iPhone developer. You can find more information on the Apple Developer Connection Web site (http://developer.apple.com).
Xcode is part of a suite of development tools used for creating iPhone, iPod touch, iPad, and OS X applications. Among others, there are tools for user-interface design, source-code editing and management, integrated debugging, and performance analysis.
When you first launch Xcode, you are presented with a welcome screen
A
. This screen contains lots of useful information such as links to videos, sample code, RSS feeds, tips and tricks, and documentation.
It’s well worth your time to go through the tutorials and code and subscribe to the mailing lists and RSS feeds. If you have a question, it’s very unlikely you are the first to ask, and the searchable mailing list archives are an excellent place to look for an answer.
If you close this window and choose File >
New Project, you’ll see the Xcode New
Project window where you can choose a template for your project
B
. As an iPhone developer, you are interested only in the iPhone OS section of the list.
A
The Xcode welcome screen.
B
Choosing a project template.
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C
Saving your project.
When you select a template type, you’ll see a short summary of its use. Xcode automatically creates boilerplate interface
(.xib) and code (.h/.m) files for each template. Again, you should spend some time going through each of these templates and familiarizing yourself with them. Most of the examples in this book use the View-based
Application template, which is a good one for general use.
Now you’ll create a new project and walk through the main parts of the Xcode interface.
To create a new project:
1. Start Xcode.
2. Choose File > New Project.
3. Select the View-based Application template, and save your project as helloWorld
C
.
Xcode now displays your project in a single window with a number of panes
D
.
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D
The main Xcode window.
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About the Groups & Files pane
The Groups & Files pane shows the contents and configuration of your project, categorized into either static or smart groups
E
.
Static groups provide a convenient way for you to categorize files and folders. They are used only in the context of an Xcode project, and they do not necessarily reflect any physical folder structure in the file system.
You can create as many static groups as you like, and they can be nested within each other.
By default, Xcode creates the groups described in Table 2.1.
The <app>-Info.plist file contains configuration settings about your application.
Table 2.2 lists some of the settings automatically created with your application.
As a general rule, most developers create their own groups for their code and use the existing Resources folder for files such as graphics, but you can place your code and
E
The Xcode Groups & Files pane.
TABle 2.1 Static groups
Group
Classes
Description
Contains the header and implementation files for the classes that are automatically generated for the application type that you selected when you created your project.
Other Sources Contains the prefix header file used by Xcode to reduce compile time and contains the main.m file that is the entry point to your application. (It’s generally advised that you not touch either of these files unless you know what you are doing.)
Resources Contains the XIB files containing your application’s user interface and contains the
<app>-Info.plist file, which specifies your application’s settings.
Frameworks Contains the frameworks used by your application (these may differ based on the template type you chose when creating your project).
Products Contains the compiled binary representing your application. This is the file that is installed on the simulator and uploaded to Apple for sale in the iTunes App Store. You may notice that if you’ve never compiled your application or you’ve never performed a clean (from the
Build toolbar), this file will appear with red text. This is how Xcode displays missing files.
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F
G
Adding a new group.
The default smart groups.
TABle 2.2 <app>-Info.plist properties
Property
CFBundleDisplayName
CFBundleIconFile
CFBundleIdentifier
CFBundleVersion
LSRequiresIPhoneOS
NSMainNibFile
Description
The name your app shows on the iPhone.
The PNG file containing your application icon.
The identifier you set up on the iPhone
Developer Program
Portal section of the Developer
Connection Web site to uniquely identify your application.
The current version of your application.
You will update this each time you submit your application to the
App Store.
Set to
true
if your application can only run on iPhone OS
The initial user interface XIB file, loaded by the call to
UIApplicationMain()
in the main.m file.
other project files in any of these groups, move them around, rename or delete them, or create your own. The groups are simply there to make your life as a developer easier when managing your application’s code and assets.
To create a new group:
1. Right-click the topmost item in the Groups
& Files pane (in this case helloWorld), and choose Add > New Group.
2. Name your group My Files
F
.
Smart groups are the second type of group
G
. Again, Xcode automatically creates a number of these groups to categorize various types of information ( Table 2.3).
TABle 2.3 Smart groups
Group
Targets
Executables
Errors and
Warnings
Find Results
Bookmarks
SCM
Description
You will have an entry here for each of your project targets (defined in the next section).
Contains all of the executables for your project.
Each error or warning your application generates on compile will be listed here.
This shows the history of any projectwide searches you have performed.
This shows all bookmarks for your project.
If you are using source-code management, this group shows you the status of any files that may have changed under source control.
Currently Xcode has support for the CVS, Perforce, and
SVN source control systems.
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Targets
A target is a set of instructions for building a product. These instructions might include such information as which source files to compile or resources to copy, as well as any special instructions for processing them. In most cases, you will be working only with the default target created with your project.
If you expand the helloWorld target
H
, you’ll see folders representing the main steps Xcode will perform when building the sample application: copying files into the application bundle, compiling the source code, and linking against the frameworks in the project.
Right-click the helloWorld target, and choose Get Info (Command+I) to open the
Target Info dialog box
I
. It has five tabs.
n
General—Shows you the libraries and frameworks currently linked against your project, as well as any other dependencies (such as external projects) you may have. You can add other frameworks or linked libraries (such as
SQLite) using the Add (+) button in the bottom-left corner
J
.
n
Build—Shows you the settings Xcode will use when building your product
K
.
They are grouped into configurations, providing a handy way to apply a range of settings without having to create multiple targets.
H
The project target group, expanded.
I
The Target Info dialog box.
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The project’s General tab.
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K
Build settings for project.
L
Settings for the XIB Files smart group.
n n n
By default, Xcode creates Debug and
Release configurations. The Debug configuration is what you will generally use in your day-to-day development, allowing you to interact with the application using the debugger, among other things. When you are ready to deploy your application to the iTunes
App Store, you would build using the
Release configuration, creating an optimized, production-ready version of your product.
Rules—Specifies how particular file types are processed when your application is compiled. For example, you could pick a certain compiler version to compile your source files.
Properties—Shows the contents of the
<app>-Info.plist file in a slightly more human-readable form than simply viewing the file itself.
Comments—Lets you add your own comments for the project. You can write anything you want here; comments will be stored with the project.
You can find a lot more information on targets and the build system in the
Xcode Build System Guide .
You may also notice the last two smart groups in the Groups & Files pane, Implementation Files and XIB Files, have the same icon. These are special groups similar to Smart Folders in OS X. If you
Control+click the XIB Files folder and choose Get Info (Command+I), you’ll be doing a simple match for all files that have the extension .xib
L
.
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To create a smart group:
1. Choose Project > New Smart Group >
Simple Regular Expression Smart Group.
2. Change the name to Images and the
Using Pattern value to \.(png|gif|jpg|tif)$.
You should now see this group at the bottom of your Groups & Files pane
M
. Any image files you add to your project will automatically be shown here.
About the toolbar
When you first launch Xcode, the default toolbar features the following options: n n n n n n
Overview—Shows you the current build settings for your application. This tells you whether you are currently building for the simulator or an actual iPhone, along with which build configuration you are using
N
.
Action—Provides a shortcut to a number of often-used actions.
Build and Go—Builds your application and installs and launches it on either the iPhone Simulator or the iPhone (depending on what you’ve chosen in the Active
SDK dialog box, which is accessible via the Overview toolbar menu).
Tasks—Allows you to cancel a build in progress.
Info—Shows additional information for any item selected in either the Groups
& Files pane or the details pane.
Search—Allows you to filter the list of items currently shown in the details pane.
When you first launch Xcode, the default toolbar is adequate
O
. However, there are a couple more items you can add to make it a little more useful. You’ll use them later in this chapter.
M
The completed smart group settings.
N
The Overview menu showing the current build settings for the application.
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To update the toolbar:
1. Control+click the toolbar, and choose
Customize Toolbar.
2. Drag the Build toolbar item that has the disclosure triangle, and drop it onto the toolbar.
3. In the same way, drag the Debugger and Editor toolbar items, and click Done to close the Customize Toolbar window.
Your toolbar is now updated
P
.
About the details pane
The details pane shows a list of files, based on what is currently selected in the Groups
& Files pane. For example, if you select multiple group, you’ll see all files for the groups
Q
.
O
The default Xcode toolbar.
P
The updated toolbar.
Q
Selecting multiple groups in the Groups & Files pane will show all files in the details pane.
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Column headers in the details pane show information such as filename, file size, build status, errors, and warnings. When the helloWorld project has a build error, Xcode highlights the error in the editor pane
R
.
Selecting a file in the details pane opens the file in the editor pane below. Doubleclicking or pressing Enter when a file is selected causes it to open in its own editor window.
Depending on the file type, it may display as an image or as a property list
S
. Readonly files such as frameworks do not show in the editor pane at all.
To see more details about a file, such as its physical location, click the Info toolbar button (or press Command+I).
When you select a property list file, it defaults to displaying as a table of key-value pairs. Although this is useful most of the time, you sometimes want to edit the raw source of the file. You can accomplish this by
Control+clicking the property list file in the details pane and choosing Open As.
About the editor pane
Xcode contains all the features you would expect from a modern editor, such as syntax highlighting, code completion, smart indenting, code folding, multidocument support, unlimited undo and redo, and more.
You can expand the amount of space you have for editing code by clicking the Editor toolbar icon you added earlier
(or by pressing Shift+Command+E). This causes the details pane to collapse and provides the full window height for the editor
T
.
R
Xcode shows detailed information about errors in code.
S
Xcode displays property lists as a table of keys and values.
T
Collapse the details pane to increase the area for your code.
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U
The editor pane with all other panes collapsed.
V
Quickly find and open files in your projects.
Taking this further, if you also hold down the
Option key (Option+Shift+Command+E), the
Groups & Files pane collapses as well
U
.
Finally, pressing Option+Command+O causes the current file to open in its own window.
To quickly open files in your project from the keyboard, you can use the Open Quickly dialog box (Shift+Command+D), which lets you start typing to find the filename. Positioning your pointer on a file, variable, or method before invoking this dialog box will default to showing the file containing that variable, method, or name
V
.
When creating new files in Xcode, the default behavior is to put the file in whichever static group is currently selected. If no group is selected, the file is added at the top level of the list—you can of course move your files around within groups at any time after you’ve added them to the project.
When adding existing files to your projects, you will have the option to copy the items into your project’s folder and choose what reference type to use
W
. It’s advisable to always select this option and to use the default reference type. If you were to move your project to a different location or machine at a later date, the file might not exist in the same location. In this situation,
Xcode would indicate this by displaying the file in red.
W
Adding external files to your projects.
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Gutter and focus ribbon
The gutter on the left shows line numbers, breakpoints, errors, and warnings (you may have to enable line numbers in the Xcode preferences)
X
. Clicking in the gutter will add a breakpoint at the current line. Clicking the breakpoint will change it to a light blue color, indicating it has been disabled.
To remove the breakpoint, you can either drag the breakpoint off the ribbon or
Control+click and choose “Remove breakpoint” (you can also press Command+\ to toggle breakpoints).
Next to the gutter is the focus ribbon.
Moving your pointer over a shaded area in the ribbon causes the code for that scope to be highlighted and the rest of your code to be dimmed
Y
.
Clicking in the shaded scope area of the focus ribbon makes your code fold and unfold, replacing your code with a small graphic ellipsis symbol
Z
. Double-clicking the icon unfolds the code.
This is a great way for you to hide code you’ll never read (such as comments at the header of a file) or that you may not change often.
You can also control code folding from the keyboard: Pressing Control+Command+left arrow or Control+Command+right arrow causes the current scope to fold or unfold.
Pressing Control+Command+up arrow or
Control+Command+down arrow causes all methods in the current file to fold or unfold.
If you like the scope highlighting effect, you can enable it all the time by choosing
Focus Follows Selection from the View >
Code-Folding menu. This is a great way to see your code in functional groups.
X
The Xcode editor pane with a breakpoint set.
Y
Highlighting scope makes code more readable.
Z
Collapsed code is represented by an ellipsis in the editor window.
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Searching for text within the current file.
Searching within the entire project.
You can quickly comment or uncomment your code by highlighting a block and pressing
Command+/.
Find-and-replace operations
Pressing Command+F opens the Single
File Find dialog box , allowing you to perform find-and-replace operations within the current file. Pressing Command+G and
Shift+Command+G navigates forward and backward through matches.
Pressing Shift+Command+F brings up the more powerful Project Find window , which allows you to search through all files within your project and even into frameworks and other projects. Remember that Project Find history is also available in the Find Results smart group in the
Groups & Files pane.
Bookmarks
Often you’ll want to return to a particular line within your source code. Pressing
Command+D allows you to bookmark a location. You can then access those bookmarks from the Bookmarks pop-up menu as well as the Bookmarks smart group in the Groups & Files pane.
Jump-to-definition and help
If you Command+double-click any symbol, variable, or method within your code, Xcode opens the relevant file and highlights the definition of that symbol. If more than one definition exists, you’ll be presented with a pop-up menu of all the files containing the symbol, allowing you to select which to open. This is extremely useful when browsing the Cocoa header files because you can quickly, for example, jump to the header definition of a class to see its properties and methods.
Similarly, if you Option+double-click, Xcode opens the documentation for that symbol.
Again, this is a very quick and easy way of looking up how to use a particular function, class, or method.
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Code completion
Objective-C often has very long method names, and the Cocoa frameworks are huge, making it very difficult to remember what to type. This is where code completion comes in: Begin typing a method name, and Xcode will suggest the method it thinks you want based on the context of your code .
The more you type, the more accurate
Xcode’s match will become. When the right choice appears, press Tab to have Xcode complete the code for you.
Optionally, if you press the Esc (Escape) key, you will be presented with a list of all matches for the current completion .
You can then navigate the list with the up and down arrow keys and press Enter to choose a match.
If your completion has multiple parameters,
Xcode will automatically highlight the first parameter. Once you enter a parameter, you can press Control+/ to move to the next one. Similarly, Shift+Control+/ moves you backward in the parameter list.
Code completion is enabled in the preferences menu, or you can manually invoke it by pressing the Esc key. You can even position the pointer over some existing, already completed code and then press Esc to see a list of other possible completions.
The button at the bottom right of the completion list allows you to toggle the sorting of the list between alphabetical and “bestguess” results .
Code completion shows the parameters of your methods as you type.
Xcode presents multiple completion matches as a list.
Toggle the way completions are presented.
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Navigation arrows
File-history menu Function menu
Arrows in the navigation bar and the filehistory menu let you navigate through the editor pane’s history.
You can enhance the function menu to show developer comments.
About the navigation bar
Above the content pane is the navigation bar .
The arrows on the left of the bar allow you to navigate forward and backward through your editor pane history. You can also get at the same information by clicking the filehistory menu (Control+1 on the keyboard).
The function menu (Control+2 on the keyboard) shows a summary of all the class, function, method, and type declarations and definitions for the current file. Selecting one will jump to that point in your code.
There are also a number of special keywords you can put in your code to create marker labels in this menu. For example, putting the following before the
dealloc
method of a class
#pragma mark some comment here
would result in the function menu looking something like .
You can also break up the menu by adding separator labels, such as
#pragma mark -
which results in something like .
There are also a number of special comment types:
//???: a question
//!!!: something important
//MARK: this is a mark
//TODO: a to-do item
//FIXME: something needs fixing
Adding breaks to the function menu makes it easier to read.
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Now the code snippet contains all the special identifiers and the resulting menu .
The right side of the navigation bar contains a number of useful pop-up menus and buttons : n
Bookmarks—Gives you access to bookmarks for the current file (you can also press Control+4 on the keyboard). Recall that bookmarks for your entire project are visible in the Groups & Files pane.
n n n
Breakpoints—Allows you to jump between any breakpoints set in the current file.
Class hierarchy—Lists all the superclasses and subclasses of your current file.
Included files—Lists all the files that the current file includes or is included in.
n n
Counterpart—Allows you to jump between the implementation and header files (Option+Command+up arrow on keyboard).
Lock—Lets you set the read-only state of the current file.
You may have noticed the button at the top of the scroll bar on the right side of the editor pane. This is the handy splitview button, which lets you not only edit multiple parts of the same file at the same time but also open multiple files within an editor .
The function menu showing multiple comment styles.
Bookmarks
Class hierarchy Counterpart
Breakpoints Included files
Lock
Pop-up menus in the navigation bar.
Splitting the editor allows you to work on the application delegate with both the header and implementation file open for editing.
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Adding a new class file to the application.
Saving the new class.
The Classes folder showing the newly added classes.
When creating a new class, the “Created by” and Copyright comments at the top of the files come from the current user’s Address
Book card.
Creating new files
You create new files via the File > New File menu, which prompts Xcode to present a number of file templates for you to use during the application-creation process.
In iPhone development you’ll normally use templates from the iPhone OS section only.
Within this section are four subsections: n n
Cocoa Touch Class—Is the most common area you’ll use; it provides templates for standard Objective-C iPhone classes.
Code Signing—Allows you to create files related to signing your applications for ad hoc deployment.
n n
Resource—Provides templates for a number of resources, including Core
Data models and application settings bundles.
User Interface—Provides templates for creating the XIB files used in Interface
Builder.
Now you’ll add a custom
UIView
subclass to your application.
To add a class to your application:
1. Select Cocoa Touch Class from the left side of the template window, and select
“Objective-C class” as the file template.
Notice how UIView is selected in the
“Subclass of” drop-down menu .
2. Click Next, and save your file as myView.m. Make sure that “Also create ‘myView.h’” is selected, and click Finish .
You should see your new myView.h and myView.m files in the Classes group of the
Groups & Files pane . When you open the myView.m file, you can see that Xcode has created stub placeholders for the most common methods.
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Building and running your application
To run your application, click Build and Go in the toolbar, or press Command+R. The
Build Results window will open, displaying the status of your application target’s build
(you may have to enable this in the Building section of the Xcode preferences) .
The Build Results window lists any errors and warnings in your application. Clicking one will open an Xcode editor pane directly in the Build Results window, allowing you to fix the error without having to leave the current window. Double-clicking opens a new editor window .
Some build errors may not be immediately obvious, such as a misreferenced file in your project. By right-clicking the build details and choosing Expand All Transcripts, you can show or hide the build details .
If there are no errors in your application, the iPhone Simulator will open, install, and launch your application.
The Build Results window shows details of the project build.
The Build Results window showing an error in the code.
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The Build Transcript button lets you show or hide your build details.
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The Clean Target dialog box.
Cleaning
Each time you build your application target,
Xcode performs only the actions required to update any files that were changed since the last build.
Xcode is not perfect, however, and sometimes it doesn’t notice that a file has changed (such as when you replace an image in your project with another of the same name). In this situation, you need to perform what’s known as a clean.
To clean a target, choose Build > Clean, or press Shift+Command+K on the keyboard.
Cleaning a target removes any intermediate files created during the previous build process. The next time you build, every file will be processed .
For more details on the Xcode build system, see the “Building Products” section in the Xcode Project Management Guide.
Table 2.4 summarizes some of the common editor shortcuts.
Building for iPhone vs. iPhone Simulator
If you look at the Overview toolbar item in both Xcode and the Build Results window, you’ll notice it has a section called
Active SDK .
This is how you determine whether you are deploying your application to an actual iPhone or to the iPhone Simulator.
Although the simulator will work out of the box, in order to install your application onto an iPhone (or iPod), you must have a provisioning profile and a development certificate installed on both your Mac and your iPhone.
You can find details of what these are and how to create and install them at the iPhone Dev Center Web site
(http://developer.apple.com/iphone).
The Overview toolbar shows you whether you are building for the simulator or iPhone.
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TABle 2.4 Common keyboard shortcuts
Shortcut
Shift+Command+E
Option+Shift+Command+E
Option+Command+O
Option+left arrow
Option+right arrow
Command+left arrow
Command+right arrow
Command+up arrow
Command+down arrow
Command+L
Command+Z
Shift+Command+Z
Command+/
Command+D
Command+\
Control+Command+\
Command+F
Command+G
Shift+Command+G
Shift+Command+F
Control+1
Control+2
Control+3
Control+4
Option+Command+up arrow
Command+double-click
Shift+Command+K
Command+B
Command+R
Command+Y
Description
Collapse/expand details pane
Collapse/expand details pane and Groups & Files pane
Open current document in new window
Go to previous word (+Shift to select)
Go to next word (+Shift to select)
Go to beginning of line (+Shift to select)
Go to end of line (+Shift to select)
Go to beginning of document (+Shift to select)
Go to end of document (+Shift to select)
Go to line
Undo
Redo
Comment/uncomment selected block
Create bookmark
Add/remove breakpoint
Deactivate/reactivate all breakpoints (projectwide)
Find in current file
Go to next match
Go to previous match
Find in project
Open file-history menu
Open function menu
Open Included files menu
Open Bookmarks menu
Switch between header and implementation file
Jump to definition of current symbol
Clean current target
Build application
Build and run application
Build and debug application
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About the iPhone
Simulator
You will usually use the iPhone Simulator for the majority of your iPhone development. The simulator lets you build, run, and test iPhone applications on your computer rather than on an actual iPhone.
Although you can simulate most of the iPhone environment, the simulator can’t do a number of tasks well, and it has several important differences from the iPhone environment.
The simulator has significantly better performance than an actual iPhone.
Everything from application launch time and general UI speed to available memory are much improved on the simulator. How much better it performs will depend on the computer you are developing with, but if speed is important to your finished application, you should be testing your code on an actual iPhone as early as possible in your development cycle to get an accurate measure of its actual performance.
The simulator provides a number of functions that mimic an iPhone: n
SDK version—You can simulate your code running under multiple versions of iOS.
n n
Rotation and shakes—The simulator can be rotated left and right as well as shaken, triggering the appropriate delegate methods in your view controllers.
Home and Lock buttons—Both buttons work as they do on the iPhone.
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n n n
Memory warnings—You can trigger lowmemory warnings, which can be very useful in making sure your applications handle low-memory situations gracefully.
Toggle in-call status bar—This status bar allows you to see how your application would look with the in-call status bar active
A
.
Touch—Using the mouse, you can simulate either a single touch or, by holding the Option key, a two-finger touch. For more details on touch gestures in the simulator, see “Performing Gestures” in the iPhone Development Guide of the iPhone Reference Library.
The simulator can’t do the following: n
No camera means you cannot simulate any of the image-capture functionality of the iPhone.
n n n
Although there are options to rotate the simulator, you cannot fully simulate the accelerometer.
Core Location and Map Kit will always report your location as Apple’s headquarters in Cupertino.
You cannot simulate more than two touches at once.
n n n
The simulator has no iPod, iTunes,
Calendar, Mail, SMS, Phone, or Maps applications.
The Settings application has only limited functionality; for example, it doesn’t have airplane mode or data settings.
It doesn’t have a proximity sensor.
A
The simulator showing a call in progress.
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B
Drag an image onto the simulator to have it open in Safari.
If your application needs access to any of these functions, you will need to test your code on an actual iPhone rather than on the simulator.
Since there is no camera on the simulator, to add photos to the Photos application, you must follow these steps.
To add photos:
1. Open the simulator, and make sure you are at the iPhone desktop screen.
2. Drag any image from your computer’s desktop onto the iPhone Simulator.
Safari will open on the simulator with your photo displayed
B
.
3. Touch and hold the photo. A dialog box will pop up allowing you to save the image to the Photos application.
Once your applications are installed on the simulator, you can touch and hold to change their order or delete them—just as you can on a real iPhone.
Choosing Reset Content and Settings in the iPhone Simulator menu will remove all applications and reset the simulator to its initial configuration. However, it also deletes the default address book and photo album data.
You can back up this data before you reset the simulator by copying the contents of ~/Library/
Application Support/iPhone Simulator/User.
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About Interface
Builder
Interface Builder (often abbreviated IB) is a visual tool used for creating your iPhone user interfaces.
IB lets you visually lay out the interface just as it would look on the iPhone, adding elements such as buttons, views, and labels and setting properties such as color and size.
You can also visually connect your interface to your application’s code using a special system that encompasses outlets and actions.
An outlet is a connection from your code to your user interface. Imagine you have a label in your iPhone application that you want to display a message with. Using IB, you drag this label onto your interface.
You then create an outlet between your code and your interface, which allows you to manipulate the properties of the label programmatically in your code.
An action goes the other way: from your interface to your application code. If you had a button on your interface that you wanted to have call a certain piece of code when clicked, you would create an action in your code and then hook up the button to this action in IB. When the button is clicked, the code is executed.
These concepts are common among many languages with visual design tools; however, the process of creating outlets and actions can be somewhat confusing at first.
You’ll examine this later in the chapter.
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A
The contents of the XIB file.
Your interface is saved as an XML-format
XIB file. When you build your application, the XIB files are compiled into a deployable NIB file, which is then packaged up with your application bundle. At run time, your iPhone application will automatically unpackage and load these files to re- create your user interface.
Now you’ll take a quick look at the various elements of the IB interface.
In Xcode, double-click the file named helloWorldViewController.xib (in the XIB
Files group of the Groups & Files pane) to open your XIB in IB.
There are three main parts to the IB interface: the document window, the Library window, and the inspector window.
NIB stands for “NeXT Interface Builder.”
The file format was originally created for the NeXT operating system in the 1980s.
The newer XIB format was introduced in
Xcode 3.0. In this chapter, XIB and NIB both mean an Interface Builder file.
About the document window
The document window shows the contents of the XIB file
A
. In this example, you can see three objects.
n
File’s Owner—This is a proxy object representing an instance of a class (in this case the
helloWorldViewController
class). You will create your outlets and actions in objects like these.
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n n
First Responder—Every XIB will have a First Responder object, providing an entry point for your interface into the responder chain, which consists of a list of objects connected together.
Touch and motion events are sent to the first object in the chain (the
firstResponder
), which can choose to process it or pass it on up the chain to the next object via its
nextResponder
property.
All UI objects (including
UIView
s and
UIWindow
s) are responder objects, as is your
UIApplication
. You can create custom actions on this object and have your visual elements call these actions.
Objects in the responder chain can then handle these custom actions.
View—This represents the interface of your iPhone application (in this example it is an instance of a
UIView
class).
Note: Here you have only a single object placeholder and a single view.
It is, however, quite possible (and common) to have more than one of each within a single XIB file.
Often an interface can have many nested UI controls on it: labels on buttons within views within yet more views. This can make it very difficult to determine which object is which in the document window. Although you can name your objects (by clicking the label underneath them), the View Mode options at the top left make it much easier to visualize these hierarchies
B
.
B
Changing the view mode of the XIB to visualize the object hierarchy.
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C
The Library window.
D
The inspector window.
Mode selector
Organization drop-down
Item pane
Details pane
Filter area
About the library window
The Library window is divided into three main areas
C
.
n
Organization drop-down—Divides your objects into functional groups n n
Item pane—Lists the contents of the currently selected group (or groups), graphically depicting the functionality the object performs
Details pane—Shows the name and a brief description of what the selected object is and what it does
You can filter the items shown by entering search text in the filter control at the bottom of the Library window.
Notice the mode selector tabs at the top, which allow you to switch between user interface objects, classes, and media resources. Resources will include the images and sound files within your project.
Just as with the Groups & Files pane of
Xcode, you can create your own groups and smart groups in the Organization pane of the
Library window.
The Action menu at the bottom of the
Library window allows you to modify the way items are presented.
About the inspector window
The inspector window allows you to configure the properties and settings for each of the elements within the document window
D
. It’s divided into four panes.
n
Attributes—This is the main area for setting the visual properties of your UI elements, such as colors, fonts, and text.
You can also set drawing properties and choose whether an element can respond to touches from the iPhone screen.
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n n
As you click each object in your document window, notice how the inspector window automatically updates to show the different properties and settings available for each object.
Connections—This pane displays the outlets and actions for the currently selected object. If an outlet or action is connected, you will see the name of the object it is connected to
E
. You’ll take a look at how to go about connecting outlets and actions later in this chapter.
You can also see the connections for an object by Control+clicking it in the document window
F
.
Size—This pane allows you to set the origin (the x and y coordinates) and size (width and height) of your visual elements. You can also adjust the autosizing behavior of your elements, which can be useful when your interface changes from portrait to landscape mode. Autosizing is intuitively shown by a small animation next to the control
G
.
E
Outlets are visually represented in the Connections pane.
F
Control+click to view an object’s outlets and connections.
G
The Size pane of the inspector window.
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H
The Identity pane of the inspector window.
I
Changing a class in the
Identity pane.
n
Identity—The Identity pane shows you the class of your object, allowing you to override this with your own custom class should you choose to do so. You can visually add outlets and actions here and set the name used to display your objects in the document window
H
.
The Identity pane is also the key to adding nonvisual instances of your own classes to your XIB files. After creating and saving your class in Xcode, simply drag an NSObject from the Library window and then rename its class to your own class name
I
.
You’ll now take a look at how to use all of this to create your own interface.
To create the interface:
1. Drag a UIButton from the Library window, drop it on your view, and set its text to Click Me.
2. Drag a UILabel from the Library window, and drop it on your view above the button
J
.
3. Save your interface, go back to Xcode, and build and run your application.
You can click the button, but at the moment nothing happens.
J
Visually lay out your application by dragging elements onto the iPhone canvas.
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Now you will update your application to have it display the current time when you click the button.
To update the application:
1. Back in IB, update the UIButton text to Show Current Time. You do this via the inspector window or just by doubleclicking the button and typing. Notice how the button automatically resizes itself to fit the wider text. Resize your label to make it the same width as your button, and set the text alignment to center (the Alignment property is on the
Attributes pane of the inspector window).
2. Select the Classes mode selector in the Library window, and select the helloWorldViewController object.
3. Select Actions from the drop-down. In the Class Actions area, click Add (+), and set the action to buttonClick
K
.
4. Select Outlets from the drop-down, and add an Outlet called labelTime. Change the type to UILabel
L
.
5. Making sure your File’s Owner object is still selected in the document window, click the Connections pane of the inspector window.
K
The Library window showing your class’s actions.
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The Library window showing your class’s outlets.
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M
Hooking up the interface by dragging between elements.
N
Connect actions by dragging between the actions window and the object you want to receive the action.
6. Connect the outlet by clicking the small circle on the right side of the labelTime outlet. Keep your mouse button pressed, and drag to the label on your view to make the connection
M
.
7. To connect the action, you need to do the reverse. Click your button in the document window, select the Touch
Up Inside event, and drag to your File’s
Owner object. Select the buttonClick: action when it pops up to make the connection
N
.
8. Choose File > Write Class Files from the main menu. Then click Save
O
.
9. Click Replace in the next dialog box (or, if you like, you can click Merge to see what is happening).
10. Back in Xcode, open the file named helloWorldViewController.h. Notice how
IB has generated code for the outlet and the action:
@interface
helloWorldViewController :
UIViewController {
IBOutlet UILabel *labelTime;
}
- (IBAction)buttonClick:
(id)sender;
@end
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O
Updating your code with the outlets and actions you’ve just created.
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11. In helloWorldViewController.m, edit this stub code so that it looks like this:
- (IBAction)buttonClick:
(id)sender {
NSDateFormatter *dateFormatter
= [[NSDateFormatter alloc]
init];
[dateFormatter setDateFormat:
@”hh:mm:ss”]; labelTime.text = [dateFormatter
stringFromDate:[NSDate date]];
[dateFormatter release];
}
12. Build and run your application. You should now be able to click the button, and the label will update to show the current time
P
.
In the previous example, you got IB to automatically generate the stub code for your outlet and action. Although this is convenient, you wouldn’t normally do it with anything other than an empty class.
It’s much more common to create your outlets and actions yourself in Xcode manually and then use IB to hook them up to your user interface. Now you’ll take a look at how you do this.
To manually create outlets and actions:
1. In Xcode, open the file named helloWorldViewController.h, and edit it to look like Code Listing 2.1. You will have created two more outlets and replaced your
buttonClick:
action with one called
controlChanged:
.
P
The application running in the simulator.
Code Listing 2.1 The header file for the hello world application.
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2. Switch over to helloWorldViewController.m, and edit it to look like
Code Listing 2.2.
You have modified your code, moving the label update into its own method and adding the option to display the date or the time. You’ve also added the ability to modify the font size of the label. Notice also that you call this method in the
viewDidLoad
method.
This is so the label shows correctly when the application first starts.
3. In the Groups & Files pane, doubleclick your helloWorldViewController.xib file to open IB. Delete the button from your interface, and drag two labels— a UISwitch and a UISlider—onto your view. Arrange them so they look like
Q
. Notice how you’ve also increased the width of your time label to handle a larger font. continues on next page
Q
Adding some more elements to the interface.
Code Listing 2.2 The updated code for the hello world application.
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4. Select your UISlider, and edit its
Minimum Value setting to 10 and its Maximum Value setting to 25
R
.
5. Keeping your UISlider selected, press the Control key, and drag from the slider to the File’s Owner object in the document window
S
. Then select controlChanged: in the pop-up menu.
This is a shortcut method of connecting outlets and actions: Instead of using the Connections menu, you can simply
Control+drag between objects to have the default action connected. Also connect the outlet from the File’s Owner to the UISlider.
R
Configuring the slider.
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Connecting the slider to the controller.
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T
The updated application.
6. Repeat step 5, but this time for the
UISwitch control, again selecting the controlChanged: option. Notice how you can have multiple controls connected to the same action. Again, also connect the outlet from the File’s
Owner object to the UISwitch control.
Back in Xcode, build and run your application. You should be able to switch between the date and time, as well as change the font size by moving the slider
T
.
Although IB automatically scans your code for
IBAction
and
IBOutlet
definitions in your header files, it can occasionally miss them, and you’ll find you can’t see your outlets and actions in the inspector window. You can solve this by manually dragging the .h file of your class from the Xcode Groups & Files pane onto the IB documents window.
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Why are there two XIB files in the project?
In the previous example, you may have noticed that you are working only with helloWorldView
Controller.xib, but your project actually contains two XIB files. So, what does MainWindow.xib do?
In the Xcode section, the <app>-Info.plist file has the property Main Nib File, which is the NIB that is loaded automatically when your iPhone application starts. MainWindow.xib is this file.
Opening MainWindow.xib, you can see several objects:
.
File’s Owner—
An instance of UIApplication representing the entry point of your application, created by the UIApplicationMain() function call in main.m. You will only ever have a single
UIApplication
object in your iPhone applications.
.
.
helloWorld App Delegate—
An instance of your helloWorldAppDelegate class
(the helloWorldAppDelegate.h and helloWorldAppDelegate.m files in your project). Since this object is the delegate of your UIApplication, it handles all of the startup behavior of your application.
Notice it has viewController and window outlets.
helloWorld View Controller—
An instance of your helloWorldViewController class (the helloWorldViewController.h and helloWorldViewController.m files within your project).
If you inspect this object in the inspector window, you will notice that it has its NIB Name property set to helloWorldViewController
U
.
This tells the object to initialize itself from the helloWorldViewController.xib file. This is how the XIB file you have been working with so far gets loaded.
U
The NIB Name property.
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Why are there two XIB files in the project?
(continued)
When an XIB is loaded, every object inside is created. By using this pattern of one XIB per view controller, you can lazily load your interface as you need it. This decreases your application’s loading time and uses less memory. Having your views and view controller in individual XIB files also makes things easier to work with in IB—imagine how complex the outlets and actions would be if everything were in a single file!
.
Window—
Represents the top-level or root view in your application’s interface. You will only ever have a single window in your application; views you create will be added as subviews to this object. Having this top-level view ensures that things like alert dialog boxes will always appear above your own views.
When your application is launched, the interface is created
V
.
V
An overview of how the application is constructed.
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About the
Documentation
As you saw earlier when looking at Xcode, iOS includes a comprehensive and powerful documentation viewer. You can launch the documentation viewer by using the Help menu, by pressing Option+Command+?, or by selecting a symbol in your code and
Option+double-clicking.
Documentation is presented in an HTMLbased, multiframe layout that allows you to move around related information by clicking hyperlinks in the text, just as you would in a Web browser
A
.
Above the main documentation pane, a history of your path through the pages is maintained, allowing you to navigate forward and backward or jump directly to a page via the pop-up menu.
In the left pane, you can subscribe to documentation feeds from Apple, which automatically update when new documentation becomes available. You can bookmark the page you are currently viewing by clicking the Bookmark button in the toolbar
B
.
You can search the documentation by API
(the fastest) or by document title; you can even search the full text of the documentation. The filter pane at the top allows you to limit searches to only the documentation sets and technologies in which you are interested.
Pressing the Command key while clicking links in the documentation will make the page open in a new window.
The latest documentation is also available online at http://developer.apple.com/iphone.
A
The documentation browser.
Bookmark toolbar button
B
The Bookmarks pane.
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The Xcode Organizer
The Xcode Organizer provides convenient access to a number of tasks you will need to perform during the iPhone development process. You can open the Organizer by selecting it from the
Window menu in Xcode or by pressing Control+Command+O. The interface consists of two panes with a number of items on the left and their corresponding details on the right. Within the Organizer, there are several sections to explore.
Unique device identifier
The unique device identifier (also known as a UDID) is a way of identifying an iPhone or iPod.
This identifier is used when adding devices in the iPhone Provisioning Portal and is also used when generating both Development and Ad Hoc provisioning profiles. A provisioning profile is necessary to run your application outside of the iPhone Simulator on an actual device (iPhone, iPod, or iPad). You would generally create three provisioning profiles: a Development profile associated to your own iPhone’s UDID; an Ad Hoc profile used for beta testing, associated with up to
100 other UDIDs; and a Distribution profile used when submitting your application to the App Store on the iTunes Connect Web site. You can find details on creating and managing code-signing identities on the iPhone provisioning portal at http://developer.apple.com/iphone.
Clicking the Save As Default Image button on the Screenshots tab allows you to add a graphic to your project to be used as a load screen when your application first starts
A
. It is common for developers to use the opening or initial screen of their application as a load screen. This gives the impression of a speedy load time, even if the application has not yet fully loaded.
A
The Screenshots tab allows you to manage and capture screenshots from a connected device.
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Projects & Sources
This area gives you access to frequently used directories and files. You can drag any item into this area, as well as perform other frequent operations such as editing, moving, and deleting files and directories
B
.
You can even build and run projects directly from this area rather than opening them in Xcode.
Devices
The Devices section lists any iPod, iPhone, or iPad that can be used for development purposes. If a device is currently attached to your computer, an indicator graphic appears, showing whether it can be used for development (green) or whether there is something wrong (yellow or red). For example, you must have the correct SDK installed on your computer for the operating system currently running on the device
C
.
Selecting a device displays information including the device capacity, serial number, identifier, and which version of iOS your device is running
D
. If the device is connected, you will also be shown a list of all the provisioning profiles and applications installed on it. You can manually install and remove provisioning profiles by dragging them into the list or by using Add (+) and
Delete (–). Similarly, you can add any applications you develop yourself to your device in this way rather than using iTunes.
The tabs at the top allow you to see logging information for your application both on the device and on your computer. You can also capture screenshots of any application running on your iPhone from here, which can be very handy when submitting to the iTunes Connect Web site. You can also drag images in this area onto your computer desktop.
B
Editing a file directly in the Xcode Organizer.
D
The device summary page.
C
A graphic indicates the status of any connected devices.
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E
The Sharing section helps with validating an deploying an iPhone application.
F
Deployment options for sharing an application.
iPhone Development
This area allows you to manage a number of tasks specific to iPhone development: n
Archived Applications—This lists all the archives created as a result of using the Build and Archive command from within Xcode. This command will create an archive containing your application bundle (.app) and the debug symbols file (.dSYM) used to decode any crash logs generated by an Ad Hoc or release build of your application. Archives are stored in the ~/Library/MobileDevice/
Archived Application directory. Using the buttons underneath
E
, you have three options for working with archived applications.
n n
Validate Application—This runs a number of validation tests on your application, such as checking for the correct icon, checking that your .plist is correctly configured, and checking that the application has been correctly codesigned. You should always validate your application before submitting to the iTunes Connect Web site.
Share Application—This provides a convenient way of creating Ad Hoc distributions of your application, often used when beta testing an application. You can choose to save to disk or e-mail the application directly from this screen
F
.
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n n n n n n
Submit to iTunesConnect—This allows you to sign your application with your
Distribution identity and upload it directly to Apple for submission to the
App Store. Note that you can submit only the application binary using this function. You need to have already set up the application on the iTunes Connect Web site, along with associated screenshots, description, keywords, and so on.
Developer Profile—This shows details of all the certificate identities and provisioning profiles installed on your computer. These are necessary for you to be able to install and run your applications on an iPhone, iPod, or iPad. The
Import and Export profile buttons at the bottom of this screen provide a convenient way of migrating your identities and profiles between computers
G
.
Device Logs—This displays all the log files on any device paired with your computer. This can be handy for trying to figure out the cause of a crash in your applications. You can also see logs generated by the other applications on your iPhone.
Provisioning Profiles—This lists all the provisioning profiles available and which of your devices they are installed on.
Screenshots—This shows all the screenshots you have taken from any devices previously attached to your computer.
Software Images—This lists any operating software images you have on your computer
H
. Right-clicking an image lets you reveal the location of the image in the Finder, which can be handy should you need to restore a device to a different version of an operating system.
G
The Developer Profile section shows you the identities and profiles installed on your computer.
H
Showing the versions of the iPhone OS available on your computer.
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Common Tasks
This chapter will show you some of the useful tips and tricks that are essential for building a great iPhone application. You’ll start by looking at the application startup process, where to put your code, and how you set the various configuration options.
Next you’ll see how easy it is to add user and application preferences to your applications. You’ll also learn how to create an application preference page within the
Settings application.
Then you’ll learn about some of the techniques you can use to internationalize an iPhone application, making it available in different languages. You’ll also find out how to make your applications accessible to people with visual impairments.
Finally, you’ll learn how to launch other applications from your own, as well as some techniques for sharing data between applications.
In This Chapter
Application Startup and Configuration
Localization
Accessibility
Interapp Communication
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94
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Application Startup and Configuration
In this section, you’ll learn what happens when you tap the icon to launch your iPhone application. You’ll see how you can respond to different stages in the application startup and shutdown processes. You’ll also look at some of the configuration options available for your applications and how to work with user and application preferences.
Using the application delegate
The application delegate, represented by the
UIApplicationDelegate
class, is the starting point for all iPhone applications.
Since there is only a single application delegate, it can be a useful place to put methods and variables you want to be available globally.
You add a reference to the application delegate from within your classes by writing this:
id appDelegate = [[UIApplication
sharedApplication] delegate];
(You also need to remember to import the header file of your application delegate.)
However, since the application delegate needs to be loaded before your application can begin, it’s probably good practice to avoid putting code there unless absolutely necessary. Instead, you can adopt a “lazy loading” style of programming where you create objects only when needed. This has the added benefit of keeping the memory footprint of your applications to a minimum.
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The application delegate serves as both the first place (when your application loads) and the last place (before your application exits) that you can execute some code. It provides a number of important methods: n
applicationDidFinishLaunching:
—
This is the first method called when your application has loaded. This is a good place for you to perform application- wide initialization of data such as loading any previous state or settings.
n n
applicationDidFinishLaunching
WithOptions:
—If implemented,
applicationDidFinishLaunching:
will be ignored, and this method will be used instead. The
launchOptions
parameter is a dictionary containing information used in two scenarios:
It will be used if your application was launched as the result of a “push” notification, in which case
launchOptions
will contain a dictionary of information relating to the notification. See the
Apple Push Notification Service Programming Guide for more information on working with push notifications.
It will be used if your application was launched as a receiver of a URL resource. See the “Interapp Communication” section later in this chapter for more information.
applicationWillTerminate:
—This is the last chance to perform any action before your application exits. This is a good place for you to free memory and save application state or settings such as user preferences.
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n n n
applicationDidReceiveMemory
Warning:
—This is called whenever the device is running low on memory due to improper memory management or simply because your application is trying to load too much data into memory. Normally you would attempt to free as much memory as possible in this situation by releasing any cached or unnecessary objects.
If this method is called, then the corresponding
didReceiveMemoryWarning
delegate method will also be called on every view controller class in your application. This gives you granular control over your application, allowing you to clean up memory on a per-view controller basis. Although optional, it’s recommended that you try to implement this method, because your application may become unstable or crash if memory warnings are ignored.
applicationWillResignActive:
—
This is called just before your application becomes inactive. This can happen if another window pops up over your application (for example, an incoming phone call) or if the device goes into a locked state, either by going to sleep or by the user pressing the power button.
applicationDidBecomeActive:
—
This is the reverse of the previous method and will be called every time your application becomes active. This obviously happens when the application is first launched but also when you dismiss any windows that have appeared over your application (for example, an incoming text message) or when the device wakes from a locked state. You can prevent your application from going to sleep by writing this:
[[UIApplication sharedApplication]
setIdleTimerDisabled:YES];
Some applications have splash screens that display while the application is loading.
You can add a splash screen to your own application by adding a file called Default.png to the project. Rather than displaying a graphical splash screen (which can itself increase load time), many developers opt to show an image that replicates the initial screen of the application.
After your application has launched, you can use the UIDevice class to determine information such as the make, model, operating system name, and version of the device on which it’s running.
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A
The Info.plist file contains the configuration settings for your application.
Understanding application settings
As mentioned in the “About the Xcode IDE” section in Chapter 2, “The iPhone Developer’s Toollbox,” the <app>-Info.plist file contains many of the preferences and settings used when launching your application
A
. Table 3.1 summarizes some of the more commonly used settings.
Working with user preferences
User preferences are generally stored using the
NSUserDefaults
class, also known as the defaults system. You would normally read from the defaults system when your application first launches to restore any previous settings for the user or application.
The
NSUserDefaults
object is quite smart.
When your application launches for the first time, there obviously won’t be any user preferences (other than those you set programmatically). Once you set a value, the defaults system will automatically save it for you. The next time you launch the application and request the value, it will be returned to you. All the complexities of dealing with loading and saving files and values are hidden, and for performance everything is cached in memory.
This cache is periodically refreshed automatically.
To begin using the defaults system, you first get a reference by writing this:
NSUserDefaults *prefs =
[NSUserDefaults
standardUserDefaults];
You can then read values by using something like this:
NSInteger age =
[prefs integerForKey: @"age"];
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TABle 3.1 Commonly Used < app > -Info.plist Settings
Key
Application does not run in background
Application supports iTunes file sharing
Application requires iPhone environment
Application uses Wi-Fi
Description
If you want your application to terminate rather than move into the background when quit, set this property to True. For information about multitasking, see
Chapter 11.
This property allows you to share files in your application’s documents directory with your desktop computer via iTunes.
If your application does not run on an iPod touch, set this to True.
Bundle display name
Bundle identifier
Bundle version
If your application requires Wi-Fi to function, you should set this property to
True. Doing so will prompt the user to enable Wi-Fi if it is not already enabled.
For power-saving, the iPhone automatically closes any Wi-Fi connections in your application after 30 minutes. Setting this property will prevent this from happening and keep the connection active.
This sets the name of your application, displayed below the icon on the iPhone screen. You are limited to approximately 10 to 12 characters for an application name before the iPhone abbreviates the name.
This sets the unique identifier for your application setup in the iPhone
Developer Program Portal Web site.
This sets the version number of your application. This is the used in the iTunes
App Store and should be incremented each time you deploy a new version of your application.
Icon already includes gloss and bevel effects
Icon file This is the filename of your application’s icon (added to your project).
Initial interface orientation This determines whether your application starts in landscape or portrait mode.
Launch image
By default, the iPhone applies a “gloss effect” to application icons. Setting this key to True will prevent this.
Localizations
This property allows you to specify the name of the launch image file for your application. This can be handy when building universal applications as you can specify a different launch image for iPad, iPhone, and iPod touch devices.
This is a comma-delimited list of localizations that your application supports.
For example, if your application supports English and Japanese, you would use
English,Japanese. You should then provide the appropriate localization strings for each language. See the “Localization” section later in this chapter for more details on how to localize an application.
Status bar is initially hidden
This allows you to launch your application without a status bar. Your application interface will automatically resize to fill the entire iPhone screen.
Required background modes
If your application supports multitasking and runs in the background, this key lets you specify which services it should be allowed to run. For more infiormation multitasking, see Chapter 11.
Status bar style
Supported interface orientations
If you leave the status bar visible, this key allows you to select from one of three different display styles.
This key allows you to specify the initial orientation of your application when it first launches.
Main nib file base name This is the XIB file loaded when your application first starts. You would not normally need to modify this value.
URL types This is an array of URL identifiers supported by your application. See the “Interapp
Communication” section later in this chapter for details on how to use this value.
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You write values by using this:
NSInteger age = 30;
[prefs setInteger:age forKey:@"age"];
Code Listing 3.1 shows some examples of reading and writing to the defaults system.
The defaults system has methods for working with property list datatypes (
NSNumber
,
NSString
,
NSData
,
NSArray
, or
NSDictionary
). If you want to store more complex values, you need to archive the value and store it as an
NSData
instance.
You can then unarchive when reading the value back to convert from an
NSData
instance to the original datatype.
Code Listing 3.1 Some examples of reading and writing to the defaults system.
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For example, to archive and store a
UIColor
object in the defaults system, you would use this:
UIColor myColor =
[UIColor blueColor];
NSData *colorData = [NSKeyedArchiver
archivedDataWithRootObject:
myColor];
[prefs setObject:colorData forKey:
@"myColor"];
To then unarchive and restore the value, you write this:
NSData *colorData = [prefs
objectForKey: @"myColor"];
UIColor myColor = [NSKeyedUnarchiver
unarchiveObjectWithData:colorData];
While developing your applications, it is possible to force-quit them (by pressing
Command+Q). Although this is not something that can happen when your application is in production, doing so may mean that the defaults system does not save correctly. You can get around this problem by calling the synchronize
method, which will force the defaults system to be saved and written to disk.
Application preferences
Just like user preferences, application preferences are stored and retrieved by using the
NSUserDefaults
class and are managed in the same way in your code.
iOS provides a second mechanism for managing application preferences, allowing you to create a page in the global
Settings application
B
. The user can then edit the application preferences by using this page.
B
The Settings application can be used to edit your application settings.
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C
Adding a settings bundle to your project.
To create a settings page for your application:
1. In Xcode, select File > New File.
2. Select the Resource section, and select
Settings Bundle to create a new settings bundle
C
.
3. Save the file as Settings.bundle.
4. Build and run your application.
5. Switch to the Settings application. You will notice a new section with the same name as your application. Select this section to open the settings page showing four elements
D
.
6. In Xcode, expand the Settings.bundle file in the Groups & Files pane, and select the Root.plist file.
7. In the editing window on the right, expand the PreferenceSpecifiers section
E
.
The four items (items 1–4) represent the four interface elements in the settings page from step 2. If you expand each element, you will notice they all have a
Type key, which determines the control type to display.
D
The settings page of your application.
E
The PreferenceSpecifiers key contains the various items in the settings page.
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Adding controls
You can add seven types of controls to your settings page: n n n n
PSGroupSpecifier
creates a new group of controls, such as a settings page with several groups
F
.
PSTextFieldSpecifier
creates a text field where the user can enter a string of text
G
. This control has several properties:
isSecure
stops the text you are entering from being shown as it’s typed. This is useful for passwords and other sensitive information.
DefaultValue
lets you specify a default value if no value has been set.
KeyboardType
allows you to specify which keyboard is shown when the user taps the control.
AutoCapitalizationType
controls the type of capitalization that occurs as the user types.
PSToggleSwitchSpecifier
creates a toggle (on/off) switch. The
DefaultValue
property determines whether the switch is on or off by default.
PSSliderSpecifier
creates a slider.
You use the
MinimumValue
and
MaximumValue
properties to determine the range of the slider, and you use the
DefaultValue
property to determine the starting value.
F
A settings page with three groups.
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Entering text into a settings page.
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H
Use the
PSMultiValueSpecifier
type to select from a set of multiple values.
I
Choosing from a set of values.
n n
PSTitleValueSpecifier
creates a simple read-only label. Use the
DefaultValue
property to set the text of the label.
PSMultiValueSpecifier
creates a second view consisting of a table of values that the user can select from
H
.
The
Values
property contains an array of possible values. The corresponding
Titles
property contains the display labels for each value and accepts an array of values to display
I
. The
DefaultValue
property determines which value is initially selected.
n
PSChildPaneSpecifier
allows you to create another settings view. By setting the
File
property to the name of another setting’s plist, you can nest settings within settings.
For all the control types (except the slider that has no title), the
Title
property enables you to set the title text that appears to the left of the control.
The
Name
property of each control is the key you use to reference the setting with
NSUserDefaults
. For example, to get the value of the
PSToggleSwitchSpecifier
toggle switch defined in item 3 of the
PreferenceSpecifiers
array, you would write this:
NSUserDefaults *prefs =
[NSUserDefaults
standardUserDefaults];
BOOL enabled = [prefs boolForKey:
@"enabled_preference"];
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localization
Localization refers to the representation of currency, dates, times, and numbers for a regional variant of a language called a locale . For example, currency and dates are displayed differently for the United
Kingdom than they are for the United
States. Internationalization, on the other hand, refers to representing the text (and possibly other user interface elements) of your application in the end user’s language. In this section, the term localization is used to mean both of these concepts.
You can localize numbers and dates by using the localization support of the
NSNumberFormatter
and
NSDateFormatter
classes. For example, to display a localized currency value, you can use this:
NSNumber *currencyValue = [NSNumber
numberWithFloat:1000.23];
NSNumberFormatter *formatter =
[[NSNumberFormatter alloc] init];
[formatter setNumberStyle:
NSNumberFormatterCurrencyStyle];
NSLog(@"Formatted value for locale
%@ is: %@",
[[formatter locale]
localeIdentifier],
[formatter stringFromNumber:
currencyValue]);
The user’s locale is automatically detected based on their phone settings.
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A
B
Creating the en.lproj and fr.lproj directories in your project directory.
C
A French strings file.
Adding a strings file to your application.
Words and phrases, however, are unique to each language and must be treated differently. You must create a strings file for each language that you want your application to support
A
. Strings files consist of a list of key-value pairs, where the “key” is the source representation of the word or phrase (which will be in the language used by the developer) and the “value” is the localized version of the word or phrase.
To create a localized application:
1. Create a new view-based application, saving it as LocalizationExample.
2. Open the directory where you have just saved your project in Finder.
3. Create two directories: one representing English called en.lproj and one for
French called fr.lproj
B
.
These directories are where you will be storing the localized resources for your project.
4. In Xcode, select File > New File.
5. In the Mac OS X section on the left of the New File dialog box, select the
Other section, and choose Strings File from the file types
C
.
6. Click Next, and save the file as
Localizable.strings in the en.lproj directory created in step 3.
7. Repeat step 6, creating a second
Localizable.strings file, but this time saving it in the fr.lproj directory.
You should now see a new item in the
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8. Expand this item, and you will see that
Xcode has intelligently grouped both of your strings files together
D
.
9. Select the English strings file (“en”), and enter the following:
"HelloKey" = "Hello World!";
This is a key-value pair, and the key
(
HelloKey
) has a value of
"Hello
World!"
. Notice you end the entry with a semicolon.
10. Repeat step 9, but this time add the entry to the French strings file (“fr”):
"HelloKey" = "Bonjour Monde!";
Again, you use the same key, only this time you have specified a different, localized value.
11. Switch to LocalizationExample.m, uncomment the
viewDidLoad
method, and write the following code:
CGRect lblFrame = CGRectMake
(110,10,200,40);
UILabel *lblLocalized = [[UILabel
alloc] initWithFrame:lblFrame]; lblLocalized.backgroundColor =
[UIColor clearColor]; lblLocalized.text = NSLocalized
String(@"HelloKey",nil);
[self.view addSubview:
lblLocalized];
Here you are just creating a label and adding it to your main view. Notice, however, that you set the text using the
NSLocalizedString
function. You pass this function a key for the localized text you want to display, and the function retrieves the localized text for you from the strings file.
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E
Selecting a different language.
12. Build and run your application.
You should see “Hello World!”
13. To see the French localization, switch to the Settings application, select
General > International > Language, and choose French
E
. Switch back to your application, and you should see the text now in French.
You can localize your application’s settings and user interface in the same way by copying the <app>-Info.plist and
XIB files to the localized en.lproj and fr.lproj directories.
Notice that the second parameter of the
NSLocalizedString
function was not used.
It’s there to allow you to provide a comment for each of your localized strings. You can then use the genstrings tool to parse your source code and automatically generate strings files for you. For information on how to use the genstrings tool, see the “Strings Files” section of the Apple Internationalization Programming
Topics documentation.
In the example here, you created localized strings using the language codes for
English (“en”) and French (“fr”) to name the directories. For a complete list of available language codes, refer to the Unicode Consortium homepage at http://www.unicode.org.
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Accessibility
In the context of an iPhone application, accessibility means providing audible cues to describe the meaning and function of the user interface in your application.
VoiceOver is an Apple technology that allows a user to interact with an iPhone without having to actually see the screen.
The iPhone can speak to describe elements of the user interface, which buttons and controls are available, and which actions a user can take.
You can easily add VoiceOver support to your own applications by using the
Accessibility API. All the standard UIKit controls and views are already accessible by default—you just need to provide the descriptive text for VoiceOver to speak.
To test your applications for Accessibility, you will need to enable VoiceOver support in iTunes.
To enable VoiceOver for your iPhone:
1. Launch iTunes, making sure your iPhone is attached to your computer.
2. Select your iPhone in the Devices section of the source list. Scroll to the bottom of the Summary tab, and click
Configure Universal Access in the
Options section
A
.
3. Make sure that VoiceOver is selected in the Universal Access pop-up window, and click OK
B
.
A
Accessibility is enabled via iTunes.
B
Enabling VoiceOver.
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C
D
iPhone accessibility settings.
Creating the user interface for your accessible application.
E
Select Device to install the application on your iPhone.
4. Press the Sync button to update your iPhone.
You can test that VoiceOver is working by selecting any interface element to hear a description. Note that your iPhone’s controls function a little differently than normal when in VoiceOver mode. You must double-tap to select an item and use three fingers simultaneously to scroll. You can configure more of the Accessibility features on the iPhone by selecting Settings > General >
Accessibility
C
.
Making your applications accessible
Now that you’ve enabled VoiceOver on your iPhone, you’ll create a simple application with accessibility features enabled.
To create an accessible application:
1. Create a new view-based application, saving it as AccessibleExample.
2. Expand the Resources group, and doubleclick AccessibleExampleViewController.xib to open Interface Builder.
3. Drag a
Label
,
Text Field
, and
Button
onto your view.
4. Select the label, and change its text to Name.
5. Select the button, and change its title to Save
D
.
6. Save your interface, and go back to
Xcode.
Since the iPhone Simulator does not support VoiceOver, you will need to select Device as the active SDK in
Xcode
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7. With your iPhone connected to your computer, build and run the application to install it onto your iPhone.
You should be able to tap the label, text field, and button of the application to hear audio descriptions of them.
In this example, tapping the label made the iPhone speak its value, while the text field simply spoke the words “Text field, double-tap to edit.” Ideally, you would also want VoiceOver to describe the meaning of the text field. Similarly, when tapping the
Save button, VoiceOver says, “Save, button.” Again, although descriptive, this may not be as much information as you want to convey to the user.
Next you’ll improve the values that
VoiceOver uses when describing the functionality of your interface.
To improve the descriptions
VoiceOver uses in your applications:
1. In Interface Builder, select the text field, and make sure the Attributes inspector is showing.
You can show the Attributes inspector by pressing Command+1 or selecting it from the Tools menu.
2. Select the Identity tab of the Attributes inspector, and expand the Accessibility section.
3. In the Label text box, type “Enter your name here” as the value, and click the
Save button on your interface
F
.
4. On the Identity tab of the Attributes inspector, set the Hint text box to “Tap this button to save”
G
.
F
Setting the Label accessibility attribute of the text field.
G
Setting the Hint accessibility attribute of the Save button.
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H
The accessibility traits of the
Save button in the previous example.
5. Save your interface, and go back to
Xcode. Build and run your application, again ensuring that iPhone Device is selected as the active SDK. Tap the text field and the Save button again to hear more meaningful descriptions spoken by VoiceOver.
Accessibility attributes
You’ve seen how simple it is to add basic
VoiceOver support to your application and how to add more meaningful descriptions to the audio cues spoken. The Accessibility API defines five attributes to use when adding accessibility features to your applications: n n
Label—A short, simple word to describe the control, for example Name or Save.
Hint—A longer, more descriptive phrase to describe the meaning or action of a control, for example, “Tap to save.” n n n
Traits—A combination of one or more elements to describe the behavior of a control
H
.
Value—The value of the element or control. The label in the previous example had a value of Name. Generally, the Accessibility API will use this if the element’s value can be changed or can’t be easily described by the label.
Frame—The frame of the element onscreen. This is used by the accessibility API to report the control’s location onscreen.
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You can read more information on adding accessibility support to your applications, including how to do so programmatically
(rather than using Interface Builder as you have in these examples), by referring to the Accessibility Programming Guide for iPhone OS in the developer documentation.
In the previous examples, you had to install the application on your iPhone to test it. Although Interface Builder doesn’t support VoiceOver, it does offer a tool called the
Accessibility inspector to help when developing accessible applications. The Accessibility inspector appears as a floating window in your application’s interface. Selecting any item on the interface shows its accessibility properties
I
. You can enable the Accessibility Inspector in the simulator by selecting Settings > General > Accessibility
J
.
I
The Accessibility inspector can be used to test your application from the iPhone Simulator.
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Enabling the Accessibility inspector in the iPhone Simulator.
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A
Launching the Mail application.
Interapp
Communication
Although the iPhone doesn’t allow more than one application to run at a time, you can launch another application from your own, and you can share data between applications.
You can launch one application from another by using the
openURL:
method of the
UIApplication
class. For example, to open the Google homepage in the Safari application, you could write this:
NSURL *url = [NSURL URLWithString:
@"http://google.com"];
[[UIApplication sharedApplication]
openURL:url];
The
http://
part here is called a URL scheme and identifies the application you want to launch.
URL schemes exist for several of the other native iPhone applications and can be used to launch them in a similar manner.
For example, to launch the Mail application
A
, you can use this:
NSURL *url = [NSURL URLWithString:
@"mailto:[email protected]?subject=
test"];
[[UIApplication sharedApplication]
openURL:url];
To launch the SMS application, you can write this:
NSURL *url = [NSURL URLWithString:
@"sms:555-1234"];
[[UIApplication sharedApplication]
openURL:url];
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To dial a phone number, you can use the following:
NSURL *url = [NSURL
URLWithString:@"tel: //555-1234"];
[[UIApplication sharedApplication]
openURL:url];
To launch the Maps application and search for pizza
B
, you can use this:
NSURL *url = [NSURL URLWithString:
@"http://maps.google.com/maps?q=
pizza"];
[[UIApplication sharedApplication]
openURL:url];
You can also use a URL scheme to launch your own application.
To create an application with a custom URl scheme:
1. Create a new view-based application, saving it as URLSchemeExample.
2. In the Xcode Groups & Files pane, expand the Resource section, and select the <app>-Info.plist file.
3. Right-click the Information Property List key, and select Add Row. Select “URL types” from the list
C
.
4. Expand Item 1, right-click URL identifier, and again select Add Row. Select URL
Schemes from the list
D
.
B
Launching the Maps application and finding some pizza.
C
Adding a URL type.
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E
Setting the name of the URL scheme.
5. Select Item 1, and set the value to myapplication
E
.
6. Open
URLSchemeExampleView
Controller.m
, uncomment the
viewDidLoad
method, and write the following:
[self.view setBackgroundColor:
[UIColor redColor]];
7. Build and run your application.
You should see a blank, red screen.
Your application doesn’t do anything at the moment, but by running it (which installs the application on the iPhone or simulator), you have just registered the new URL scheme (
myapplication
) created in step 5.
8. You can now launch this application from a different application by using the following code:
NSURL *url = [NSURL URLWithString:
@"myapplication:"];
[[UIApplication sharedApplication]
openURL:url];
Sharing information between applications
When you launch an application using a
URL scheme, the entire URL is passed to the application. This is how Safari knew to open the Google Web page in the earlier example.
To capture the URL, you need to implement the
application:didFinishLaunchingWith
Options:
method within the application delegate. The
launchOptions
parameter of this method is a dictionary whose contents will contain both the URL and an identifier for the source application that launched your application.
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To respond to being launched via a URl scheme:
1. Open the URLSchemeExampleApp
Delegate.m file, and add the
application: didFinishLaunching
WithOptions:
delegate method.
if (launchOptions) {
NSString *sourceApp =
[launch Options objectForKey:
UIApplicationLaunchOptions
Source ApplicationKey];
NSURL *url = [launchOptions
objectForKey:UIApplication
Launch OptionsURLKey];
NSString *msg = [NSString
stringWithFormat:@"sourceApp:
%@, url: %@",sourceApp,url];
}
UIAlertView *alert =
[[UIAlertView alloc]
initWithTitle:@"" message:msg
delegate:self
cancelButtonTitle:@"OK"
otherButtonTitles:nil];
[alert show];
[alert release];
[self applicationDidFinish
Launching: application];
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F
The application displaying the
launchOptions
values.
You first check to see whether the
launch Options
dictionary exists (it will be null if the application was launched normally), and then you extract two values from the dictionary:
UIApplicationLaunchOptionsSource
ApplicationKey
contains the bundle identifier for the source application that opened your application.
UIApplicationLaunchOptionsURLKey
contains the complete URL (including the URL scheme itself).
For testing, you then create an alert view and display these values. In a realworld application, you could parse the
URL to extract any information passed to your application.
2. Build and run the application to install it onto the iPhone or simulator.
Code Listing 3.2 shows the updated code.
3. Again, switch to the other application, and change your code to this:
NSURL *url = [NSURL URLWithString:
@"myapplication:message=
helloworld"];
[[UIApplication sharedApplication]
openURL:url];
Your application will launch, and you should see an alert message similar to
F
.
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Code Listing 3.2 The updated code to respond to being launched by a URL scheme.
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Using the pasteboard
Another useful way of passing information between applications is by using the pasteboard . Items copied to the pasteboard from one application can be copied from the pasteboard by another application.
You can get a reference to the pasteboard by writing this:
UIPasteboard *pasteboard =
[UIPasteboard generalPasteboard];
You can then place a string on the pasteboard by using this:
pasteboard.string = @"Hello World";
After launching your app via a call to
openURL:
, you can then retrieve the string from the pasteboard by writing this:
UIPasteboard *pasteboard =
[UIPasteboard generalPasteboard];
NSString *myString =
pasteboard.string;
The
UIPasteboard
class contains convenience properties like this for
NSString
,
UIImage
,
NSURL
, and
UIColor
.
You can add multiple items to the pasteboard by using the
setItems:
method. For example, to add two strings to the pasteboard, you can use this:
UIPasteboard *pasteboard =
[UIPasteboard generalPasteboard];
NSDictionary *item1 = [NSDictionary
dictionaryWithObject:@"Hello World"
forKey:@"public.utf8-plain-text"];
NSDictionary *item2 = [NSDictionary
dictionaryWithObject:@"Goodbye
World" forKey:@"public.utf8-
plain-text"];
NSArray *items = [NSArray arrayWith
Objects:item1,item2,nil];
[pasteboard setItems:items];
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Each item is first added to an array as a dictionary and then added to the pasteboard using the
setItems:
method. You can later retrieve this array from the pasteboard using the
items
property.
The key for each dictionary is a uniform type identifier (UTI). For a list of available
UTIs, refer to Uniform Type Identifiers
Overview in the developer documentation.
Code Listing 3.3 shows the code updated to retrieve a string from the pasteboard and display it in an alert view.
Code Listing 3.3 The code updated to use the pasteboard.
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iPhone User interface Elements
iOS offers a rich set of buttons, sliders, switches, and other user interface elements for you to use in creating your applications.
These elements can be roughly divided into two main groups, views and controls.
Views provide the primary canvas and drawing functionality of your user interface.
They also give your application the ability to handle touch events.
Controls extend upon this functionality and provide a way for users to interact with your application by defining what is known as the target-action mechanism: the ability for a control to send an action (method call) to a target (object) when an event
(touch) occurs.
In this chapter, you’ll look at the various views and controls available in iOS and examine how to use them.
All the examples use the View-based Application template, with the code running in the view controller.
In This Chapter
Views
Image Views
Scrolling
Labels
Progress and Activity Indicators
Alerts and Actions
Picker Views
Toolbars
Text
Web Views
Controls
142
146
152
156
164
112
126
129
136
139
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Views
A view is the common name given to instances of
UIView
. You can think of a view as your application’s canvas; in other words, if you are adding UI elements to your iPhone’s interface, you are adding them to a view. All the UI elements discussed in this chapter are themselves subclasses of
UIView
and so inherit its properties and behavior.
The root level of your iPhone application interface consists of a single
UIWindow
to which you would typically add one or more views to work with, instead of using
UIWindow
directly.
Since
UIView
is a subclass of
UIResponder
, it can receive touch events. For most views, you’ll receive only a single-touch event unless you set the
multipleTouchEnabled
property to
TRUE
. You can determine whether a view can receive touch events by modifying its
userInteractionEnabled
property. You can also force a view to be the only view to receive touch events by setting the
exclusiveTouch
property to
YES
.
(For more information on working with touch events, see Chapter 7, “Touches, Shakes, and Orientation.”)
You can also nest views within each other in what’s known as the view hierarchy.
Child views are known as subviews, and a view’s parent is its superview.
Frames
Views are represented by a rectangular region of the screen called a frame. The frame specifies the origin (x, y) and size
(width, height) of the view, in relation to its parent superview. The origin of the coordinate system for all views is the upper-left corner of the screen
A
.
Origin {0,0} subview superview subview subview
Height
Width
A
Child views (subviews) are nested inside their parent view (superview). A view’s origin is at the top-left corner.
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B
Adding a subview to the view controller’s main view.
C
Console output after moving the view. Notice that although the frame changes, the bounds remain the same.
Code Listing 4.1 Creating a new view.
To add a view to your application:
1. Create a
CGRect
to represent the frame of the view, and pass it as the first parameter of the view’s
initWithFrame:
method:
CGRect viewFrame = CGRectMake
(10,10,100,100);
UIView *myView = [[UIView alloc]
initWithFrame:viewFrame];
Here you are creating a view that is inset 10 pixels from the top left of its superview and that has a width and height of 100 pixels.
2. Since the view is transparent by default, set its background color before adding it to the view controller’s existing view
B
:
myView.backgroundColor =
[UIColor blueColor];
[[self view] addSubview:myView];
Code Listing 4.1 shows the completed code.
your
To improve performance, set
UIView
’s opaque wherever possible.
property to
YES
Bounds
A view’s bounds are similar to its frame, but the location and size are relative to the view’s own coordinate system rather than those of its superview. In the previous example, the frame’s origin is
{10,10}
, but the origin of its bounds is
{0,0}
. (The width and height for both the frame and the bounds are the same.)
The console output illustrates this
C
: After moving the view 25 pixels in the x direction (using the view’s
center
property), the frame origin is now
{35,10}
, whereas the bounds origin remains at
{0,0}
.
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Let’s say you want to create a view so that it completely fills its superview. A common mistake is to use the frame of the superview.
If you tried to run this code in your application, you’d see a gap at the top of the subview
D
.
Recall that, in the project, the
UIWindow
is at the top level. The
UIWindow
has two subviews: the status bar and the main view 20 pixels below
E
. The origin of the frame of the main view is actually
{0,20}
.
(Remember, a view’s frame is in relation to its superview’s coordinate system.)
The solution to this problem is to use the bounds of the superview (
Code Listing 4.2), which causes the view to correctly fill its superview.
You can use the function to convert a
NSStringFromCGRect()
CGRect
into an
NSString
, making it useful for logging
CGRect s to the console via
NSLog()
.
Other useful functions when dealing with
CGRect s are
NSStringFromCGPoint() and
NSStringFromCGSize()
.
D
Setting the frame incorrectly by using the frame of the superview. Notice the gap at the top.
Origin {0,0}
Origin {0,20}
Window status bar 20px view controller view
E
The enclosing
UIWindow
contains both the status bar and the view controller’s view as subviews. Notice how the controller’s view has an origin starting at
{0,20}
for its
frame
.
Code Listing 4.2 Initializing the view’s frame with its superview’s bounds.
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Animation
Many properties of a view can be animated, including its
frame
,
bounds
,
backgroundColor
,
alpha
level, and more.
You’ll now look at some simple examples that illustrate additional view concepts.
To animate your view:
1. Retrieve the center of the view controller’s main view:
CGPoint frameCenter =
self.view.center;
2. Create a view, set its background color, and, just as you did earlier, add it to the main view:
float width = 50.0; float height = 50.0;
CGRect viewFrame = CGRectMake
(frameCenter.x-width,
frameCenter.y-height,width*2,
height*2);
UIView *myView = [[UIView alloc]
initWithFrame:viewFrame]; myView.backgroundColor =
[UIColor blueColor];
[[self view] addSubview:myView];
Here you are positioning your view in the center of its superview and giving it a width and height of 50 pixels.
3. Set up an animation block:
[UIView beginAnimations:nil
context: NULL];
[UIView setAnimationDuration:1.0];
An animation block is a wrapper around a set of changes to animatable properties. In this example, the animation lasts for one second.
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4. Resize the view:
viewFrame = CGRectInset(viewFrame,
-width, -height);
[myView setFrame:viewFrame];
The
CGRectInset()
function takes a source rectangle and then creates a smaller or larger rectangle with the same center point. In this example, a negative value for the width and height creates a larger rectangle.
5. Close the animation block:
[UIView commitAnimations];
This will cause all of the settings within the animation block to be applied.
6. Build and run the application.
You should see the view grow in size over a period of one second.
Code Listing 4.3
shows the completed code.
Try changing the animation. setAnimationDuration: line to see how you can affect the speed of the
Code Listing 4.3 Animating a view.
Try setting some other properties on the view within the animation block (such as backgroundColor they have.
) to see what effect
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Animating multiple views without using an autoresizing mask. Notice how the new subview ends up in the top-left corner of its superview.
Autosizing
When a view changes size or position, you often want any subviews contained within the view to change size or position in proportion to their containing superview.
You can accomplish this by using a view’s autoresizing mask . Now let’s add a second subview inside the view you created in the previous exercise.
To add a subview:
1. Create a
CGRect
for the subview’s frame, again using the shortcut
CGRectInset()
function:
CGRect subViewFrame =
CGRectInset(myView.bounds,
width/2.0, height/2.0);
UIView *mySubview =
[[UIView alloc]
initWithFrame:subViewFrame]; mySubview.backgroundColor =
[UIColor yellowColor];
[myView addSubview:mySubview];
This time, the positive width and height values for the
CGRectInset
function make the new view smaller. To make them stand out, give it a different background color.
2. Build and run the application
F
. The new subview starts off in the center of its superview, but then it remains
“pinned” to its initial location as the animation progresses and ends up in the top-left corner.
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Code Listing 4.4 shows this code updated to use an autoresizing mask.
Notice how you set all four margins of the subview using the bitwise OR operator (the | symbol) between the constant values (
Table 4.1). Notice also that even though the animation is specified on the superview, the subview still animates automatically
G
.
3. You can visually set the
autoresizingMask
property in the size pane of the Inspector window in Interface Builder
H
.
Custom drawing
By default, the visual representation of a
UIView
is fairly boring. You can manipulate the size, background color, and alpha levels of the view, but not much else.
Luckily, it’s relatively simple to create your own
UIView
subclasses where you can implement custom drawing behavior. To see how this might be done, you’ll now learn how to create a
UIView
subclass with rounded corners.
G
Using the autoresizing mask property, the subview remains in the center of its superview during an animation.
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Setting the autoresizing mask in Interface Builder.
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Code Listing 4.4 Using an autoresizing mask.
TABle 4.1 Available autoresizingMask values
Value
UIViewAutoresizingNone
UIViewAutoresizingFlexibleLeftMargin
UIViewAutoresizingFlexibleWidth
UIViewAutoresizingFlexibleRightMargin
UIViewAutoresizingFlexibleTopMargin
UIViewAutoresizingFlexibleHeight
UIViewAutoresizingFlexibleBottomMargin
Description
The view does not resize.
The view resizes by expanding or shrinking in the direction of the left margin.
The view resizes by expanding or shrinking its width.
The view resizes by expanding or shrinking in the direction of the right margin.
The view resizes by expanding or shrinking in the direction of the top margin.
The view resizes by expanding or shrinking its height.
The view resizes by expanding or shrinking in the direction of the bottom margin.
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To create a custom rounded-corner view:
1. In Xcode, select File > New File. Create a new Objective-C class, making sure that “Subclass of” is set to UIView
I
.
Save the file as roundedCornerView.
2. Open roundedCornerView.m, and modify your code to look like Code Listing 4.5.
3. Open UITestViewController.m, and replace all instances of
UIView
with
roundedCornerView
. Don’t forget to also import the header file for roundedCornerView.h at the top of the file. Code Listing 4.6 shows the updated code.
4. Build and run your application to see the result with rounded corners for the views
J
.
As you can see, custom drawing happens in the
drawRect:
method of
roundedCornerView
. You set a couple of variables here—one to determine the width of the line you will be drawing and another to determine the color.
5. By setting the color to the superview’s background color, you are essentially
“erasing” any time you draw in the subview.
float lineWidth = 10.0;
UIColor *parentColor = [[self
superview] backgroundColor];
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I
Adding a custom class to draw the rounded corner view.
J
In the updated application, the views now have rounded corners.
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Code Listing 4.5 The
roundedCornerView
class.
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6. Now you get a reference to the current graphics context and set the pen color and width.
A graphics context is a special type that represents the current drawing destination, in this case the custom view’s contents.
CGContextRef ctx =
UIGraphicsGetCurrentContext();
CGContextSetStrokeColorWithColor
(ctx, parentColor.CGColor);
CGContextSetLineWidth(ctx,
lineWidth);
7. Finally, call a custom function that draws a line around the outside of the view, rounding at each corner:
CGContextStrokeCorners(ctx,rect);
Code Listing 4.6 Replacing regular views with the custom class.
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Transforms
You’ve already looked at resizing a view by increasing the width and height of its frame. Another way to perform the same task is by using a transform.
A transform maps the coordinates system of a view from one set of points to another.
Transformations are applied to the bounds of a view. In addition to scaling, you can also rotate and move a view using transforms.
To resize your view using a scale transform:
n
Add the following code to your application:
CGAffineTransform scale =
CGAffineTransformMakeScale
(2.0,2.0); myView.transform = scale;
This creates a scale transform, doubling both the width and the height of your view.
or
Transforms can also be used to move views by using a translate transform:
CGAffineTransform translate =
CGAffineTransformMakeTranslation
(50,50); myView.transform = translate;
This would cause a view to move by
50 pixels along both the x- and y-axes.
or
Finally, you can apply a rotation transform to rotate your views:
CGAffineTransform rotate =
CGAffineTransformMakeRotation
(radiansForDegrees(180)); myView.transform = rotate;
Because rotations are specified in radians, you use a function to convert from degrees.
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To apply both a rotation transform and a scale transform to your view:
1. Update the code to look like the following:
CGAffineTransform scale =
CGAffineTransformMakeScale
(2.0,2.0);
CGAffineTransform rotate =
CGAffineTransformMakeRotation
(radiansForDegrees(180));
CGAffineTransform myTransform =
CGAffineTransformConcat
(scale,rotate); myView.transform = myTransform;
Note how you can combine transformations using the
CGAffineTransform
Concat()
function.
Code Listing 4.7 shows the completed code.
2. Build and run your application
K
.
Your view should rotate and scale at the same time.
You no longer need to set the autoresizingMask property of the subview because the transform is applied to the view and its subviews at the same time.
You can return a view to its original state by setting its transform
property to
CGAffineTransformIdentity
.
K
The view both rotating and scaling.
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Code Listing 4.7 Rotating and scaling the view.
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Image Views
The
UIImageView
class extends
UIView
to provide support for displaying images.
Its default initializer,
initWithImage:
, takes a
UIImage
as its only parameter
( Code Listing 4.8):
UIImage *anImage = [UIImage
imageNamed:@"myImage.png"];
UIImageView *myImageView =
[[UIImageView alloc]
initWithImage:anImage];
Note that
initWithImage:
automatically adjusts the frame of the new image view to match the width and height of the image assigned
A
.
If you resize the image view, you can see that the image automatically scales to fit
B
:
CGSize viewSize =
myImageView.bounds.size;
//shrink width 50% viewSize.width = viewSize.width
* 0.5;
//keep height the same viewSize.height = viewSize.height;
CGRect newFrame = CGRectMake
(0,0,viewSize.width,
viewSize.height);
[myImageView setFrame:newFrame];
Code Listing 4.8 Creating an image view.
A
The image displaying a graphic.
B
Resizing the image view.
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C
Resizing the image view while maintaining its aspect ratio.
Code Listing 4.9 Animating over an array of images.
You can control scaling behavior by the
contentMode
property of
UIView
, which defaults to
UIViewContentModeScaleToFill
.
For example, to maintain the aspect ratio of the image, you would write this:
myImageView.contentMode =
UIViewContentModeScaleAspectFit;
In the resulting image, note that although the image itself is scaled, the image view still has the same bounds
C
. Any part of the bounds not rendered in the image will be transparent.
Animating images
UIImageView
lets you animate over an array of images, which is handy for creating progress animations.
Code Listing 4.9
shows the code updated to animate over three images.
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To animate over an image:
1. Create the image view, and set its frame:
CGRect viewFrame = CGRectMake
(0,0,200,200);
UIImageView *myImageView =
[[UIImageView alloc]
initWithFrame:viewFrame];
2. Create and set the image array:
NSArray *arrImages =
[[NSArray alloc] initWithObjects:
[UIImage imageNamed:
@"apple.png"],
[UIImage imageNamed:
@"apple2.png"],
[UIImage imageNamed:
@"apple3.png"],nil];
[myImageView
setAnimationImages:arrImages];
[arrImages release];
3. You can control the speed of the animation (in seconds) and number of times the animation is repeated. The default is
0
, making the animation loop indefinitely:
[myImageView
setAnimationDuration:0.5];
[myImageView setAnimation
RepeatCount:0];
4. To begin the animation, add the following:
[myImageView startAnimating];
5. To stop the animation, you call
stopAnimating
.
For simplicity, the previous examples use imageNamed:
to create the images. Although convenient, this method creates autoreleased objects that can’t be manually released in a lowmemory situation. So, it’s usually wiser to use something like the initWithContentsOfFile: method and manually allocate/release your images.
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Code Listing 4.10 Using a scroll view.
Scrolling
Often your views will be larger than the visible area, and you need a way to scroll. For this, you use the
UIScrollView
class.
A scroll view acts as a container for a larger subview, allowing you to pan around the subview by touching the screen. Vertical and horizontal scroll bars indicate the position in the subview.
Code Listing 4.10 shows an example of using a scroll view.
To create a scroll view:
1. Set the frame as usual:
CGRect scrollFrame = CGRectMake
(20,90,280,280);
UIScrollView *scrollView =
[[UIScrollView alloc]
initWithFrame:scrollFrame];
2. Create an image view, assigning it an image that is larger than the scroll view:
UIImage *bigImage = [UIImage
imageNamed:@"appleLogo.jpg"];
UIImageView *largeImageView =
[[UIImageView alloc]
initWithImage:bigImage];
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3. Add the image view to the scroll view, and set the
contentSize
property of the scroll view:
[scrollView addSubview:
largeImageView]; scrollView.contentSize =
largeImageView.frame.size;
This is an important step: If you don’t tell the scroll view how large its subview is, it won’t know how to scroll at all.
4. Finally, add the scroll view to the main view:
[self.view addSubview:scrollView];
You'll now see the scroll view with horizontal and vertical scroll bars indicating the current position in the image view
A
. You can hide these scroll bars using the
showsHorizontalScrollIndicator
and
showsVerticalScrollIndicator
properties.
If you play around with the previous code, you’ll notice that if you scroll quickly to the edge of the subview, the scroll view actually moves a little too far before springing back.
This behavior is controlled by the bounce
property. You can restrict bouncing to the x- or y-axis using the alwaysBounceHorizontal
and alwaysBounceVertical
properties, or you can disable it entirely by setting bounce
to
NO
.
Zoom
You can also zoom in and out of an image using a scroll view. The
minimumZoom-
Scale
and
maximumZoomScale
properties control the scale by which you can zoom in and out. By default, both of these properties are set to the same value (
1.0
), which disables zooming. You must implement one of the
UIScrollViewDelegate
methods to return the view that is being zoomed.
A
Using a scroll view to pan around a large image.
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B
The page control indicating the total number of pages and the current page as a series of dots at the bottom of the iPhone’s screen.
To enable zooming:
1. Add the
UIScrollViewDelegate
protocol in the controller.h file:
@interface UITestViewController :
UIViewController
<UIScrollViewDelegate>
2. Update the scroll view code to allow you to zoom out by
1/2
and in by
2x
:
scrollView.minimumZoomScale = 0.5; scrollView.maximumZoomScale = 2.0; scrollView.delegate = self;
You’ve also set the delegate to be the controller (
self
).
3. Implement the
viewForZoomingInScroll
View:
delegate method, and return the image view. Code Listing 4.11 shows the updated code.
Paging
Scroll views support the paging of their content—the ability to add multiple subviews as “pages” and then scroll between them as you might turn the pages of a book. Adding a
UIPageControl
will provide a visual depiction of your current page
B
.
Code Listing 4.11 Adding zoom to the scroll view.
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To create a page control:
1. Update the code to remove the image from the scroll view, and set some new properties:
float pageControlHeight = 18.0; int pageCount = 3;
CGRect scrollViewRect =
[self.view bounds]; scrollViewRect.size.height -=
pageControlHeight; myScrollView =
[[UIScrollView alloc]
initWithFrame:scrollViewRect]; myScrollView.pagingEnabled = YES;
The
pagingEnabled
property turns paging on for the scroll view.
2. Since you have three pages, set the
contentView
of the scroll view to be three times wider than its frame. You’ll also turn off the scroll view indicators:
myScrollView.contentSize =
CGSizeMake(scrollViewRect.size.
width * pageCount,1); myScrollView.showsHorizontal
ScrollIndicator = NO; myScrollView.showsVertical
ScrollIndicator = NO; myScrollView.delegate = self;
3. Set up the page control by creating a frame below the scroll view, and add a target to the page control so that when it is tapped, it will call the
changePage:
method:
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CGRect pageViewRect =
[self.view bounds]; pageViewRect.size.height =
pageControlHeight; pageViewRect.origin.y =
scrollViewRect.size.height; myPageControl = [[UIPageControl
alloc] initWithFrame:
pageViewRect]; myPageControl.backgroundColor =
[UIColor blackColor]; myPageControl.numberOfPages =
pageCount; myPageControl.currentPage = 0;
[myPageControl addTarget:self
action:@selector(changePage:)
orControlEvents:UIControlEvent
ValueChanged];
4. Call the
createPages
method by adding three
UIView
s side by side to the scroll view to represent the three pages.
5. Set the
backgroundColor
property of the views.
In a real-world application, these would be more interesting! At this stage, your scroll view will actually work, but you need some more work to get the page control to reflect the current page.
6. Implement the
scrollViewDidScroll
: delegate method:
CGFloat pageWidth = sender.frame.
size.width; int page = floor((sender.content
Offset.x - pageWidth / 2) /
pageWidth) + 1; myPageControl.currentPage = page;
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This simply does some math to calculate your current page during the scroll and then updates the page control accordingly.
7. Finally, implement the
changePage:
method called when the page control is tapped:
int page = myPageControl.
currentPage;
CGRect frame = myScrollView.frame; frame.origin.x = frame.size.width
* page; frame.origin.y = 0;
[myScrollView scrollRectToVisible:
frame animated:YES];
This scrolls the scroll view horizontally based on the page you have selected in the page control.
Code Listing 4.12
shows the completed code.
Code Listing 4.12 Implementing a page control.
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Code Listing 4.12 continued iPhone User Interface Elements
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labels
Instances of the
UILabel
class display a read-only view that can contain one or more lines of text. For example, to create a simple label and set its
text
,
font
,
textColor
, and
backgroundColor
properties ( Code Listing 4.13), use this:
myLabel.backgroundColor =
[UIColor clearColor]; myLabel.textColor =
[UIColor redColor]; myLabel.font = [UIFont
systemFontOfSize: 18.0]; myLabel.text = @"Hello World!";
By default, a label is rendered as black text on a white background. You can also set a font by name:
myLabel.font = [UIFont fontWithName:
@"Verdana" size:18.0];
Table 4.2 shows the available fonts you can use.
If you don’t specify a font size, the label will automatically reduce the font to fit the text within the label’s frame. You can control how small the font gets with the
minimumFontSize
property, and you can disable this behavior entirely with the
adjustsFontSizeToFitWidth
property.
To add a shadow to a label’s text, you could write the following:
myLabel.shadowColor =
[UIColor darkGrayColor]; myLabel.shadowOffset =
CGSizeMake(1.0,1.0);
The
shadowOffset
controls set how far on the x- and y-axes from the label’s text the shadow is drawn. The default is
{0,-1}
.
Code Listing 4.13 Creating a label.
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TABle 4.2 Fonts available on the iPhone
Family
American Typewriter
AppleGothic
Arial
Arial Hebrew
Arial Rounded MT Bold
Arial Unicode MS
Name
AmericanTypewriter, AmericanTypewriter-Bold
AppleGothic
ArialMT, Arial-BoldMT, Arial-BoldItalicMT, Arial-ItalicMT
ArialHebrew, ArialHebrew-Bold
ArialRoundedMTBold
ArialUnicodeMS
Courier
Courier New
DB LCD Temp
Courier, Courier-BoldOblique, Courier-Oblique, Courier-Bold
CourierNewPS-BoldMT, CourierNewPS-ItalicMT, CourierNewPS-BoldItalicMT,
CourierNewPSMT
DBLCDTempBlack
Geeza Pro
Georgia
GeezaPro-Bold, GeezaPro
Georgia-Bold, Georgia, Georgia-BoldItalic, Georgia-Italic
Hiragino Kaku Gothic ProN HiraKakuProN-W6, HiraKakuProN-W3
Heiti J
Heiti K
Heiti SC
Heiti TC
Helvetica
Helvetica Neue
Marker Felt
Times New Roman
Thonburi
Trebuchet MS
Verdana
Zapfino
STHeitiJ-Medium, STHeitiJ-Light
STHeitiK-Medium, STHeitiK-Light
STHeitiSC-Medium, STHeitiSC-Light
STHeitiTC-Light, STHeitiTC-Medium
Helvetica-Oblique, Helvetica-BoldOblique, Helvetica, Helvetica-Bold
HelveticaNeue, HelveticaNeue-Bold
MarkerFelt-Thin
TimesNewRomanPSMT, TimesNewRomanPS-BoldMT,
TimesNewRomanPS-BoldItalicMT, TimesNewRomanPS-ItalicMT
Thonburi-Bold, Thonburi
TrebuchetMS-Italic, TrebuchetMS, TrebuchetMS-BoldItalic, TrebuchetMS-Bold
Verdana-Bold, Verdana-BoldItalic, Verdana, Verdana-Italic
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The
textAlignment
property allows you to align the label text to the left (the default), center, or right.
The
lineBreakMode
property controls how a label wraps text that is too wide to fit within its frame. You can specify whether you want the text to be word or character wrapped, clipped, or truncated at the start, end, or middle of the text.
To display multiple lines of text in a label, use the
numberOfLines
property and the
\n
newline escape character:
myLabel.numberOfLines = 2; myLabel.text = @"Hello World\nSecond
line";
The height of the label’s
frame
property needs to be tall enough to accommodate the number of lines of text you specify, or the text will be wrapped using the value defined in the
lineBreakMode
property
(
Code Listing 4.14).
Setting the to line count.
numberOfLines
property
0
will make the label dynamically set the
Code Listing 4.14 Setting various properties of a label.
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A
A progress view at 33 percent completion.
Progress and
Activity Indicators
When performing tasks that may take some time, you often need to provide some kind of visual feedback to your users. If you know how long the task will take to complete, you can use a progress indicator to show the user how much of the task has been performed and how much still has to run. If you are unable to determine the duration of the task, use a “busy” indicator (such as the beach ball or hourglass on OS X).
iOS provides classes for showing both progress and activity.
Indicating progress
When you want to show the progress of a task, use
UIProgressView
, a very simple class, consisting of only two properties.
You create a progress view and set its style using the
initWithProgressViewStyle:
method:
UIProgressView *myProgressView =
[[UIProgressView alloc]
initWithProgressViewStyle:
UIProgressViewStyleDefault];
The indicator appears as a horizontal bar that fills from left to right to show completion
A
. This is controlled by the
progress
property, using a value between
0.0
(not started) and
1.0
(completed):
[myProgressView setProgress:0.33];
Although you set the frame of the progress view, the maximum height of a progress view is 9 pixels, so any larger value will be ignored. iPhone User Interface Elements
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Code Listing 4.15 shows an example of using
UIProgressView
with the progress updated in a timer to simulate a long- running task.
The other progress bar style,
UIProgress ViewStyleBar
, also uses a horizontal bar indicator but is more suitable for using in a toolbar (explained in the following section).
Showing activity
For tasks of an indeterminate duration, you can use the
UIActivityIndicatorView
class, represented by an animated “spinner” graphic
B
.
Code Listing 4.15 Updating the progress view.
B
An activity indicator view.
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Code Listing 4.16 Creating an activity indicator view.
Similar to a progress view, you can create an activity indicator using the
initWithActivityIndicatorStyle:
method:
UIActivityIndicatorView
*myActivityView =
[[UIActivityIndicatorView alloc]
initWithActivityIndicatorStyle:
UIActivityIndicatorViewStyleWhite];
The default size of an activity view is a
21-pixel square. If you use the
UIActivity
IndicatorViewStyleWhiteLarge
style, this increases to a 36-pixel square.
Unlike the progress view, however, the frame property controls both the height and the width of the view. For activity views larger than 36 pixels, it’s best to use the larger style so the image won’t become pixelated.
The activity view will initially be invisible. Calling the
startAnimating
method shows the activity view and causes the spinner graphic to animate:
[myActivityView startAnimating];
Calling
stopAnimating
will stop the spinner animation, but you need to remember to set the
hidesWhenStopped
property if you want the activity view to hide (
Code Listing 4.16).
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Alerts and Actions
Often in your applications you’ll want to present a message to your users. Perhaps you want to alert them about an error or present them with options for a given action. As an iPhone developer, you handle these situations using alert views and action sheets .
Alerting users
To display an alert message, use the
UIAlert View
class. You define a
title
,
message
, and
delegate
, and then you configure buttons to be shown in the view.
To display an alert view:
1. First, create a simple alert view
A
:
UIAlertView *myAlert =
[[UIAlertView alloc]
initWithTitle:@"title"
message:@"message"
delegate:nil
cancelButtonTitle:@"OK",
otherButtonTitles:nil]
[myAlert show];
2. Using the
otherButtonTitles
property, you can create the same alert view with up to four additional buttons
B
:
UIAlertView *myAlert =
[[UIAlertView alloc]
initWithTitle:@"title"
message:@"message"
delegate:nil
cancelButtonTitle:@"OK"
otherButtonTitles:@"button1",
@"button2", @"button3",
@"button4",nil];
A
A bare-bones alert view.
B
An alert view with several buttons added.
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Using the dismissWithClickedButton
Index:animated: method, you can programmatically close an alert view without the user having to tap a button. This might be useful in a situation where you want to show an alert for a short time and then hide it automatically.
Code Listing 4.17 Display an alert view.
If you have only two buttons in your alert view, they will be displayed side by side. Otherwise, buttons are added from top to bottom, with the cancel button always being at the very bottom.
If you don’t need the message or title text, there is room for five buttons in addition to the cancel button.
3. You can add buttons after creating your alert view by using the
addButtonWith
Title:
method:
[myAlert addButtonWithTitle:
@"new button"];
4. To determine which button is tapped, set the delegate, and implement the
alertView:clickedButtonAtIndex:
delegate method (
Code Listing 4.17).
The
buttonIndex
parameter tells you which button was tapped, starting with the cancel button at index 0. Alert views close automatically when a button is tapped.
Another way to alert the user is by making the iPhone vibrate by calling the function
AudioServicesPlayAlertSound
(kSystemSoundID_Vibrate)
. You’ll need to add the
AudioToolbox project for this to work.
framework to your
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Confirming an action
When presenting the user with a number of options, you can use a
UIActionSheet
.
To create an action sheet:
1. An action sheet is created in a similar way to an alert view
C
:
UIActionSheet *mySheet =
[[UIActionSheet alloc]
initWithTitle:@"Do you really
want to delete?" delegate:nil
cancelButtonTitle:@"No"
destructiveButtonTitle:@"Yes"
otherButtonTitles:nil];
[mySheet showInView:self.view];
2. Define titles for three types of button.
The cancel button is generally used to dismiss the action sheet.
The destructive button acts as the confirmation of the action and is usually shown in red to indicate its importance.
The other buttons are similar to the alert view and allow you to add more buttons.
Setting any of these parameters to
nil
prevents the button type from showing.
3. Set the delegate, and implement the
actionSheet:clickedButtonAtIndex:
method, which is called when a button is tapped.
You can compare the
buttonIndex
parameter to the action sheet’s
cancelButtonIndex
and
destructiveButtonIndex
properties to determine which button was tapped.
Code Listing 4.18 shows the code updated with some of these options.
C
An action sheet is “pinned” to the bottom of the screen, and it contains only a title.
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Code Listing 4.18 Adding more options to the action sheet.
Action sheets vs. alert views
Action sheets are functionally similar to alert views, with a number of important differences:
.
Action sheets are attached to a view. The code used in the previous exercise attaches the action sheet to the controller’s main view.
.
.
You can optionally show the alert sheet from a tab bar or a toolbar using the
showFromTabBar:
and showFromToolbar: methods.
Action sheets do not have a
message
property; they have a single title property.
.
You can change how the action sheet looks by using the
actionSheetStyle
property. In addition to the default style, you can give your action sheet a black transparent or opaque style.
Setting the style to UIActionSheetStyleAutomatic will give your action sheet the same appearance as the bottom bar if one exists.
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Picker Views
The
UIPickerView
class allows users to
“spin” a wheel-type control to select one or more values. Each picker view consists of one or more components consisting of one or more rows. Each component can be spun independently of the others. For example, the picker view can be used to select a date value with three components in the control, representing the month, day, and year
A
.
The number of components and rows in a picker view is determined by its datasource , an object that adopts the
UIPickerViewDataSource
protocol. The display and selection of the picker view content is handled by the delegate, which adopts the
UIPickerViewDelegate
protocol (the datasource and the delegate can be the same object).
To create a simple picker view:
1. Add the protocol declarations to your interface definition:
@interface UITestViewController :
UIViewController
<UIPickerViewDataSource,
UIPickerViewDelegate>
2. Create a picker view, and add it to the main view (
Code Listing 4.19):
CGRect pickerFrame =
CGRectMake(0,120,0,0);
UIPickerView *myPicker =
[[UIPickerView alloc]
initWithFrame:pickerFrame]; myPicker.dataSource = self; myPicker.delegate = self;
[self.view addSubview:myPicker];
A
A picker view being used to select a date.
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Picker views are always 320 pixels by
216 pixels in size and cannot be resized.
3. The
showsSelectionIndicator
property creates a translucent bar across the control to indicate the selected row.
4. At a minimum, you need to implement two data source methods.
numberOfComponentsInPickerView:
returns the number of segments or components in the picker view. In this example, you want a single component, so return the value
1
.
pickerView:numberOfRowsInComponent:
returns the number of rows for each component. Again, ignore the component parameter (since you have only a single component), and return the number of rows.
continues on next page
Code Listing 4.19 A bare-bones picker view implementation.
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5. Implement the delegate
pickerView: titleForRow:forComponent:
method, returning an
NSString
representation of the current row
B
:
return [NSString stringWithFormat:
@"Row %i",row];
The picker view can display much more interesting data than this simple example.
Components can be of different widths and, rather than just simple text, can actually have entire views embedded within them
C
.
To enhance the picker view:
1. After calling the
initComp1
and
initComp2
methods to create some sample data, update the
numberOfComponentsInPickerView:
method to return two components
(one for each of the sample arrays).
Also, update the
pickerView:numberof
RowsInComponent:
method to return the size of each array:
if (component == 0) return [comp1 count]; else return [comp2 count];
The arrays here contain different numbers of elements; in other words, components do not need the same number of rows.
2. Define a new delegate method,
picker
View:widthFormComponent:
, and set the widths of the components to different values:
if (component == 0) return 100.0; else return 200.0;
B
The picker view shows the sample data.
C
The updated picker view. Not only do the two components display different content, but they also have different widths and numbers of items.
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Code Listing 4.20 The updated picker view.
3. Implement the
pickerView:viewForRow: forComponent:reusingView:
delegate, returning either an image view or a label. This method allows you to embed almost any view subclass in a picker view component.
4. Finally, in the
pickerView:didSelectRow: inComponent:
delegate, log the selected row and component to the console.
When you spin the picker view, this method isn’t fired until the scrolling animation ends.
Code Listing 4.20 shows the updated code.
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Code Listing 4.20 continued
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Picking dates and times
iOS also has a special version of a picker,
UIDatePicker
, geared toward picking dates as well as times. The datePickerMode property determines the style of the picker
D
.
Since the date picker is localized, it will automatically display dates and times in the format of the device locale. You can, however, override these settings to display dates and times for other locales.
You can set properties for start and end dates
(for the date-style pickers) and for minute and countdown values (for the time-style pickers).
UIDatePicker
is not actually a subclass of
UIPickerView
. It is a UIControl subclass that has a custom UIPickerView as a subview.
This means that you use the target-action mechanism to manage the selection of values.
As with other controls, you set the action:
D
A date picker with the default style of
UIDatePickerModeDateAndTime lets you pick both the date and the time.
[myPicker addTarget:self action:@selector(pickerChanged:) forControlEvents:
UIControlEventValueChanged];
The date picker creates a UIControlEventValueChanged event when a date or time is selected
( Code Listing 4.21).
Code Listing 4.21 Implementing a date picker.
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Toolbars
You can create toolbars in iPhone applications using the
UIToolbar
class. A toolbar usually spans the entire width of the display and is aligned to either the top or the bottom of the screen
A
.
To create a toolbar:
1. As with many other views, you can create a toolbar with the
initWithFrame:
method. Use the size of the main view to calculate the y position of the toolbar.
This is important since you may not know the orientation of the iPhone and want the toolbar to sit at the bottom of the screen.
CGSize viewSize =
self.view.frame.size; float toolbarHeight = 44.0;
CGRect toolbarFrame = CGRectMake
(0,viewSize.height-toolbarHeight,
viewSize.width,toolbarHeight);
UIToolbar *myToolbar =
[[UIToolbar alloc] initWithFrame:
toolbarFrame];
2. Set the
autoresizingMask
property of the toolbar to ensure that it stays in the same position (in this case, aligned to the bottom of the screen) even if the user rotates their iPhone.
myToolbar.autoresizingMask =
UIViewAutoresizingFlexible
Width | UIViewAutoresizing
FlexibleLeftMargin | UIView
AutoresizingFlexibleRight
Margin | UIViewAutoresizing
FlexibleTopMargin;
A
Most of the controls sit on the toolbar in Safari.
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B
A toolbar showing the three toolbar item styles for the
initWithTitle:style:target:action:
method.
C
Some of the available system item styles.
3. You can change the color and translucency of the toolbar using the
tintColor
and
translucent
properties:
myToolbar.tintColor =
[UIColor redColor]; myToolbar.translucent = YES;
Toolbar items
Buttons you add to a toolbar are known as toolbar items and are created using the
UIBarButtonItem
class. Several types of buttons are available, and you can create them in several ways: n n n n
The simplest way to create a button with some title text is by using the
initWithTitle:style:target:action:
method
B
. Use the
target
and
action
parameters to indicate which method to call when the button is pressed.
Similarly, the
initWithImage:style: target:action:
method lets you create a button with an image instead of text.
The button will automatically resize its width to that of the image.
You can create a button from your own custom
UIView
subclass using the
initWithCustomView:
method.
However, you must set the
target
and
action
properties manually.
The final way is to use the
initWithBar
ButtonSystemItem:target:action:
method. iOS offers a set of predefined buttons, known as system items, to ensure your application adheres to the iPhone interface guidelines. Use them whenever possible.
There are system items for play, pause, and stop buttons, as well as for search, trash, and camera
C
. For a complete list of system items available, refer to the
UIBarButtonSystemItem
type in the developer documentation.
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You will often use two particular system item types:
UIBarButtonSystemItemFlexibleSpace
and
UIBarButtonSystemItemFixedSpace
.
Both are not visible and represent spaces on a toolbar. The flexible-space item lets you force a button to the other side of the toolbar, while the fixed-space item simply lets you add a space between buttons. You can set the
width
property of a fixed-space item to determine how wide you want the space to be.
Once you’ve created these buttons, add them to an
NSArray
and then use the
setItems:
method of the
UIToolbar
to add them to the toolbar itself. The optional
animated:
parameter allows you to have buttons fade in as they are added to the toolbar.
Code Listing 4.22 shows the updated code, with buttons of various types and a flexible-space item being used to push a button to the right side of the toolbar. If you try rotating the phone, you will notice that the toolbar and buttons correctly align themselves regardless of orientation
D
.
D
The toolbar has correctly sized itself with the iPhone in landscape mode. The trash toolbar item is aligned to the right.
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Code Listing 4.22 Creating several different types of toolbar items.
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Text
For entering text into your applications, iOS provides two classes,
UIText Field
and
UITextView
. Both allow the user to enter and edit text using an onscreen keyboard and support features such as cut/copy and paste, spell check, and more, but the two classes function differently.
To create a text field:
1. You can use the
UITextField
class to enter small amounts of text, such as user names, passwords, or search terms. This field is limited to a single line of text.
2. As with most other views, you use the
initWithFrame:
method to create them:
CGRect textRect = CGRectMake
(10,10,300,20);
UITextField *myTextField =
[[UITextField alloc]
initWithFrame:textRect]; myTextField.backgroundColor =
[UIColor whiteColor];
This also sets the background color of the text field; otherwise, it’s transparent by default. Text fields also don’t have a border by default.
3. Use the
borderStyle
property to choose from four different styles
A
.
The
UITextBorderStyleRoundedRect
style has a white background and will ignore the
backgroundColor
property.
If you set a custom
UIImage
as the
background
, the
borderStyle
property will be ignored.
4. You can set the text font, color, and alignment to apply to the entire text field.
Text fields do not support the styling of individual text elements.
A
Border styles available for text fields.
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B
Press the clear button to remove any text in the text field.
C
Clicking the clear button removes any text in the text field.
Two of the keyboards available by setting the
keyboardType
property of a text field.
5. You can set your text field to automatically resize the font to accommodate larger text:
myTextField.font =
[UIFont systemFontOfSize:22.0]; myTextField.adjustsFontSizeTo
FitWidth = YES; myTextField.minimumFontSize = 2.0;
This example sets the initial font size as
22 and then tells the text field to automatically shrink the font to a minimum size of 2 if the text is wider than the text field’s bounds.
6. Setting the
clearsOnBeginEditing
property to
YES
will clear any existing text when you first touch the control:
myTextField.clearsOnBeginEditing =
YES; myTextField.clearButtonMode =
UITextFieldViewModeWhileEditing;
The
clearButtonMode
property adds a small button to the end of the text field, letting you clear the text at any time
You can determine when this button
B
. is shown, such as only when editing the text.
To use keyboards:
1. Tap in the text field to open a keyboard from the bottom of the screen.
2. You can choose from a number of keyboard styles
C
, each designed for particular situations such as entering numbers or using a web browser.
3. Set the style with the
keyboardType
property.
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4. To disable this function, set the
autocorrectionType
property to
UITextAutocorrectTypeNo
.
5. Set the
autocaptializationType
property to determine whether the keyboard capitalizes your typing by word, sentence, or even all characters.
6. You can change the text on the Return key via the
returnKeyType
property.
7. Use the
enablesReturnKeyAutomatically
property to determine whether the
Return key is enabled even if you haven’t entered any text into the text field.
In
Code Listing 4.23, the
secureTextEntry
property is set to
YES
, which is useful for text fields that contain passwords or other sensitive information. As you enter text, you will see only the last letter typed.
8. You may have noticed that the keyboard doesn’t disappear when you press the
Return key. To hide the text field, you must implement the
textFieldShould
Return:
delegate and tell the text field to resign its first responder status:
[textField resignFirstResponder]; return YES;
Code Listing 4.23 Creating a secure text field.
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9. Similarly, you can make the keyboard appear automatically when the view is loaded by setting the first responder status in the
viewDidLoad:
method:
[myTextField
becomeFirstResponder];
10. To prevent the keyboard from showing at all, which is useful if you are implementing your own custom keyboard, return
NO
from the
textFieldShould
BeginEditing:
delegate method.
For a complete list of keyboard options, refer to the “UITextInputTraits Protocol” section of the developer documentation.
Restricting content
You can also use the delegate methods to control the text being entered into the text field. The
textField:shouldChange
CharactersInRange:replacementString:
delegate is called whenever the text is changed. You could, for example, use this method to restrict the number of characters entered. Code Listing 4.24 shows a text field that allows a maximum of ten characters.
Code Listing 4.24 Limiting the contents of a text field to ten characters.
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You should check the length of the replacement rather than just looking at the length of the text in the text field, since the text field’s contents can be altered via copy and paste as well as by using the keyboard.
For the same reason, simply changing the keyboard type to numeric does not guarantee that a user will enter only numeric values (since a user could paste non-numeric values into the field).
Code Listing 4.25
shows the same delegate method, this time restricting the text field to allow numeric values only.
Text views
The
UITextView
class allows for multiline editable text. Although similar to text fields, text views feature a number of important differences.
Text views don’t have any support for automatically reducing the font size like text fields have. Also, they don’t have any support for clearing the text other than through programmatically setting the
text
property. There is also no support for secure text entry.
As with text fields, text views also apply the same text style to the entire text. Apple recommends using a
UIWebView
(see the
“Web Views” section) if you require multiple styles in your text.
Code Listing 4.25 Restricting the contents of a text field to numeric values.
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D
A text view with an active data detector.
Data detectors
Text views can analyze their contents and convert any links or phone numbers into tappable links by using a capability known as data detectors . Tapping the link will either launch the browser or call the phone number.
Two data detector types are available:
UIData DetectorTypePhoneNumber
for phone numbers and
UIDataDetectorTypeLink
for Web
http:
links. To enable both, set the
data DetectorTypes
property:
myTextView.dataDetectorTypes =
UIDataDetectorTypeAll;
There’s one caveat with data detectors:
The default behavior of text views is to show the keyboard when tapped, so you can’t tap the link of a data detector. For data detectors to work, you must set the
editable
property of the text view to
NO
.
In
D
, the URL is underlined just as it would be in a web browser. Tapping it will launch the Safari application.
Hiding the keyboard
A text view’s keyboard behaves the same as a text field, with one important difference: Since a text view supports multiline editing, pressing the Return button on the keyboard will insert a carriage return instead of calling a delegate method. Just as with the text field, resign the text view’s first responder status to hide the keyboard when you have finished editing the text.
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Scrolling the interface
You may have noticed that since the iPhone’s keyboards are very large, they take up a lot of the screen and can overlap other controls when shown. It would be handy if your interface moved up when the keyboard appeared and then moved back down once it disappeared.
You can make that happen by placing the controls inside a
UIScrollView
. When the keyboard appears, you simply scroll everything up, scrolling back down when the keyboard hides.
To scroll the interface in response to the keyboard:
1. Create and add a scroll view, making it the full size of the main view:
CGRect viewRect =
[self.view bounds]; myScrollView = [[UIScrollView
alloc] initWithFrame:viewRect]; myScrollView.contentSize =
viewRect.size;
[self.view
addSubview:myScrollView];
2. Add the controls to the scroll view instead of the main view (since you want them to scroll).
3. Implement the
textViewDidBeginEditing:
delegate method, which is called when the keyboard is shown.
Here you need to calculate both the bottom of the text view and the top of the keyboard and then tell the scroll view to scroll the difference. You must also look at the
orientation
property of the iPhone because the keyboard will have a different height in portrait mode than in landscape mode.
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4. Implement the
textViewDidEndEditing:
delegate so that when the keyboard is hidden, you scroll the text view to its original position.
Code Listing 4.26 shows the completed code.
Code Listing 4.26 Scrolling an interface in response to a keyboard.
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Web Views
Just as with iPhone’s native Safari application, you can display web-based content in your own applications by using the
UIWebView
class. (In fact, Safari on the iPhone uses a
UIWebView
for display.)
Web views provide touch-based control for zooming in and out of pages, panning, and scrolling. Tapping links can load pages, and tapping in text controls will open a keyboard for data entry.
To display a web page in your application:
1. Just as with other views, you can add web views to your interface in the usual way:
CGRect webRect = CGRectMake
(10,10,300,400);
UIWebView *myWebView =
[[UIWebView alloc]
initWithFrame:webRect]; myWebView.scalesPageToFit = YES;
The
scalesPageToFit
property ensures that larger pages are zoomed out or in enough to fit correctly in the current frame as well as letting you zoom in and out in response to pinch gestures.
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A
A web view displaying the Google homepage.
2. Use the
loadRequest:
method to load content into the web view, which takes an
NSURLRequest
object as its only parameter:
NSURL *url = [NSURL URLWithString:
@"http://www.google.com"];
NSURLRequest *request =
[NSURLRequest requestWithURL:url];
[myWebView loadRequest:request];
[self.view addSubview:myWebView];
This would load the Google homepage
A
.
3. If your page is taking a long time or you want to cancel loading, use the
stopLoading
method. You can also check the
loading
property to make sure the page is actually in the process of loading.
What’s the status?
Web views provide four optional delegate methods that will notify you about changes in the status of loading a web page:
webView:shouldStartLoadWithRequest:navigationType:
is sent before the web view begins to load the content and is a handy place to handle navigation within your web views (see the
“Loading local content and handling hyperlinks” section).
webViewDidStartLoad:
is sent when your web page starts loading and is a good place to show a progress indicator.
webViewDidFinishLoad:
is sent when the web view finishes loading a page and is a good place for you to stop a progress indicator. This will not be sent if the page fails to load for any reason.
webView:didFailLoadWithError:
is sent if an error occurs in loading the web page.
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If you are building a web browser–type interface with Forward and Backward buttons, you can use the
canGoForward
and
canGoBackward
properties to determine whether your buttons should be enabled, and you can use the
goForward
and
goBackward
methods to navigate through the web view’s page history.
Although there is no direct access to the page history, you can easily maintain history via the delegate methods mentioned in the “What’s the status?” sidebar.
Code
Listing 4.27 shows the code updated to include an activity indicator when the page is loading.
Code Listing 4.27 Implementing a web view.
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Running JavaScript
You can execute JavaScript in a web view by using the
stringByEvaluatingJavaScript
FromString:
method. For example, if you wanted to open an alert dialog box in your web view, write the following:
[webView stringByEvaluating
JavaScript FromString:@"alert
('Hello World!);"];
This lets you manipulate your web page’s style sheet or DOM or even call existing
JavaScript functions defined within the page itself. For example, to change the background color of your web page, you could write the following:
[webView stringByEvaluating
JavaScript FromString:
@"document.bgColor= \"#000000\";"];
To call the JavaScript function
myFunction
defined in the web page, you could use this:
[webView stringByEvaluating
JavaScript FromString:
@"myFunction();"];
For performance reasons, any JavaScript you call must execute fully within ten seconds and must be less than 10MB in size.
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loading local content and handling hyperlinks
You can also use web views to display local content, such as an .html file that ships in your application bundle. This makes web views handy for displaying content that mixes graphics with text or requires multiple text styles. (Remember that
UILabel
s and
UITextView
s are restricted to only a single style per control.)
To load content from a local file:
1. Use the
loadHTMLString:baseURL:
method to load content contained in the resources folder of the application bundle:
myWebView.scalesPageToFit = NO;
NSString *htmlPath =
[[NSBundle mainBundle]
pathForResource:@"myPage"
ofType:@"html"];
NSString *htmlContent =
[NSString stringWithContents
OfFile:htmlPath encoding:
NSUTF8StringEncoding error:nil];
[myWebView loadHTMLString:
htmlContent baseURL:nil];
This time,
scalePageToFit
has been set to
NO
because you don’t want the user to be able to zoom in and out of the web view as if it were a web page
B
.
2. To prevent a user from tapping any hyperlinks in the document, you can set
userInteractionEnabled
to
NO
for the web view. This also disables the ability to scroll content that may be longer than the control can fit on the screen at once.
or
B
A web view displaying some local content, including a hyperlink to another page.
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When implementing this type of functionality, it’s common to warn the user they are navigating away from your application and have them confirm the action. You can do this with the this chapter.
UIAlertView
described in the exercise, “To display an alert view,” earlier in
Code Listing 4.28 Capturing clicks on a web view.
To disable links entirely, return
NO
from the
webView:shouldStartLoadWith
Request:navigationType:
delegate method.
3. To open a link in the native Safari application, you could write the following in the
webView:shouldStartLoadWithRequest: navigationType:
delegate method
(
Code Listing 4.28):
NSURL *pageURL = [request URL]; if ( ([[pageURL scheme]
isEqualToString: @"http"]) &&
(navigationType == UIWebView
NavigationTypeLinkClicked ))
[[UIApplication sharedApplication]
openURL:pageURL]; return NO;
Here you are trapping only
http:
links.
Other link types, such as
https:
, would have no effect.
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Controls
Almost all the drawing functionality you’ve learned about so far also applies to controls. Most controls inherit their class from
UIControl
, and
UIControl
is a subclass of
UIView
A
; this is how controls know how to draw themselves.
You’ll never actually create instances of
UIControl
directly the way you do with
UIView
.
UIControl
is simply used to define a common set of functionality and behavior for its subclasses.
As mentioned at the beginning of this chapter, controls use the target-action mechanism to respond to touch events.
Since the iPhone is a Multi-Touch device, many different events can occur, such as tapping, multitapping, dragging, and releasing. Luckily, each control has been designed to respond to only those events appropriate for its usage, and each does so in an intuitive and consistent manner.
You’ll now take a closer look at the controls available to iPhone developers.
Buttons
When adding buttons to your application, you’ll use the
UIButton
class
B
.
The default initializer for buttons is the
buttonWithType:
method:
UIButton *myButton =
[[UIButton buttonWithType:
UIButtonTypeRoundedRect];
NSObject
UIResponder
UIView
UIControl
A
The
UIControl
class hierarchy.
B
The default button types for
UIButton
.
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To be notified when a button changes state, add a target and action:
[myButton addTarget:self action:
@selector(buttonClick:)
forControlEvents:UIControlEvent
TouchUpInside];
The
UIControlEventTouchUpInside
event is most commonly used for handling regular button presses.
The
UIButtonTypeCustom
type lets you create buttons with images or even draw them yourself using your own custom drawing code (as discussed earlier in the
“Views” section).
To create a button with an image:
1. Specify an image for the button’s default state using
NSControlStateNormal
:
UIImage *buttonImage =
[UIImage imageNamed:
@"myButtonImage.png"];
[myButton setImage:buttonImage
forState:UIControlStateNormal];
UIButton
will automatically apply highlight effects to indicate that the button is pressed or disabled.
2. You can also set multiple appearance properties for each of these states, including the title text, font, and color.
You can use different images for the four different states: the default (as shown in step 1), highlighted, selected, and disabled. This enables you to create buttons to represent other controls.
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To create a checkbox button:
1. Assign images for both of the buttons’ states:
[checkbox setImage:[UIImage
imageNamed:@"checkbox_off.png"]
forState:UIControlStateNormal];
[checkbox setImage:[UIImage
imageNamed:@"checkbox_on.png"]
forState:UIControlStateSelected
];
2. Set the target method to call when the button is tapped:
[checkbox addTarget:self action:
@selector(checkboxClick:)
forControlEvents:UIControlEvent
TouchUpInside];
3. In the
checkboxClick:
method, simply flip the button’s
selected
property:
btn.selected = !btn.selected;
Since you’ve previously defined images for the two different states, the button automatically updates to display the correct image. Code Listing 4.29 shows the updated code.
If you specify an button type other than image
or title
for any
UIButtonTypeRounded
Rect
, the button effectively becomes a button of
UIButtonTypeCustom
.
Switches
Switches, represented by the
UISwitch
class, let you create an on/off control
C
.
To create a switch:
1. Use the
initWithFrame:
method:
CGRect switchRect = CGRectMake
(120,50,0,0);
UISwitch *mySwitch = [[UISwitch
alloc] initWithFrame:switchRect];
Code Listing 4.29 Creating a check box.
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C
Switches are used extensively in the Settings application of the iPhone.
UISwitchSlider
UIImage
View
UIImage
View
UIView
UILabel
(“ON”)
UILabel
(“OFF”)
UIImage
View
D
The control hierarchy that makes up a
UISwitch
.
Since switches are always the same size, the width and height properties are ignored.
2. When you change a switch’s value, it generates a
UIControlEventValueChanged
event:
[mySwitch addTarget:self action:
@selector(switchAction:)
forControlEvents:UIControlEvent
ValueChanged];
3. To turn a switch on/off, call the
setOn:Animated:
method:
[mySwitch setOn:YES animated:YES];
Switches don’t have any properties for modifying the default visual appearance, but with a little digging, you can control a couple of elements.
Within the control hierarcy of a
UISwitch
, the “on” and “off” elements are
UILabels
D
. You can manipulate the text, font, color, and more.
To alter the appearance of a switch:
1. To retrieve the two
UILabel
s within the switch that hold the switch’s text , you can use this:
UIView *mainView = [[[[mySwitch
subviews] objectAtIndex:0]
subviews] objectAtIndex:2];
UILabel *onLabel = [[mainView
subviews] objectAtIndex:0];
UILabel *offLabel = [[mainView
subviews] objectAtIndex:1];
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2. Now you can change the text and color of these labels. The choice of text values is quite limited since the labels are small in size and are clipped by their containing view:
onLabel.text = @"YES"; offLabel.text = @"NO"; onLabel.textColor =
[UIColor yellow Color]; offLabel.textColor =
[UIColor green Color];
3. When setting the text values, you should localize your replacement text wherever possible.
Code Listing 4.30
shows the updated code.
Code Listing 4.30 Customizing the switch control.
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E
The brightness slider control indicates the change in value with graphics at both ends of the control.
F
A custom slider control.
Sliders
Although switches have only two possible states, sliders let you select from a range of values on a horizontal bar, or track, with a thumb indicator that can be moved from side to side to select values
E
.
Unlike the
UISwitch
, there’s quite a lot you can do to customize the visual appearance of sliders, such as putting images to represent the values at either end of the track.
You can also customize the thumb image and the graphics that appear on the track on both sides of the thumb as the values change
F
.
Just as with the
UISwitch
, sliders create a
UIControlEventValueChanged
event when their value is changed. By setting the
continuous
property, you can choose to have these events fired either as the slider is changed or at the end of a change.
Code
Listing 4.31 demonstrates this with a custom
UISlider
, with minimum, maximum, and thumb images. In the
sliderAction:
method, you are forcing a “step” behavior, making the slider jump to the next value in increments of ten. A label added to the view displays the current slider value.
Although not specified in the developer documentation, setting the thumb image of a
UISlider
also hides the tracking image.
You must also set the minimum and maximum track images.
The stretchableImageWithLeft
CapWidth:topCapHeight: method lets you create an image that can stretch in the center but does not stretch on either side, as shown in the rounded edges of the track images.
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Code Listing 4.31 Implementing a custom slider.
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G
A segment control.
Code Listing 4.32 Creating a segment control.
Segmented controls
The
UISegmentedControl
consists of a horizontal control divided into segments
G
. Segmented controls are useful for allowing users to pick from a group or set of values.
Each segment functions as its own button. By default, selecting a segment will deselect the others in the control (much as a radio button does in HTML). You can alter this behavior by setting the
momentary
property.
To create a segmented control:
1. Create an array of
UIImage
s or
NSString
s, and then call the default initializer
initWithItems:
(
Code Listing
4.32).
2. Set the frame, and the control will automatically resize to accommodate its segments.
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3. Set the width of individual segments using the
setWidth:forSegmentIndex:
method.
This will automatically resize any other segments that have not had their widths explicitly set to fit within the control.
4. Select segments using the
setSelected
SegmentIndex:
method.
5. Disable individual segments using the
setEnabled:forSegementAtIndex:
method.
6. Add more segments using
insertSegments WithImage:atIndex: animated:
or
insertSegmentsWithTitle:atIndex: animated:
.
7. Set the
animated
property to
YES
so your segments will “slide in” as they are added.
8. To remove segments, use the
remove
SegmentsAtIndex:animated:
method.
9. Use
removeAllSegments
to clear the entire control.
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Segment control styles
Segment controls have three different styles, which can be set using the segmentedControlStyle property
H
.
Set the style to UISegmentedControlStyleBar to change the color of the control via the tintColor property, but depending on the color you use, you may not be able to see the difference between selected and unselected.
Code Listing 4.33 shows an example of how to use some of the properties of a segmented control.
Use the UISegmentControl to create a “glass” alternative to a UIButton. Use the tintColor property to change the color of the button.
H
The three styles available for segmented controls.
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Tabs and Tables
At the core of most iPhone applications, the view controller classes allow you to manage the visual elements that make up your application’s interface in a consistent fashion while eliminating redundant code. View controllers are the C in the MVC design pattern, providing the layer between your data model and your user interface.
In this chapter, you’ll see how to work with these classes. You’ll start by looking at the base
UIViewController
class from which the other view controller classes inherit and see how it provides a lot of the core functionality required by any iPhone application. Then you’ll see how you can add a tab-based interface using the
UITabBarController
class.
Finally, you’ll investigate how to use the
UITableViewController
and
UINavigationController
classes to present tabular, hierarchical data.
In This Chapter
View Controllers
Tab Views
Table Views
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View Controllers
The
UIViewController
class is the main class used to control most views (a view being a single screen within your application) and provides the base class for the
UITabBarController
and
UINavigation
Controller
classes discussed later in this chapter.
Each view controller has a single main view—represented by the
view
property— which it alone owns. Main views cannot be shared between view controllers. The main view will generally have one or more subviews containing the actual content of your application (other views, controls, and user-interface elements). For more information on views, see Chapter 4, “iPhone User
Interface Elements.”
These are a view controller’s main responsibilities: n
To manage the presentation of its views, responding to events such as changes in the iPhone’s orientation or low-memory situations n
To act as the coordinator between the user interface and the application’s data model (See the “Model View Controller” section in Chapter 1, “Objective-C and
Cocoa,” for more information.)
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Presenting views
As mentioned, each view controller contains a main view that you would normally use as the canvas for your application’s user interface. You can put your code in a number of places when working with view controllers: n
loadView
—Although you should not call this method directly, if you create your own views manually, then you should override this method and assign them to the view controller’s
view
property.
n n
viewDidLoad
—This method is called just after the view controller loads its views into memory and is a good place for you to perform any additional initialization. Many of the code examples in this book use this method as the point at which to create the user interface.
viewDidUnload
—Conversely, this is called when the view controller releases its views from memory and is a good place for you to clean up any objects you may have created within the view controller.
n n
viewWillAppear:
—This is called when the view is about to be added to a window and is not yet visible. It’s a good place to perform any customization such as changing the view’s orientation. If you implement any code in this method, make sure you also call
[super viewWillAppear:]
.
viewDidAppear:
—This is called when the view has been added to a window and is a good place to place code that needs to run after the view has been presented. If you implement any code in this method, make sure you also call
[super viewDidAppear:]
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n
viewWillDisappear:
—This is called when the view is about to be removed from a window and is a good place for you revert to any changes that may have been made when
viewWillAppear:
was called. If you implement any code in this method, make sure you also call
[super viewWillDisappear:]
.
n
viewDidDisappear:
—This is called when the view is dismissed, covered, or hidden from view. If you implement any code in this method, make sure you also call
[super viewDidDisappear:]
.
Code Listing 5.1 shows an example of changing the background color and adding a button to the main view within the
viewDidLoad
method.
Responding to changes in orientation
Another responsibility of a view controller is to respond to changes in the iPhone’s orientation and automatically rotate the interface where appropriate. The
shouldAutorotateToInterfaceOrientation:
method is called immediately after the iPhone is rotated. If you want to autorotate to all four orientations (up, down, left, and right), you can simply return
YES
from this method. Otherwise, you can examine the
interfaceOrientation
property and return
YES
or
NO
based on the device’s current orientation.
Code Listing 5.1 Adding a button to the main view within the
viewDidLoad
method.
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To create an application that responds to changes in orientation:
1. Create a new view-based application, saving it as OrientationExample.
2. Open the OrientationExampleView
Controller.h file, and create an instance variable to display the orientation
( Code Listing 5.2).
3. Switch to the OrientationExampleView
Controller.m file, uncomment the
viewDidLoad
method, and add the following:
CGRect labelFrame = CGRectMake
(10,10,300,38); orientationLabel =
[[UILabel alloc]
initWithFrame:labelFrame]; orientationLabel.textAlignment =
UITextAlignmentCenter; orientationLabel.autoresizingMask =
UIViewAutoresizingFlexibleWidth; orientationLabel.text =
[self getOrientationName];
[self.view addSubview:
orientationLabel];
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Code Listing 5.2 The header file of the orientation example.
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You first create a label that spans the width of the screen. Notice how you set the text alignment of the label to be centered so that when the iPhone is rotated, your text will remain in the center of the label. Likewise, you set the
autoresizingMask
property so that the label stretches its width automatically when the iPhone is rotated from portrait to landscape mode. Finally, you call a method to set the text of the label.
4. Implement the
getOrientationName
method:
switch (self.interfaceOrientation)
{ case UIInterfaceOrientation
Portrait: return @"Portrait"; break; case UIInterfaceOrientation
PortraitUpsideDown: return @"Portrait (upside
down)"; break; case UIInterfaceOrientation
LandscapeLeft: return @"Landscape (left)"; break; case UIInterfaceOrientation
LandscapeRight: return @"Landscape (right)"; break;
}
This method looks at the current orientation of the iPhone (via the view controller’s
interfaceOrientation
property) and returns a descriptive string.
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Several methods are available for you to track changes in orientation: willRotateToInterfaceOrientation: duration:
—This is called just before rotation takes place. It’s a good place for you to pause any activity that may be happening in the user interface and to disable the ability for the user to interact with the application until the interface has completed rotating.
willAnimateRotationToInterface
Orientation:duration: —This is called with the rotation animation block itself and is a good place for you to write custom code to override the default rotation animation. For example, you could change the rotation to a cross-dissolve animation. didRotateFromInterface
Orientation:
—This is called once the rotation has completed and is a good place for you to reenable your user interface and reallow user interactions with your application if you disabled them earlier.
5. Next, implement the
didRotateFrom
InterfaceOrientation:
method:
orientationLabel.text =
[self getOrientationName];
This method is called just after the orientation of the iPhone changes. Here you simply update the label text.
6. Uncomment the
shouldAutorotateTo
InterfaceOrientation:
method, and add the following code:
return YES;
This will allow your interface to be autorotated in any direction.
7. Build and run the application.
If you rotate your iPhone, the label should automatically rotate and continue to fill the width of the screen.
The text should also change to indicate the iPhone’s current orientation. Try changing the allowed orientations by modifying the
shouldAutorotateTo
InterfaceOrientation:
method.
Code Listing 5.3 shows the completed code.
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Code Listing 5.3 The completed orientation example.
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A
Adding a second view controller class.
Code Listing 5.4 The header file of the flip modal example.
Displaying modal views
You display a view modally by presenting one view controller from another view controller. Modal views are animated onto the screen, and you can determine an animation type to use. This can be helpful in providing meaning to the action you are performing. For example, it’s common to provide settings for an application by “flipping” the settings view over the main view.
To display a view modally using a “flip” animation:
1. Create a new view-based application, saving it as FlipModalExample.
2. Select File > New, and add a new
UIViewController
subclass.
Save the file as FlipViewController.m.
Make sure that “Also create
‘FlipController.h’” is selected
A
.
3. Open the FlipModalExampleView
Controller.h file, import the header file, and create an instance variable to hold the flip view controller (
Code
Listing 5.4).
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4. Switch to the FlipModalExampleView
Controller.m file, uncomment the
view
DidLoad
method, and add the following:
flip = [[FlipController alloc]
init];
UIButton *viewButton = [UIButton
buttonWithType:UIButtonType
Rounded Rect];
CGRect buttonFrame = CGRectMake
(110,10,100,38);
[viewButton setFrame:buttonFrame];
[viewButton setTitle:@"Show"
forState:UIControlStateNormal];
[viewButton addTarget:self action:
@selector(buttonClick:)
forControlEvents:UIControlEvent
TouchUpInside];
[self.view addSubview:viewButton];
Here you create the flip controller and then add a button to your main controller view.
5. Implement the
buttonClick:
method:
flip.modalTransitionStyle =
UIModalTransitionStyleFlip
Horizontal;
[self presentModalViewController:
flip animated:YES];
Setting the
modalTransitionStyle
property of your flip controller to
UIModalTransitionStyleFlipHorizontal
uses a “flip” animation when the new view controller is shown modally.
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When presenting a view modally, you can pick from three animation styles:
UIModalTransitionStyleCover
Vertical is the default style and slides the view from the bottom to over the current view.
UIModalTransitionStyleFlip
Horizontal
is the style used in the example here and flips the view from right to left.
UIModalTransitionStyleCross
Dissolve fades the current view out and the new view in using a cross-dissolve.
All three of these styles perform the reverse animation when the view is dismissed.
6. Switch to FlipController.m, uncomment the
viewDidLoad
method, and add the following:
[self.view setBackgroundColor:
[UIColor redColor]];
UIButton *viewButton =
[UIButton buttonWithType:
UIButtonTypeRoundedRect];
CGRect buttonFrame = CGRectMake
(110,10,100,38);
[viewButton setFrame:buttonFrame];
[viewButton setTitle:@"Hide"
forState:UIControlStateNormal];
[viewButton addTarget:self action:
@selector(buttonClick:)
forControlEvents:UIControlEvent
TouchUpInside];
[self.view addSubview:viewButton];
This is almost the same code as with your main view controller, but you set the background of the view to make it obvious which view is showing.
7. Implement the second
buttonClick
: method:
[self dismissModalViewController
Animated:YES];
This tells the main view controller to hide the flip controller. The message is automatically forwarded to the main view controller (since it is the one dismissing the modal view). This is handy since it means you don’t have to declare any public methods or create a reference to the parent view controller.
8. Build and run the application.
Pressing Show will cause the view to flip and show the other view controller’s view modally. Pressing Hide will flip the view back.
Code Listing 5.5 shows the completed code.
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Code Listing 5.5 The completed flip modal application.
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Code Listing 5.5 continued
Handling low-memory conditions
View controllers can automatically handle low-memory scenarios by releasing and cleaning up any views that aren’t needed, such as when a view doesn’t have a superview. When a memory warning is issued
(via the
UIApplication
delegate), each view controller also receives a notification via the
didReceiveMemoryWarning
method. You can override this method to perform any memory cleanup within your own code. However, if you do so, make sure you also call
[super didReceive
MemoryWarning]
. You can also put your cleanup code in the
viewDidUnload
method, which will be called if the view controller decides it can release its views.
Since you would normally have multiple view controllers in your application, each with their own views and subviews, this provides a very granular memory management model where you can determine what you should release and when.
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Tab Views
You can use the
UITabBarController
class to create a multipage interface. Pages are displayed by selecting a tab from a tab bar at the bottom of the screen
A
.
Each page of the tab bar controller is a view controller. When a tab is selected, the view of the corresponding view controller is displayed above the tab bar.
To create an application with tabs:
1. Create a new view-based application, saving it as TabExample.
2. Select File > New, and add a new
UIViewController
subclass.
Save the file as Tab1Controller.m. Make sure that “Also create ‘Tab1Controller.h’” is selected
B
.
3. Repeat step 2, adding two more
UIViewController
subclasses named
Tab2Controller
and
Tab3Controller
.
4. Open TabExampleViewController.h, import the three tab controllers, create instance variables to represent the three tabs, and change the class name to
UITabBarController
(
Code Listing 5.6).
A
The World Clock application uses tabs to switch between clock types.
B
Adding a new
UIViewController
subclass.
Code Listing 5.6 The header file for the tab example.
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What happens if I have too many tabs?
In the exercises in this section, you added only a limited number of tabs to the tab bar. If you were to add so many that the tab bar ran out of room, a new special More tab would appear on the right edge of the tab bar
C
. Selecting this allows the user to customize the tab bar by choosing which tabs they want to display. You can restrict which tabs the user can edit by removing the corresponding view controller from the array in the customizableViewControllers property.
C
The More tab.
5. Switch to TabExampleViewController.m, uncomment the
viewDidLoad
method, and add the following code:
tab1 = [[Tab1Controller alloc]
init]; tab2 = [[Tab2Controller alloc]
init]; tab3 = [[Tab3Controller alloc]
init];
NSArray *arrTabs = [NSArray array
WithObjects:tab1,tab2,tab3,nil];
[self setViewControllers:arrTabs
animated:YES];
Here you create three tabs, add them to an array, and then assign them to the
viewControllers
property, which will create a tab for each element.
6. Switch to Tab1Controller.m, uncomment the
viewDidLoad
method, and add the following code to set the background color:
[self.view setBackgroundColor:
[UIColor redColor]];
7. Repeat step 6 for Tab2Controller.m and
Tab3Controller.m. Make sure you use a different color each time.
8. Build and run your application.
You should see a tab bar with three tabs. As you select a tab, the area above the tab bar will change color.
You can select a tab in your code by using the selectedIndex
property of the
UITabBarController
. This can be useful when you are developing your application, allowing you to launch your application on the page on which you are currently working.
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Adding graphics and titles to tabs
Although this example showed you how easy it is to create an application with tabs, the tabs themselves are not particularly helpful. It would be much better if each one had a title or graphic on it so that you knew what it actually did. Luckily,
UIViewController
has a property called
tabBarItem
that is designed for exactly this purpose.
To update the application to use tab bar items:
1. Open Tab1Controller.m, and create an
init:
method:
UITabBarItem *tab = [[UITabBarItem
alloc] initWithTitle:@"Tab 1"
image:nil tag:0];
[self setTabBarItem:tab];
[tab release];
Here you create a new tab item and set its title only.
2. Open Tab2Controller.m, and again create an
init:
method:
UITabBarItem *tab = [[UITabBarItem
alloc] initWithTabBarSystemItem:
UITabBarSystemItemFavorites
tag:1];
[self setTabBarItem:tab];
[tab release];
This time you are using the
initWithTab
BarSystemItem:
method to create the tab item. The iPhone has a number of system tabs that can be used for common functionality and are used in many of the built-in applications. Using a system item adds both a graphic and a label to the tab. For more information on the available system items, refer to the UITabBarItem Class Reference in the developer documentation.
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D
The completed tab example application.
3. Open Tab3Controller.m, and create a third
init:
method:
UITabBarItem *tab = [[UITabBarItem
alloc] initWithTitle:@"Tab 3"
image:nil tag:2];
[tab setBadgeValue:@"New!"];
[self setTabBarItem:tab];
[tab release];
Just as in step 1, you set a title, but no graphic, for the tab. However, this time, you also set the
badgeValue
property.
This will add a red oval to the upperright corner of your tab. This technique is commonly used to alert a user to a change in the contents of the tab.
4. Build and run the application
D
.
Code Listing 5.7 and Code Listing 5.8 show the completed code.
In this example, you created the tab bar item in the in the because init: viewDidLoad
method instead of
method. You did this viewDidLoad
is not actually called until the view controller displays its view, which would mean that the tab would not draw its contents until it had been selected.
You can use the delegate of a UITabBar
Controller (which must implement the
UITabBarControllerDelegate protocol) to disable tabs by implementing the tabBarCon troller:shouldSelectViewController: method and returning NO.
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Code Listing 5.7 The implementation files for the three tab view controllers.
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Code Listing 5.7 continued
Code Listing 5.8 The tab bar controller implementation file.
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Table Views
Table views—represented by the
UITableView
class—are the main interface element used to display lists and hierarchical data on the iPhone. Table views are used everywhere; the Settings, Clock,
Notes, Mail, and Contact applications all use table views as the main interface element.
Tables views represent their data in rows and sections. A row is an individual item in the table view. Rows can be grouped into zero or more sections. Sections can have both a header and a footer
A
.
The content of a row is called a cell and is represented by the
UITableViewCell
class.
You can use a cell’s
textLabel
and
detail
TextLabel
properties for displaying text, and you can use its
imageView
property for displaying images. Several different styles of cell exist, and you can also create your own custom cells.
To use a table view, you must implement a data source and, optionally, a delegate.
The data source provides the table view with its contents and determines what (if anything) can be edited. The delegate manages the selection and editing of rows and the display of section information.
Several of the delegate and data source methods have an
NSIndexPath
as a parameter. Using the
section
and
row
properties of this object is how you determine exactly to what in your table view you are referring.
A
The various elements of a table view.
Section header
Rows
Section footer
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B
Creating a navigation-based application.
Although you could create and add a table view much as you do with any other view, all the examples in this section use the
UITableViewController
class, which is designed specifically to manage a table view. Table view controllers are already configured as both the data source and the delegate of their own table view, and they have some additional functionality for updating a navigation bar when editing a table view.
To create an application with a table view:
1. Create a new navigation-based application, saving it as TableViewExample
B
.
2. Open RootViewController.h, and create the instance variable you will use to hold your table contents:
NSArray *arrCountries;
3. Switch to RootViewController.m, uncomment the
viewDidLoad
method, and add the following code:
self.title = @"Countries"; arrCountries = [[NSArray alloc]
initWithObjects: @"Australia",
@"Canada",@"Germany",@"France",
@"Great Britain",@"Italy",
@"Japan",@"New Zealand",
@"United States",nil];
Here you are setting the title of the toolbar and creating an array of country names.
4. Edit the
tableView:numberOfRowsIn
Section:
method to look like this:
return [arrCountries count];
This method is how the table view knows how many rows it should display.
In this example, you return the size of your array.
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5. Update the
tableView:cellForRowAt
IndexPath:
method to look like the following:
static NSString *CellIdentifier =
@"Cell";
UITableViewCell *cell =
[tableView dequeueReusable
CellWithIdentifier:
CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell
alloc] initWithStyle:
UITableViewCellStyleDefault
reuseIdentifier:Cell
Identifier] autorelease];
}
// Configure the cell.
cell.textLabel.text =
[arrCountries objectAtIndex:
indexPath.row];
NSString *imageName =
[NSString stringWithFormat:
@"%@.png",[arrCountries
objectAtIndex:indexPath.row]]; cell.imageView.image = [UIImage
imageNamed:imageName]; return cell;
Most of this code is unchanged from the template—you need to implement only the cell contents. Here you set the text by looking at the current row of the table and retrieving that value from your countries array. You also set an image for the cell; the image is a PNG file with the same name as the country.
You will need to add a PNG graphic for each country’s flag to your project. You can easily find these by visiting http:// images.google.com
.
C
The table view application.
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You may have noticed in tableView:cell
ForRowAtIndexPath: you gave your cell an identifier and used the dequeue
ReusableCellWithIdentifier: method when you created the cell. For performance reasons, each unique type of cell is stored in a reuse queue. You can then check this queue to see whether a cell is available for reuse, rather than creating a new one.
Code Listing 5.9 The code for the table view application.
6. Build and run the application.
You should see a list of countries with flags next to them
C
.
Code Listing 5.9 shows the completed code.
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Grouping rows into sections and styles
As mentioned earlier, you can group your table view’s rows into sections, which can be useful for displaying sets of related information. When using sections, it’s also common to use the grouped style for your table view, which is the style used in the
Settings application
D
. This style represents cells as rounded rectangles with a shaded background.
To update the application to use sections and a grouped table view:
1. Open the RootViewController.h file, and modify the code to create three instance variables ( Code Listing 5.10):
NSArray *arrAsiaPacific;
NSArray *arrEurope;
NSArray *arrNorthAmerica;
This time you are going to split the countries into three sections.
2. Switch to RootViewController.m, and update the
viewDidLoad
method:
arrAsiaPacific = [[NSArray alloc]
in itWithObjects:@"Australia",
@"Japan",@"New Zealand",nil]; arrEurope = [[NSArray alloc]
initWithObjects:@"Germany",
@"France",@"Great Britain",
@"Italy",nil]; arrNorthAmerica = [[NSArray
alloc] initWithObjects:@"Canada",
@"United States",nil];
Here you are creating an array for each section of your table view.
D
The Settings application uses the grouped table style.
Code Listing 5.10 The header file for the grouped table view application.
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3. Update the
tableView:numberOfRowsIn
Section:
method to look like this:
switch(section)
{ case 0: return [arrAsiaPacific count]; break; case 1: return [arrEurope count]; break; case 2: return [arrNorthAmerica count]; break; default: return 0; break;
}
This checks which section is being requested and then returns the size of the corresponding array.
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4. Similarly, you need to update the
tableView:cellForRowAtIndexPath:
method to check the correct array when you are creating the table view cell:
NSString *country; switch(indexPath.section)
{ case 0: country = [arrAsiaPacific
objectAtIndex:indexPath.row]; break; case 1: country = [arrEurope
objectAtIndex:indexPath.row]; break; case 2: country = [arrNorthAmerica
objectAtIndex:indexPath.row]; break;
}
NSString *imageName = [NSString
stringWithFormat:@"%@.png",
country]; cell.imageView.image = [UIImage
imageNamed:imageName]; cell.textLabel.text = country; return cell;
5. Update the
numberOfSectionsInTable
View:
method to return the correct number of sections:
return 3;
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E
Setting the table view style in Interface Builder.
F
The grouped table view application.
6. Implement the
tableView:titleFor
HeaderInSection:
method to create the title text above each section:
switch(section)
{ case 0: return @"Asia Pacific"; break; case 1: return @"Europe"; break; case 2: return @"North America"; break; default: return nil; break;
}
7. Update the style of your table view using Interface Builder
E
.
Since the property is read-only, you can’t edit it through code.
8. Build and run your application.
You should now see your data grouped into three sections
F
.
Code Listing 5.11 shows the updated code.
Just as you added text above each table section, implementing the tableView:title
ForFooterInSection:
method lets you add text below each section. You can also add any
UIView
subclass at the top and bottom of your table view by setting the and tableFooterView tableHeaderView
properties.
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Code Listing 5.11 The code for the grouped table view application.
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Code Listing 5.11 continued
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editing and searching table views
Now you’ll take a closer look at some of the data source methods you can use to edit your table view. You’ll see how you can drag the table view rows to reorder them, as well as how to delete rows. You’ll also add a
UISearchBar
control to the table view and write some code to allow you to filter the table view contents.
To create an editable table view that can be searched:
1. Create a new navigation-based application, saving it as EditTableViewExample.
2. Repeat steps 1–6 from the earlier exercise “To create an application with a table view.”
3. Open RootViewController.h, and create some new instance variables
( Code Listing 5.12).
Notice that you have changed the countries array to a mutable array. This is necessary since you will be changing the contents of the array when you search, edit, and delete items.
Code Listing 5.12 The header file for the editable table view application.
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4. Switch to RootViewController.m, and modify the
viewDidLoad
method:
arrTemp = [arrCountries mutable
Copy];
You first create a new array, copying the countries array. This is going to be used as temporary storage when you filter the table view by searching.
CGRect tableFrame =
[self.tableView frame];
CGRect searchRect = tableFrame; searchRect.size.height = 40; search = [[UISearchBar alloc]
initWithFrame:searchRect]; search.delegate = self; self.tableView.tableHeaderView =
search;
Next you create a search bar and attach it to the top of the table view by assigning it to the
tableHeaderView
property.
self.navigationItem.rightBarButton
Item = self.editButtonItem;
Then you set the navigation bar’s right button to be the control that edits the table view. The
editButtonItem
automatically switches your table view between edit modes.
searchDoneButton =
[[UIBarButtonItem alloc]
initWithBarButtonSystem
Item:UIBarButtonSystemItemDone
target:self action:@selector
(searchDone:)];
Finally, you create a bar button that you will use for searching.
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5. Implement the
tableView:canMoveRowAt
IndexPath:
method. By returning
YES
, you are allowing any row to be moved.
You can see which the user is attempting to move by looking at the
indexPath.row
property.
6. Implement the
tableView:moveRowAt
IndexPath:toIndexPath:
method that is called when the user rearranges a row:
NSString *name = [arrCountries
objectAtIndex:fromIndexPath.row];
[arrCountries removeObjectAtIndex:
fromIndexPath.row];
[arrCountries insertObject:name
atIndex:toIndexPath.row];
Although the table view will reorder itself, you also need to manually update the order of your countries array.
7. Implement the
tableView:commit
EditingStyle:forRowAtIndexPath:
method.
You check the editing style to see whether the user has deleted a row and, if so, remove it from the two arrays. You then call the
deleteRowsAtIndexPaths:with
RowAnimation:
method to remove the row from the table view using a fade animation.
8. Implement the
searchBarTextDidBegin
Editing:
delegate method:
self.navigationItem.rightBarButton
Item = searchDoneButton;
This method is called when the search keyboard appears. You swap the table view edit button with the search button you created earlier, allowing the user to exit from the search.
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9. Implement the
searchBarSearchButton
Clicked:
method, which is called when the user clicks “search” on the search keyboard.
This method calls a function that swaps the edit button in and hides the search bar keyboard.
10. Implement the
searchBar:textDid
Change:
method, which is called when the user starts typing in the search bar.
This in turn calls the
searchDone:
method:
NSString *searchFor = search.text;
[arrCountries release]; arrCountries = [arrTemp
mutableCopy]; if ([searchFor length] > 0) {
NSPredicate *pred =
[NSPredicate
predicateWithFormat:@"SELF
contains[c] %@",searchFor];
[arrCountries filterUsing
Predicate:pred];
}
[self.tableView reloadData];
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Here you reset the countries array so that you are dealing with the complete set of countries. You next create a predicate with the search text.
A predicate is a special object that allows you to perform filtering of data.
By calling the
filterUsingPredicate:
method of your countries array, you can filter the array to contain only the text entered in the search bar. Finally, calling
reloadData
tells your data to redraw itself, re-requesting all of its data using its data source methods. Since you have filtered the countries array, you will see only those countries that match the search text.
11. Build and run the application.
If you click the edit button, the table view will go into edit mode. You can reorder the rows by dragging using the handle on the right side of each row
G
.
Clicking the delete graphic on the left side of a row allows you to remove the row from the table view. If you tap in the search bar area, a keyboard will appear.
The data in the table view will be filtered as you type.
Code Listing 5.13
shows the completed code.
To prevent the delete button from appearing while still allowing the rows to be reordered, you can return
UITableView
CellEditingStyleNone
from the table
View:editingStyleForRowAtIndexPath: delegate method.
G
The editable table view application.
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Code Listing 5.13 The completed code for the editable table view application.
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Code Listing 5.13 continued
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H
A navigation controller with a navigation bar and a table view.
Navigation bar
Table view
Drilling down in table views
So far, the examples have presented a table view with only a single level of data.
It’s common, however, for data to be hierarchical, and you will often want to provide an interface where the user can select an item and then be presented with a subset of related items. This “drill-down” concept is used frequently and is surprisingly easy to implement using table views.
Before you see how to do this, it’s worth learning about another important class you will be using to add this functionality: the navigation controller.
A navigation controller, represented by the
UINavigationController
class, is a special type of view controller designed to help you navigate through hierarchical content known as the navigation stack. View controllers are pushed onto the navigation stack to display them and then popped off the navigation stack when you are finished with them.
Navigation controllers typically display a navigation bar at the top of the screen that indicates the current (topmost) controller on the stack. (You have actually been using a navigation controller in all the table view examples so far.) This bar will update as view controllers are pushed onto and popped off the navigation stack. This bar is also usually where any edit controls related to the view would sit. The view of the current view controller is displayed below this navigation bar
H
.
When combining a navigation-based interface with a tab bar, it is often the case that you’ll want to have the tab bar disappear when a view controller is pushed onto the navigation stack. You can accomplish this by using the hidesBottomBarWhenPushed property of the view controller.
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To create a table view with drill-down behavior:
1. Create a new navigation-based application, saving it as DrillDownExample.
2. Select File > New, and add a new
UIViewController
subclass
I
.
Save the file as DetailViewController.m.
Make sure that “Also create ‘DetailView
Controller.h’” is selected.
3. Open the DetailViewController.h file, change the class type to
UITableView
Controller
, and create a new property that you’ll use to hold the table view details ( Code Listing 5.14).
4. Switch to DetailsViewController.m, uncomment the
viewWillAppear
method, and add the following code:
self.title = @"Details";
[self.tableView reloadData];
Here you are setting the title and telling the table view to reload. Note that this time you are using the
viewDidAppear
method (instead of
viewDidLoad
as in the other exercises in this chapter).
This method will be run every time your details view is shown. By using the
reloadData
method call, you know your table view will always contain the correct data.
5. Implement the rest of this class as shown in Code Listing 5.15, which is the same code you used for previous exercises in this chapter.
6. Switch to RootViewController.h, import the DetailsViewController.h file, and create some instance variables that you will use to hold your table data and the details view ( Code Listing 5.16).
I
Adding a second view controller class to hold your table view details.
Code Listing 5.14 The header file for the drilldown details of the table view controller.
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Code Listing 5.15 The completed code for the drill-down details of the table view controller.
Code Listing 5.16 The main header file for the drill-down details application.
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7. Switch to RootViewController.m, uncomment the
viewDidLoad
method, and add the following code:
arrCountries = [[NSArray alloc]
initWithObjects: @"Australia",
@"United States",nil]; arrUSACities = [[NSArray alloc]
initWithObjects: @"Boston",
@"San Francisco",@"New York",
nil]; arrAustraliaCities = [[NSArray
alloc] initWithObjects:
@"Brisbane",@"Perth",@"Sydney",
nil]; details = [[DetailViewController
alloc] initWithStyle:UITableView
StyleGrouped];
Here you create three arrays: the first is your main array, and the other two are used for the details view. Notice that you can create the details view with a grouped style using the
initWithStyle:
method.
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J
The details screen of the drill-down table view application.
8. Implement the
tableView:didSelectRow
AtIndexPath:
delegate method that is called when you select a row:
if (indexPath.row == 0)
[details setContent:
arrAustraliaCities]; else
[details setContent:
arrUSACities];
[[self navigationController]
pushViewController:details
animated:YES];
Here you check which row the user has selected, assigning the appropriate array to the details view controller. You then push the view controller onto the stack of the navigation controller, causing it to be animated onto the screen.
9. The rest of the code is almost exactly as in previous exercises, except you set the
accessoryType
property when creating the cells:
cell.accessoryType = UITableView
CellAccessoryDisclosureIndicator;
This adds a disclosure triangle to the right side of the cell, providing a visual cue to the user that they will see detailed data by selecting the row.
10. Build and run your application
J
.
Selecting either row will cause the details view to be shown. Pressing the back button in the navigation bar will take you to the main screen.
Code List-
ing 5.17 shows the completed code.
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Code Listing 5.17 The completed drill-down table view application.
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Creating custom cells
So far, you’ve been using the default cell style in your table views (represented by the
UITableViewCellStyleDefault
type).
Four styles are available
K
.
However, you are not restricted to displaying text and images. You can create your own custom cell types to fully control the appearance and contents of the cell
L
.
Next you’ll learn how you can create a custom cell type that will allow you to add an on/ off switch and a button to your table view.
K
The four styles for table cells.
UITableViewCellStyleDefault
UITableViewCellStyleValue1
UITableViewCellStyleValue2
UITableViewCellStyleSubtitle
L
The Settings application makes extensive use of custom cells.
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To create a table view with custom cells:
1. Create a new navigation-based application, saving it as CustomCellExample.
2. Select File > New, and add a new
Objective-C class.
Make sure that the Subclass dropdown is set to
UITableViewCell
, and save it as MyCustomCell.m. Make sure that “Also create ‘MyCustomCell.h’” is selected
M
.
3. Open MyCustomCell.h, and create a property ( Code Listing 5.18). This will be the view that holds your custom control.
4. Switch to MyCustomCell.m, and add the following to the
initWithStyle:reuse
Identifier:
method:
self.selectionStyle = UITableView
CellSelectionStyleNone;
This disables selection of the entire cell; you don’t want the cell to be selected because you will be manipulating your control instead.
5. Implement the
setView:
method:
if (view)
[view removeFromSuperview]; view = aView;
[self.view retain];
[self.contentView addSubview:aView];
[self layoutSubviews];
This adds a view (from the view property) to the cell’s
contentView
and then tells the cell to draw its subviews.
M
Adding a custom cell class to hold your table view details
Code Listing 5.18 The header file for the custom cell class.
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6. Implement the
layoutSubviews
method:
float xOffset = 10.0;
[super layoutSubviews];
CGRect contentRect =
[self.contentView bounds];
CGRect viewFrame = CGRectMake
(contentRect.size.width -
self.view.bounds.size.width -
xOffset,round((contentRect.size.
height - self.view.bounds.size.
height) / 2.0),self.view.bounds.
size.width,self.view.bounds.size.
height); view.frame = viewFrame;
Here you add the view (defined in the view property) to the right side of the cell’s
contentView
.
Code Listing 5.19
shows the complete code for your custom cell class.
7. Open RootViewController.h, and import the header file for your custom cell.
8. Create instance variables to hold two controls for your custom cells and an array to hold the table view content
(
Code Listing 5.20).
continues on page 227 ptg
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Code Listing 5.19 The completed custom cell class.
Code Listing 5.20 The header file for the main table view controller class of the custom cell example.
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9. Switch to RootViewController.m, uncomment the
viewDidLoad
method, and add the following code:
mySwitch = [[UISwitch alloc]
initWithFrame:CGRectZero];
[mySwitch addTarget:self action:
@selector(switchAction:)
forControlEvents:UIControlEvent
ValueChanged];
[mySwitch setOn:YES]; myButton = [UIButton
buttonWithType:
UIButtonTypeRoundedRect];
[myButton setFrame:CGRectMake
(0,0,80,30)];
[myButton addTarget:self action:
@selector(buttonAction:)
forControlEvents:UIControlEvent
TouchUpInside];
[myButton setTitle:@"Tap Me!"
forState:UIControlStateNormal]; arrCells = [[NSArray alloc]
initWithObjects:@"Item 1",
@"Item 2",@"Item 3",nil];
Here you create a switch and a button that you are going to be adding to your custom cells. Notice how you define the target-action methods for both of them within this class also. In this example, you just log the actions to the console.
You also create an array to hold the text for the table view just as you did in previous exercises.
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10. Implement the
tableView:number
OfRowsInSection:
method to return the size of your array, and implement the
tableView:cellForRowAtIndexPath:
method:
UITableViewCell *cell = nil; static NSString
*CellIdentifier = @"Cell"; static NSString *ViewCell
Identifier = @"ViewCell"; switch (indexPath.row) { case 0: cell = [tableView dequeue
ReusableCellWithIdentifier:
ViewCellIdentifier]; if (cell == nil) cell = [[[MyCustomCell
alloc] initWithStyle:
UITableViewCellStyle
Default reuseIdentifier:
ViewCellIdentifier]
autorelease]; cell.textLabel.text =
[arrCells objectAtIndex:
indexPath.row];
((MyCustomCell *)cell).view =
mySwitch; break; case 1: cell = [tableView dequeue
ReusableCellWithIdentifier:
ViewCellIdentifier]; if (cell == nil)
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break; default: cell = [tableView dequeue
ReusableCellWithIdentifier:
CellIdentifier]; if (cell == nil) cell = [[[UITableViewCell
alloc] initWithStyle:
UITableViewCellStyle
Default reuseIdentifier:
CellIdentifier]
autorelease]; cell.textLabel.text =
[arrCells objectAtIndex:
indexPath.row]; break;
} cell = [[[MyCustomCell
alloc] initWithStyle:
UITableViewCellStyle
Default reuseIdentifier:
ViewCellIdentifier]
autorelease]; cell.textLabel.text =
[arrCells objectAtIndex:
indexPath.row];
((MyCustomCell *)cell).view =
myButton; return cell;
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Since you are using custom cells, you need to determine which row is being requested via
indexPath.row
. For the first two rows, you create a custom cell. Notice how you set the view of the custom cell to the switch or the button.
For other rows (the
default
case), the code is the same as in the previous exercise “To create an application with a table view.”
11. Build and run the application.
The completed application displays two custom cells
N
. Selecting the switch or tapping the button will log a message to the console.
Code Listing 5.21 shows the completed code.
This is obviously a simple example, adding only a single view to the cell, but you should be able to see how you could extend it to add multiple controls to your own custom cells. For more information on working with table views, see the Table View Programming Guide for iPhone OS in the developer documentation.
N
The completed custom cell application.
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Code Listing 5.21 The completed code for the custom cell example.
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Code Listing 5.21 continued
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files and
Networking
The iPhone runs a slimmed-down version of the Mac OS X operating system, so the file system is similar to its desktop cousin.
However, iPhone applications run within a security sandbox, a unique area on the iPhone reserved for an application where it can run without affecting the system or any other iPhone applications. So, the files and directories you can actually read and write are somewhat limited. Of course, this also means that other applications can’t gain access to your application’s files!
The iPhone also has some fairly extensive networking capabilities by way of its Wi-Fi,
Bluetooth, and 3G connectivity options. In this chapter, you’ll learn the classes, methods, and functions used to perform many of the common file and networking tasks encountered as an iPhone developer.
In This Chapter
Files
Networking
234
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Files
As you learned in Chapter 1, “Objective-C and Cocoa,” several Cocoa classes have methods to automatically deal with reading and writing files ( Code Listing 6.1). Some of these classes are as follows: n
UIImage
—The
imageNamed:
method will automatically try to load an image from the resources directory of your application bundle.
n n n
NSString
—The
stringWithContentsOf
File:
and
writeToFile:
methods let you load and save strings as files.
Additionally,
NSString
has some other commonly used methods for dealing with file paths.
NSDictionary
and
NSArray
—The
dictionaryWithContentsOfFile:
,
arrayWithContentsOfFile:
, and
writeToFile:
methods allow you to load and save dictionaries and arrays of objects. Note that the objects in your dictionary or array must be property list objects (
NSNumber
,
NSString
,
NSData
,
NSArray
, or
NSDictionary
).
NSData
—This is normally used when dealing with binary files.
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Code Listing 6.1 Many common classes have methods to load and save files.
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The file system
NSFileManager
wraps many of the common actions you will need to perform when dealing with the iPhone file system including creating, deleting, moving, and copying files. You can also use it for getting directory listings, reading and writing file attributes, and more.
n
For example, to copy a file from one location to another, you could write this:
NSFileManager *fm = [NSFileManager
defaultManager];
n
NSError *error;
BOOL ok = [fm copyItemAtPath:
@"somePath" toPath:
@"someOtherPath" error:&error]; if (! ok)
NSLog(@" %@",error.localized
Description);
To get an array of filenames for a path, you can use this:
NSFileManager *fm = [NSFileManager
defaultManager];
NSArray *fileContents =
[fm directoryContentsAtPath:@"/"];
You can read more in the
NSFileManager
class reference of the developer documentation.
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A
The contents of the home directory.
Common directories
The iPhone is quite locked down in regard to which directories you can read and write to, and in practice, you will normally be working with only a couple of directories.
You can retrieve the path of your application by using the
NSHomeDirectory()
function:
NSString *homeDir =
NSHomeDirectory();
If you log the contents of this directory to the console, you’ll notice three directories in addition to your application bundle
A
: n
tmp—This is the temporary directory, which can also be retrieved using the
NSTemporaryDirectory()
function:
NSString *tempDir =
NSTemporaryDirectory();
n
You can use this directory for reading and writing any temporary files you may need in your application. Files in this directory are not guaranteed to continue to exist once you exit your application (they are automatically cleaned out periodically by the system) and are not copied to your computer when you sync your iPhone with iTunes.
Documents—This directory is the designated area for your application to read and write files to. Any files written here are copied to your computer when you sync with iTunes. You can retrieve the documents directory by using the following code:
NSArray *paths = NSSearchPathFor
DirectoriesInDomains(NSDocument
Directory, NSUserDomainMask,
YES);
NSString *docDir = [paths
objectAtIndex:0];
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n
Library—This directory contains cache and preference files used by
NSUserDefaults
. Although you can read and write to this directory, you will not normally need to do so.
You can also read files contained within your application bundle, such as images, movies, sounds, or other files that you have added to your project. These will generally be copied into the resources directory of the bundle. For example, to get the path of an image named apple.png, you can write the following:
NSString *resourcesDir =
[[NSBundle mainBundle]
resourcePath];
NSString *imageDir =
[resourcesDir
stringByAppendingPathComponent:
@"apple.png"];
Although both your application bundle and the home directory can be written to in the iPhone Simulator, they cannot be written to on an actual iPhone. For this reason, you should use the tmp or documents directory if you need to save any files.
Setting the key to YES
UIFileSharingEnabled
in your applications info.plist will enable file sharing so that users can get access to the contents of the documents directory of your application through iTunes
B
. This is an extremely handy way of moving files between your computer and your iPhone applications.
B
Once enabled, file sharing can be accessed via iTunes.
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C
Creating a property list.
D
Adding a new row to a property list.
Working with files
So far, you’ve seen some of the classes, methods, and functions you can use when managing files on the iPhone. Now you’ll look at an example where being able to load and save an
NSDictionary
as a file may come in handy. You’ll create an application (a simple username and password screen) that populates its user interface from an external settings file. Any changes the user makes to the interface will be saved to the settings file so that they can be restored the next time the application is launched.
One way to do this is to ship your application with a default settings file. When the application launches for the first time, you copy these default settings to the documents directory. It is this copy you then use in your application for loading and saving the user’s settings. Since the documents directory is copied to the user’s computer each time they sync with iTunes, you know that any changes the user has made will remain safe.
To create an application to load settings from an external file:
1. Create a new view-based application, saving it as SettingsExample.
2. Choose File > New. In the New File dialog box, select the Other category, select Property List, and click Next
C
.
3. Name the file settings.plist, and click
Finish.
4. Select the settings.plist file in the
Groups & Files pane to show the file in the property list editor view.
5. Right-click the Root key, and select Add
Row
D
.
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6. Change the key from New Item to username, and leave the type as String.
7. Repeat steps 5–6, adding a second item called password. If you want, you can enter a default value for both keys
E
.
8. Open the FilesExampleViewController.h file, and create the instance variables you’ll use to hold the settings dictionary, filename, and user interface elements
(
Code Listing 6.2).
9. Switch to FilesExampleViewController.m, and create the method
getSettings
Dictionary:
, which will be used to read the settings from the file:
NSArray *paths = NSSearchPathFor
DirectoriesInDomains(NSDocument
Directory, NSUserDomainMask,
YES);
NSString *documentsDir = [paths
objectAtIndex:0];
NSString *filePath =
[documentsDir
stringByAppendingPathComponent:
settingsFileName];
NSFileManager *fm =
[NSFileManager defaultManager];
BOOL exists =
[fm fileExistsAtPath: filePath];
You first get the user’s documents directory and use it to construct the filename for the settings file.
NSString *resourcesDir =
[[NSBundle mainBundle]
resourcePath];
NSString *sourcePath =
[resourcesDir
stringByAppendingPathComponent:
fileName];
[fm copyItemAtPath:sourcePath
toPath:filePath error:NULL];
E
The completed property list.
Code Listing 6.2 The header file for the Settings example.
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You next check whether the file exists, and if it doesn’t, you copy the default settings file (created in step 4) from the application bundle into the documents directory.
return [NSDictionary
dictionaryWith
ContentsOfFile:filePath];
You then create a dictionary from this file and return it from the method.
10. Create the
createUI
method used to build the user interface.
There is nothing unusual here: You are adding two
UILabel
s, two
UITextField
s, and a button to the main view. The text values for the username and password fields are retrieved from the
dictSettings
dictionary.
11. Uncomment and implement the
viewDidLoad
method:
settingsFileName =
[[NSString alloc] initWithString:
@"settings.plist"]; dictSettings =
[[NSMutableDictionary alloc]
initWithDictionary:[self
settingsDictionary]];
[self createUI];
Here you set the settings filename and retrieve and initialize a dictionary from the file in the documents directory
(which will be automatically created if necessary). Then you store the dictionary in an instance variable before creating the user interface.
12. The final step is to implement the
saveClick:
method that is called when the user taps the Save button: continues on next page
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NSArray *paths = NSSearchPathFor
DirectoriesInDomains(NSDocument
Directory, NSUserDomainMask,
YES);
NSString *documentsDir = [paths
objectAtIndex:0];
NSString *filePath = [documents
Dir stringByAppendingPath
Component:settingsFileName];
[dictSettings
setValue:txtUserName.
text forKey:@"username"];
[dictSettings setValue:txtPassword.
text forKey:@"password"];
[dictSettings writeToFile:filePath
atomically:NO];
This is almost the reverse of the
getSettingsDictionary:
method.
You set the username and password keys of the settings dictionary to the text field values and then write it to the documents directory.
Code Listing 6.3
shows the completed code.
In this example, you saved not only the username but also the user’s password in the settings file. In a real-world application, you would normally store sensitive information such as passwords in a secure database called the keychain. For more information, refer to the Keychain Services Programming
Guide in the developer documentation.
Code Listing 6.3 The completed code.
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Code Listing 6.3 continued
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Previewing documents
Just like on the Macintosh, the iPhone SDK contains a technology known as Quick
Look for previewing documents. By using a
CLPreviewController
object, you can easily view multiple documents of several formats, including Microsoft Office, Apple iWork, PDF, rich text, images, and more.
Next you’ll see how, with just a couple of lines of code, you can create a simple PDF viewer, complete with paging and touchenabled resizing. This example can, of course, be extended to work with any of the document types supported by Quick Look.
In this example, you’ll view the iPhone
Users Guide, which can be downloaded from Apple at http://manuals.info.apple. com/en/iphone_user_guide.pdf
.
To create a PDF viewer:
1. Create a new view-based application, saving it as QuickLookExample.
2. Drag the iPhone Users Guide PDF into the Resources section in the Groups &
Files pane. Make sure that the “copy items into destination group’s folder (if needed)” check box is selected
F
.
3. In the Groups & Files pane, expand the
Targets section, right-click your application target, and select Get Info.
4. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add the
QuickLook.framework
G
.
F
Copying the PDF into the project.
G
Adding the Quick Look framework.
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Code Listing 6.4 The header file for the PDF viewer.
5. Open QuickLookExampleViewController.h, include the QuickLook.h header, add the protocol
QLPreviewControllerDataSource
, and create an instance variable to hold your Quick Look view controller (
Code
Listing 6.4).
6. Next, switch to QuickLookExample
ViewController.m, uncomment the
viewDidLoad
method, and add the following code:
qlViewController =
[[QLPreviewController alloc]
init]; qlViewController.dataSource =
self;
[self createUI];
Here you are simply creating a Quick
Look preview controller and setting its data source. You also call the
createUI
method, which adds the button that will be used to show the Quick Look preview controller.
7. Next, create the
showPreview
method:
[self presentModalViewController:
qlViewController animated:YES];
which simply shows the Quick Look preview controller on the screen.
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8. Now you need to implement the two
QLPreviewControllerDataSource
data source methods so that the Quick
Look preview controller knows what to display. First you implement the
numberOfPreviewItemsInPreview
Controller:
method. In this example, since we have only a single PDF file, you simply return the number 1.
return 1;
You then implement the
preview
Controller:previewItemAtIndex:
method:
NSString *documentLocation =
[[NSBundle mainBundle]
pathForResource:@"iphone_user_
guide" ofType:@"pdf"];
NSURL *myQLDocument = [NSURL file
URLWithPath:documentLocation]; return myQLDocument;
Here you retrieve the path of your PDF and use it to create and return an
NSURL
object.
Code Listing 6.5 shows the completed code.
9. Build and run the application.
Tapping the Show Preview button causes the Quick Look preview controller to load. You can navigate through the pages of the PDF by flicking your finger up and down on the screen. Note how your current page is displayed in the top-right corner and the document name is displayed in the title bar
H
. By pinching or double-tapping the screen, you should be able to zoom in to read the document in greater detail.
For more information on Quick Look, refer to the Quick Look Framework Reference in the developer documentation.
H
The PDF Viewer application.
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Code Listing 6.5 The completed PDF viewer code.
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Networking
Now you’ll learn how you can accomplish some of the more common networkingrelated tasks on the iPhone. You’ll see how to retrieve content from and send content to web pages. You’ll also see how easy it is to work with web pages that require authentication. Finally, you’ll use the Game Kit API to create a simple peerto-peer chat application.
Retrieving content from web pages
The easiest way to get the HTML contents of a web page is by using the
stringWith
ContentsOfURL:
method of
NSString
. Next you’ll take a look at using this method to retrieve some stock quote data from the
Yahoo! finance web page and display it in your application
A
.
To retrieve stock quotes from a web page:
1. Create a new view-based application, saving it as GetWebContent.
2. Open GetWebContentViewController.h, and add an instance variable to display the web page you will be retrieving:
UITextView *resultsView;
A
Retrieving and displaying stock quotes in an application.
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3. Switch to GetWebContentView
Controller.m, uncomment the
viewDidLoad
method, and add the following code:
CGRect resultsFrame = CGRectMake
(10,10,300,100); resultsView = [[UITextView alloc]
initWithFrame:resultsFrame]; resultsView.font = [UIFont
systemFontOfSize:14.0];
[self.view addSubview:resultsView];
You first create a
UITextView
control that you’ll use to display the stock quote information.
NSString *symbol = @"AAPL,GOOG,
MSFT,YHOO,PALM";
NSString *urlString = [NSString
stringWithFormat:
@"http://finance.yahoo.com/d/
quotes.csv?f=no&s=%@", symbol];
You next create a string containing the
URL of the Yahoo! finance page. Note how
stringWithFormat:
is used to append the list of stock symbols to the query string.
NSURL *url = [NSURL
URLWithString:urlString];
NSString *quotes = [NSString
stringWithContentsOfURL:url
encoding:NSUTF8StringEncoding
error:nil]; resultsView.text = quotes;
Finally, you create an
NSURL
object and use it to populate a string with the contents of the web page before displaying it in your text view.
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Code Listing 6.6 shows the completed code. Notice that there are
NSLog()
statements at the beginning and end of the method. If you examine the console, you will see that the web page content actually takes some time to be downloaded
(depending on your Internet connection speed, of course). You may also have noticed that your application was unresponsive while the download was taking place.
This is because
stringWithContentsOfURL:
uses a synchronous connection, so your application will effectively pause until the download is completed. Worse still, if the page cannot be loaded (either as a result of a bad URL or the server not responding), you won’t be told of any errors. You can check this for yourself by changing the URL to an invalid page.
Code Listing 6.6 Retrieving stock quotes from a web page.
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Apple provides a more robust way of retrieving web pages—the
NSURLConnection
class—which allows you to use an asynchronous connection as well as deal with situations such as timeouts, server redirects, and errors.
To update the application to use an asynchronous connection:
1. Open GetWebContentViewController.h, and add an instance variable to hold the web page data:
NSMutableData *receivedData;
2. Switch to
GetWebContentViewController.m, and modify the
viewDidLoad
method, replacing the call to
stringWithContentOfURL
:
receivedData=[[NSMutableData
alloc] initWithData:nil];
NSURLRequest *req=[[NSURLRequest
alloc] initWithURL:url];
NSURLConnection *conn =
[[NSURLConnection alloc]
initWithRequest:req
delegate:self];
Here you first initialize an instance variable to hold the web page contents as it’s received. Next you create an
NSURLRequest
object, assigning it the same
NSURL
you used last time, and then you use this
NSURLRequest
object to create an
NSURLConnection
object.
NSURLConnection
asynchronously loads the web page and sends messages to its delegate at various points during the process.
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3. Finally, you need to implement the following three delegate methods of
NSURLConnection
:
The
connection:didReceiveData:
delegate method will be called whenever some data is received from the
NSURLConnection
. Here you simply append the data to any that has already been received.
The
connection:didFailWithError:
delegate method will be called if an error occurs. In this example, you display the error, but in a larger application, you might want to clean up your
receivedData
object.
The
connectionDidFinishLoading:
delegate method is called when the
NRURLConnection
has finished loading the web page. You then create a string for the
receivedData
object and display it in the text view as before.
Code Listing 6.7 shows the updated application. If you again put
NSLog()
statements at the beginning and end of the
viewDidLoad
method, you should notice that the time stamp difference is almost zero and that your application starts up and displays the text view even before the stock data has finished downloading. If you also change the URL to an invalid web page, you should now see the error being handled and displayed in an alert view.
Apple recommends that any application that requires an Internet connection should first test for availability of the connection and inform the user if one isn’t available.
Although the code to perform this check is beyond the scope of this book, Apple provides a sample application (the “Reachability” example) that shows how this can be done. You can download it from the
“Coding How-Tos” section of the iPhone
Developer Connection Web site.
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Code Listing 6.7 The code, updated to retrieve stock quotes asynchronously.
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Parsing XMl
In the previous example, the stock quotes were returned as a comma-separated list.
It’s much more common, however, to have to deal with XML data when communicating with Web services or Internet-related data.
For both retrieving and parsing XML data, you can use the
NSXMLParser
class. Once an
NSXMLParser
object is initialized with a source of XML data, you simply call its parse method to process the data. Delegates of this class are notified as the XML is processed, and you can capture details about each XML element or attribute as the
XML is parsed by implementing the corresponding delegate methods.
Next you’ll look at a simple example of how you might go about using an
NXSMLParser
object to retrieve information from an RSS feed (in this case, the daily news feed from the CNN Web site), adding each parsed
RSS record to an array. This example has only basic error handling, and the resulting array is simply logged to the console after the XML has been parsed. In a real-world example, you would likely save this data or display it in your application.
Each XML record of the RSS feed is in the following format:
<item>
<title>Article Title</title>
<guid>Article URL</guid>
<pubDate>publication
Date</pubDate>
</item>
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Code Listing 6.8 The header file for the RSS reader.
To build an application to parse an RSS feed:
1. Create a new view-based application, saving it as XMLExample.
2. Open XMLExampleViewController.h, add the
NSXMLParserDelegate
protocol, and create some instance variables
( Code Listing 6.8):
NSXMLParser *parser;
NSMutableArray *articles;
NSString *currentElement;
NSMutableString *currentTitle;
NSMutableString *currentGuid;
NSMutableString *pubDate;
BOOL itemActive;
The
parser
variable is your XML parser object. The
articles
array will hold your parsed data, and the rest of the variables are used during parsing of the
XML data.
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3. Switch to XMLExampleViewController.m, uncomment
viewDidLoad
, and add the following code:
articles = [[NSMutableArray alloc]
init];
You first create the array you will use to hold your parsed data. The array is defined as mutable since you don’t know how much data you will be parsing.
NSURL *url = [NSURL URLWithString:
@"http://rss.cnn.com/rss/edition.
rss"]; parser = [[NSXMLParser alloc]
initWithContentsOfURL:url]; parser.delegate = self;
[self createUI];
You then create your
NSXMLParser
object, initialize it with the URL of the
RSS feed, and set the delegate of the parser. Finally, you call a method to create the UI of the application. As with the earlier examples, this simply consists of a button to begin parsing the XML.
4. Next you implement the parser delegate methods:
parserDidStartDocument:
is called when the parser begins parsing.
[articles removeAllObjects];
Here you make sure the articles array is empty.
parser:validationErrorOccurred:
and
parser:parseErrorOccurred:
will be called if the XML data is invalid or cannot be parsed at all. In this example, you show an alert dialog if either error occurs.
parser:didStartElement:namespaceURI: qualifiedName:attributes:
will be
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called each time a new XML element is parsed.
currentElement = elementName; if ([elementName isEqualToString:
@"item"])
{
itemActive = YES;
currentTitle = [[NSMutableString
alloc] init]; currentGuid = [[NSMutableString
alloc] init]; pubDate = [[NSMutableString alloc]
init];
}
You first store the element name in an instance variable (to be used later) and then check to see whether the element is called
item
(indicating the start of a new RSS record). If yes, you initialize some variables that you will use to store the RSS record data. You also set a flag—
itemActive
—to indicate that an RSS record has started parsing.
This flag allows you to ignore any XML data that may be parsed outside of an
<item>..</item>
block.
parser:foundCharacters:
is called as the XML data is parsed:
if (itemActive)
{
NSString *fixedString = [string
stringByTrimmingCharactersInSet:
[NSCharacterSet whitespaceAnd
NewlineCharacterSet]]; if ([currentElement
isEqualToString:@"title"])
[currentTitle appendString:
fixedString];
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5. After checking that you are currently parsing an RSS record (using the
itemActive
variable created earlier), you check the current element and append the incoming string to the relevant instance variable. Note how the string is first trimmed of any invalid whitespace and newline characters first.
6. Next you implement
parser: didEndElement:namespaceURI: qualifiedName:
, which is called when parsing reaches the end of an XML element:
if ([elementName isEqualToString:
@"item"])
{
NSDictionary *record =
[NSDictionary dictionaryWith
ObjectsAndKeys:
currentTitle,@"articleTitle",
currentGuid,@"articleURL",
pubDate,@"publicationDate", nil];
[articles addObject:record];
Here again you check to see whether you’ve reached the end of the RSS record (indicated by an element named
item
), and if so, you create a dictionary of the parsed RSS record and add it to your articles array.
7. Finally, you implement
parserDid
EndDocument:
, which is called when the parser finishes parsing the XML data:
NSLog(@"%@",articles);
Here you just log the contents of the
articles
array to the console.
Code Listing 6.9 shows the completed code. continues on page 261
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Code Listing 6.9 Retrieving XML data from an RSS feed.
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Code Listing 6.9 continued
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8. Build and run your application. Tapping the Retrieve XML button will parse the
RSS feed, and the resulting array will be logged to the console
B
.
B
Logging the contents of the articles array to the console.
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Sending data to Web pages
So far, you’ve seen how to retrieve data
(an HTTP “GET”) from a Web page, using the query string to pass information to the page. You may, however, want to write an application that simulates the user completing and submitting a form on a Web page (usually done with an HTTP “POST”).
In this example, you’ll create an application that submits a search form to Wikipedia and displays the results in a Web view
C
.
Note that Wikipedia could also be searched by passing the search criteria on the query string, a technique you’ve already learned in the “To retrieve stock quotes” exercise earlier in this chapter, so this example is for illustrative purposes only.
To create an application to search Wikipedia:
1. Create a new view-based application, saving it as PostWebContent.
2. Open PostWebContentController.h, and create some instance variables
( Code Listing 6.10):
NSMutableData *receivedData;
UIWebView *resultsView;
NSString *baseURL;
Again, the
receivedData
variable will hold the web content,
resultsView
will be used to display the resulting HTML, and finally
baseURL
will be used to correctly resolve any links in the HTML.
C
Searching Wikipedia and displaying the results.
Code Listing 6.10 The header file for the
Wikipedia search application.
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3. Switch to PostWebContentController.m, uncomment the
viewDidLoad
method, and add the following code:
CGRect resultsFrame = CGRectMake
(10,10,300,440); resultsView = [[UIWebView alloc]
initWithFrame:resultsFrame];
[self.view addSubview:resultsView];
You first create a web view and add it to your main view. The web view will display the search results.
baseURL = @"http://en.wikipedia.
org";
NSString *urlString = [baseURL
stringByAppendingString:@"/w/
index.php"];
NSURL *url = [NSURL URL
WithString:urlString];
Next construct your URL just as you did before.
receivedData=[[NSMutableData
alloc] initWithData:nil];
NSMutableURLRequest *req=
[[NSMutableURLRequest alloc]
initWithURL:url cachePolicy:
NSURLRequestReloadIgnoringLocal
CacheData timeoutInterval:30.0];
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Now, initialize an instance variable to hold the content as it’s received.
This time, however, you create an
NSMutableRequest
because you will be setting some properties on the request.
You also tell the request to ignore any caching that may be happening and to time out after 30 seconds.
[req setHTTPMethod: @"POST"];
[req setHTTPBody:[@"search=iPhone"
dataUsingEncoding:NSISOLatin1
StringEncoding]];
NSURLConnection *conn =
[[NSURLConnection alloc]
initWithRequest:req
delegate:self];
Finally, you set the method of the request to be a POST, set a key-value pair to match the form file contained on the page, and then create an
NSURLConnection
just as you did earlier.
The delegates are implemented in the same way as earlier—only this time you load the resulting HTML into your web view and display the page. Notice that you also implement a fourth delegate,
connection:didReceiveResponse:
. This method is called each time a new response is received, which allows you to handle any page redirects that might happen. In this example, you reset the
receivedData
variable so that you have only the contents of the final page.
Code Listing 6.11 shows the completed code.
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Code Listing 6.11 Posting content to a web page.
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Responding to HTTP Authentication
So far, you’ve seen how to get data from and send data to web pages. Next you’ll learn how you deal with pages that require authentication by posting a status update to Twitter
D
.
To create an application to update your status on Twitter:
1. Create a new view-based application, saving it as PostTweet.
2. Open PostTweetViewController.h, and create some instance variables
( Code Listing 6.12):
NSMutableData *receivedData;
UITextField *myTextField;
UIButton *myButton;
Just as in previous examples,
received
Data
will hold the response from the
Twitter server when you post your status update.
3. Switch to PostTweetViewController.m, uncomment the
viewDidLoad
method, and add the following code:
[self createUI]; receivedData=[[NSMutableData
alloc] initWithData:nil];
You first call a method to create your user interface (a text field for the status update and a button to send the update) and then create the
receivedData
object.
D
Posting a status update to Twitter.
Code Listing 6.12 The header file for the Twitter application.
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4. Implement the
tweetClick:
method:
[receivedData setLength:0];
NSString *twitterURL = @"http://
twitter.com/statuses/update.xml";
NSURL *url = [NSURL
URLWithString:twitterURL];
NSMutableURLRequest *req=
[[NSMutableURLRequest alloc]
initWithURL:url cachePolicy:NSURL
RequestReloadIgnoringLocal
CacheData timeoutInterval:30.0];
[req setHTTPMethod: @"POST"];
NSString *twitterBody=[NSString
stringWithFormat:@"status=%@",
myTextField.text];
[req setHTTPBody:[twitterBody
dataUsingEncoding:NSISOLatin1
StringEncoding]];
NSURLConnection *conn =
[[NSURLConnection alloc]
initWithRequest:req
delegate:self];
[req release];
[conn release];
This is almost the same code as you saw in the previous exercise. After creating and populating an
NSURL
object with the URL of the Twitter update page, you create a key-value pair containing your text field’s text and post it to the server.
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5. The delegates are implemented just as previously, but this time, since Twitter requires authentication, you also need to implement the
connection:didReceive
AuthenticationChallenge:
delegate:
NSString *userName = @"";
NSString *userPassword = @""; if ([chg previousFailureCount]
== 0)
{
NSURLCredential *newCredential; newCredential=[NSURLCredential
credentialWithUser:userName
password:userPassword
persistence:NSURLCredential
PersistenceNone];
[[chg sender] useCredential:
newCredentialforAuthentication
Challenge:chg];
} else
[[chg sender]
cancelAuthentication
Challenge:chg];
By looking at the
previousFailureCount
, you can see how many times you have attempted to authenticate and have failed. Assuming you have never attempted to authenticate, you create an
NSURLCredential
object
(using your Twitter username and password) and send these using the
useCredential:forAuthentication
Challenge:
method to the connection you created earlier.
Code Listing 6.13
shows the completed code.
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Code Listing 6.13 Posting a status update on Twitter.
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Code Listing 6.13 continued
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In a real-world example, you would likely store your username and password in the device keychain. Likewise, you would probably try to authenticate several times. In the previous exercise, when the
cancelAuthenticationChallenge:
method is called, the
connection: didFailWithError:
delegate can be used to handle the failed authentication.
Using a delegate for authentication works well in situations such as these.
If your
NSURLConnection
request requires authentication, then the delegate method is called—otherwise, it won’t be. You don’t need to worry about constantly checking to see whether the authentication credentials are still valid on each request.
Notice also how in the
connectionDid
FinishLoading:
delegate the
receivedData
object is logged to the console. Although this object was not strictly necessary for the example to work, you can use it to parse the Twitter server response and provide some type of meaningful feedback.
Creating peer-to-peer applications
By using the Game Kit API, you can easily create peer-to-peer applications with very little code. All the networking complexity is handled for you, letting you connect devices over Bluetooth without having to do any pairing.
The
GKSession
class is built on top of the
Bonjour networking service and allows you to create both client/server and peer-topeer connections between devices. In a peer-to-peer scenario, you are notified of the state of the session (such as when a connection is successfully made) via its delegate methods. The
GKSession
class also handles all the sending and receiving of data between peers.
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For selecting which peer to communicate with, you can use the
GKPeerPicker
Controller
class. This presents a standard
UI showing you a list of the other peers
E
. It also allows you to accept or decline a peer-to-peer connection request from another iPhone
F
.
Apple also provides an API to handle voice communication; we won’t cover the API here, but you can implement it without too much code. Sample code for building a peer-to-peer voice chat is available in the
“Coding How-Tos” section of the iPhone
Developer Connection Web site.
Although the Game Kit API is geared toward in-game communication and voice, you can use it for other peer-to-peer applications. In this section, you’ll use the Game Kit API to see how little code is needed to create a simple peer-to-peer chat application.
E
The peer picker controller lets you browse for other peers to communicate with.
F
Using the peer picker controller to accept an incoming chat request.
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G
The peerto-peer chat application.
Unfortunately, in the current version of the iPhone development tools, the simulator cannot communicate with an iPhone over Bluetooth. This leaves the option of using either two iPhones or two computers both running the simulator. In the example presented here, the code is running in the simulator on two computers
G
.
To create a peer-to-peer chat application:
1. Create a new view-based application, saving it as P2PExample.
2. In the Groups & Files pane, expand the
Targets section, right-click your application target, and select Get Info.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add Game-
Kit.framework
H
.
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H
Adding the Game Kit framework.
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4. Open P2PExampleViewController.h, include the GameKit.h header, add the
GKPeerPickerControllerDelegate
and
GKSessionDelegate
protocol declarations, and create some instance variables (
Code Listing 6.14):
GKPeerPickerController *myPicker;
GKSession *mySession;
UITextView *myTextView;
UITextField *myTextField;
You create a peer picker controller that provides an interface to select who to chat with and a session object that will be used to connect and communicate with the other peer. You also create the objects that you’ll use to create your user interface.
5. Switch to P2PExampleViewController.m, uncomment the
viewDidLoad
method, and add the following code:
[self createUI]; myPicker = [[GKPeerPicker
Controller alloc] init]; myPicker.connectionTypesMask =
GKPeerPickerConnectionType
Nearby; myPicker.delegate = self;
[myPicker show];
You first call a method to create the user interface (a text view for the conversation and a text field and button to send messages). Next you create the peer picker. Setting
connectionTypesMask
to
GKPeerPickerConnectionTypeNearby
will make the iPhone use Bluetooth to look for other peers.
Code Listing 6.14 The header file for the peer-topeer chat application.
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I
Selecting a peer from the peer picker controller.
6. Implement the peer picker delegate method,
peerPickerController:session
ForConnectionType:
, which is called when the peer picker is shown:
mySession = [[GKSession alloc]
initWithSessionID:@"p2pTest"
displayName:nil sessionMode:GKSessionModePeer]; mySession.delegate = self; return mySession;
This method creates and returns a new peer-to-peer session, giving it the ID p2pTest. Any other peers with the same session ID will show up in the peer picker
I
.
7. You need to implement a delegate method used by your
GKSession
object.
The
session:didChangeState:
method is called whenever your session changes state (in this example, when you get a connection to another peer):
[mySession setDataReceiveHandler:
self withContext:nil];
[myPicker dismiss];
[self sendChatText:@"connected"];
Here you tell the session to look in the current object for its receive handler.
You also tell the peer picker to hide
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8. Implement the receive handler method
receiveData:fromPeer:inSession: context:
that was set up in the previous step:
NSString *receivedText =
[[NSString alloc] initWithData:
dataencoding:NSUTF8String
Encoding];
NSString *peerName = [[NSString
alloc] initWithString:[session
displayNameForPeer:peer]]; myTextView.text = [NSString
stringWithFormat:@"%@\n[%@]:
@",myTextView.text,peerName,
receivedText];
You create a string from the received data (the text sent from the other peer), get the name of the peer, and then append everything to your text view to show the conversation.
9. Now that you’ve written the receive method, the final step is to implement the send method (called by the Send button):
NSData *sendData = [newText
dataUsingEncoding:NSUTF8
StringEncoding];
[mySession sendDataToAllPeers:
sendData withDataMode:
GKSendDataReliable error:nil]; myTextView.text = [NSString
stringWithFormat:@"%@\n[ME]:
%@",myTextView.text,newText];
This is just the reverse of step 8; here you’re creating an
NSData
object from your message string and sending the data to the other peer. Again, you append this text to the text view to show the conversation.
Code Listing 6.15
shows the completed code.
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Code Listing 6.15 The completed code for the peer-to-peer chat application.
code continues on next page
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Code Listing 6.15 continued
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Touches, Shakes, and orientation
The iPhone’s primary interface is its large
Multi-Touch display. Since it doesn’t have a physical keyboard, everything is accomplished via this screen. The iPhone takes things much further than a simple keyboard, however, allowing you to interact with your applications in a very natural and intuitive way. Objects onscreen can be moved, zoomed in or out, and scrolled using simple gestures.
The iPhone can also respond to changes in orientation; it can automatically switch and resize the display to portrait or landscape when you rotate the phone, and it can react to shakes and tilting.
In this chapter you’ll see how easy it is to add both single-touch and Multi-Touch support to your applications, including responding to tapping, pinching, rotating, and zooming. You’ll learn how you can respond to shake motions before looking at the iPhone’s accelerometer and how to control your application UI based on changes in the phone’s orientation.
In This Chapter
Touch
Multi-Touch Gestures
The iPhone Accelerometer
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292
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Touch
In the iPhone SDK, all
UIKit
classes that descend from
UIView
are what are known as responder objects—subclasses of the
UIResponder
class. Among other things, this class is responsible for providing access to and handling touch and motion events within an iPhone application.
Touch-based events are handled via four main methods: n
touchesBegan:withEvent:
—Sent at the beginning of a touch life cycle, when the user first touches the screen of the iPhone.
n n
touchesMoved:withEvent:
—Sent as the user moves their finger or fingers around on the screen of the iPhone.
touchesEnded:withEvent:
—Sent when the user lifts their fingers off the iPhone screen and ends the touch.
n
touchesCancelled:withEvent:
—
Sent when the system receives a cancellation event. This can occur in situations such as a low-memory warning or when a phone call is received.
Generally, you would use this method to perform any necessary code cleanup for objects and data generated by the other touch methods.
All four of these methods receive a
UIEvent
object containing
UITouch
objects for each finger that is interacting with the screen (or, in the case of the
touchesEnded:withEvent:
method, for each finger that has just been lifted from the screen).
The
UITouch
object allows you to determine not only what is being touched but when and where it was touched. In the case of movement, it also lets you know where the touched object was and where it was moved.
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Code Listing 7.1 The header file of the touchbased application.
To create a touch-based application:
1. Create a new view-based application, saving it as TouchExample.
2. Open the
TouchExampleViewController.h file, and create an instance variable to hold the view you will be controlling by touch
( Code Listing 7.1).
3. Switch to the TouchExampleView
Controller.m file, uncomment the
view DidLoad
method, and add the following code:
float boxSize = 100.0;
CGRect redBoxRect = CGRectMake
(110,180,boxSize,boxSize); redBox = [[UIView alloc]
initWithFrame:redBoxRect]; redBox.backgroundColor =
[UIColor redColor];
[self.view addSubview:redBox];
Here you are simply creating a
UIView
with a red background, setting its dimensions, and adding it to the main.
4. Implement
touchesMoved:withEvent:
to handle the touch movement:
UITouch *touch = [[event touches
ForView:redBox] anyObject];
CGPoint currentPoint = [touch
locationInView:self.view];
You first retrieve the touch events for the red box view, and then you calculate its location (in relation to its containing view).
[touch view].center =
currentPoint;
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Then you set the center of the red box view to the point being touched.
Code Listing 7.2 shows the completed application code.
5. Build and run the application.
You should be able to move the red box by touching the iPhone’s screen.
Code Listing 7.2 The completed touch-based application.
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Code Listing 7.3 The updated header file for the touch-based application.
This simple exercise shows how easy it is to add touch support to applications. Now you’ll extend the example to deal with multiple views onscreen, allowing them to be moved around independently of each other. You’ll also add a simple zoom animation effect to show which view you are currently touching.
To update the touchbased application:
1. Open TouchExampleViewController.h, and create two more instance variables
( Code Listing 7.3).
2. Modify the
viewDidLoad
method to create three different-colored boxes, and add them to the main view.
3. Implement the
touchesBegan:withEvent:
method:
UITouch *touch = [touches
anyObject]; if (touch.view != self.view)
{...
This time, since you have multiple views being touched, you need to check that you are not receiving a touch event from the main, containing view:
[self.view bringSubviewToFront:
touch.view];
You then make sure the view you are touching moves to the front of the screen:
float zoom = -25.0;
CGRect newRect = CGRectInset
([touch.view frame], zoom,zoom);
[UIView beginAnimations:nil
context:NULL];
[UIView setAnimationDuration:0.2];
[touch.view setFrame:newRect];
[UIView commitAnimations];
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Next, you create a
CGRect
that has a frame 25 pixels larger than the touched view and tell the touched view to resize itself. Doing this inside a
beginAnimations...commitAnimations
block makes the resize animate nicely.
4. Finally, you implement the
touchesEnded: withEvent:
method, which is essentially the reverse of the previous step.
Notice that this time you specify a positive value for the
CGRectInset
function, creating a smaller
CGRect
.
Code List-
ing 7.4 shows the updated code.
Code Listing 7.4 The updated touch-based application.
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A
Moving multiple views by touch.
Code Listing 7.4 continued
5. Build and run your application.
Touching a colored box should cause it to come to the front and animate to a larger size
A
. You can move the box around the screen, and when you let go, it will animate back down to its original size.
Adding tapping support
The
tapCount
property of a
touch
object is the key to adding tap and long-touch support to your applications.
If you revisit the
touchesBegan:withEvent:
method of the previous example and add the following line:
NSLog(@"tap count: %i",[touch
tapCount]);
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you can see the tap counts being logged to the console
B
. There’s a problem here, however: Along with double-tap events, you still see events for the single-tap. You need to figure out a way of telling these two apart and ignoring the single-tap events when you double-tap.
One simple way to do this is to add a small delay to when you actually deal with the tap events, canceling earlier tap events when later tap events occur. This sounds confusing, but it’s actually very easy to do.
B
Logging tap counts to the Debugger Console.
Other uses for CGRect
In the previous exercise “To update the touch-based application,” you use CGRectInset to increase or decrease the size of the CGRect. There are many other useful functions that make working with
CGRect
s easier; among them are the following:
CGRectOffset
creates a rectangle with the origin offset to a source CGRect:
float offset = 25.0;
CGRect r1 = CGRectMake(100,100,100,100);
CGRect r2 = CGRectOffset(r1,offset,offset);
CGRectIntersectsRect
lets you determine whether two rectangles intersect each other:
CGRect r1 = CGRectMake(100,100,100,100);
CGRect r2 = CGRectMake(150,150,100,100); if (CGRectInstersectsRect(r1,r2)
NSLog(@"intersecting");
NSStringFromCGRect
is useful for logging CGRects to the console:
CGRect r1 = CGRectMake(100,100,100,100);
NSLog(@"rect: %@",NSStringFromCGRect(r1));
Likewise, CGRectFromString allows you to create a CGRect from a string:
NSString *r = @"{0,0},{100,100}";
CGRect r1 = CGRectFromString(r);
See the CGGeometry reference entry in the Apple developer documentation for more details.
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Code Listing 7.5 Handling double-taps.
To add single-tap and double-tap support:
1. Open TouchExampleViewController.m, and modify the
touchesBegan:withEvent:
method
( Code Listing 7.5):
float tapDelay = 0.4;
This is the amount of time you wait before processing a tap event, which gives you time to check whether it’s a single-tap or a double-tap:
switch ([touch tapCount])
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2. Next you check to see how many taps you have received:
case 1:
[self performSelector:@selector
(singleTap) withObject:touch.view
afterDelay:tapDelay];
If you’ve received a single tap, you make a delayed call to the
singleTap
method:
case 2:
[NSObject cancelPreviousPerform
RequestsWithTarget:
self selector:@selector
(singleTap) object:touch.view];
[self doubleTap:touch.view];
If you get a double-tap, you first cancel the call to the
singleTap
method before calling
doubleTap
.
Notice how this code could easily be extended to add support for triple or even quadruple taps; however, you may have to increase the value for tapDelay
to give the user time to perform more than a double-click.
Adding long-touch support
One other useful touch-based interaction is the touch-and-hold, or long-touch, effect—as seen on the iPhone home screen when you move applications around or delete them.
Just as in the double-tap example, you make a delayed call to the long-touch method in the
touchesBegan:withEvent:
method; however, this time, since you are effectively dealing with a single-tap only, you cancel the call in the
touchesEnded:withEvent:
method instead.
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C
Adding the QuartzCore framework to the project.
Code Listing 7.6 The updated header file.
D
The simulator showing the animated view.
For bonus points, you’ll now make the view
“wiggle” just like on the iPhone home screen.
To add long-touch support:
1. In the Groups & Files pane, expand the
Targets section, right-click your application target, and select Get Info.
2. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add
QuartzCore.framework
C
.
3. Open the
TouchesExampleViewController.h file, and import the QuartzCore framework
( Code Listing 7.6).
4. Back in
TouchesExampleViewController.m, modify the
touchesBegan:withEvent:
method:
float tapDelay = 1.0f;
[self performSelector:@selector
(startWiggle:) withObject:touch.
view afterDelay:tapDelay];
Here you set the tap delay to be a slightly larger value than earlier
(one second) before calling the
startWiggle:
method, passing the view you want to animate.
5. In the
touchesEnded:withEvent:
method, you make sure to cancel any pending touches, and then you tell the touched view to stop animating.
6. Finally, you implement the
startWiggle:
and
stopWiggle:
methods that cause the view to animate.
Code Listing 7.7 shows the completed code.
7. Build and run the application.
If you long-touch one of the views, it should start animating
D
.
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Code Listing 7.7 The completed touch-based application.
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Code Listing 7.7 continued
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Multi-Touch Gestures
So far you’ve looked at dealing with singletouch events only. However, the real power of the iPhone becomes apparent once you start thinking about Multi-Touch events.
Features such as pinching and zooming can be accomplished only when you use multiple fingers to interact with the display of the iPhone.
You’ll now create an application similar to the previous example, but this time you’ll have it support Multi-Touch events.
To create an application that supports Multi-Touch gestures:
1. Create a new view-based application, and save it as MultiTouchExample.
2. Open the MultiTouchExampleView
Controller.h file, and create an instance variable to hold the
Multi-Touch-compliant view
( Code Listing 7.8).
3. Switch to the MultiTouchExample
ViewController.m file, uncomment the
viewDidLoad
method, and add the following code:
float boxSize = 100.0;
CGRect redBoxRect = CGRectMake
(110,180,boxSize,boxSize); redBox = [[UIView alloc]
initWithFrame:redBoxRect]; redBox.backgroundColor =
[UIColor redColor]; redBox.mutipleTouchEnabled = YES;
[self.view addSubview:redBox];
This is just the same code you used in the touch-based application except that this time you’ve enabled Multi-Touch by setting the
multipleTouchEnabled
property of the view to
YES
.
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4. Next, back in the
touchesBegan: withEvent:
method, you retrieve the set of touches for the red box view:
for (UITouch *touch in [event
touchesForView:redBox])
Then you log the location
CGPoint
of the touch event to the console.
Code
Listing 7.9 show the completed code.
continues on next page
Code Listing 7.8 The header file for the Multi-Touch application.
Code Listing 7.9 Logging multiple touches to the console.
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5. Build and run the application, and try touching the red box view with multiple fingers.
You should see multiple touch events being logged in the console
A
. If you are using the simulator, you can simulate multiple touches by holding down the Option key. The simulator is limited to only two simultaneous touches.
Having multiple touches is what gives the iPhone its pinch, rotate, and zoom gestures. You’ll now update the application to add this functionality.
A
Logging touch locations to the Debugger Console.
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B
Rotating the view.
To add pinch, rotate, and zoom gestures:
1. Open MultiTouchExampleView
Controller.m, and modify
touchesMoved:withEvent: if ([[event touchesForView:redBox]
count] == 1)
{
UITouch *touch = [[[event
touchesForView:redBox]
allObjects] objectAtIndex:0]; redBox.transform = transformWith
Rotation(redBox.transform,
touch,redBox,self.view);
}
If there is only a single-touch, you call a function to rotate the view.
if ([[event touchesForView:redBox]
count] == 2)
{
UITouch *touch1 = [[[event
touchesForView:redBox]
allObjects] objectAtIndex:0];
UITouch *touch2 = [[[event
touchesForView:redBox]
allObjects] objectAtIndex:1]; redBox.transform = transformWith
Scale(redBox.transform, touch1,
touch2);
}
If there are two touches, you call a function to scale the view.
Code Listing 7.10
shows the completed code.
2. Build and run the application.
To rotate the red box, use a single finger. To zoom in and out, use two fingers and a zoom or pinch gesture. Now check out the application after a zoom and rotation have taken place
B
.
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Code Listing 7.10 The updated code for the Multi-Touch application. You can rotate the view by touching with a single finger and scale by touching with two fingers.
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Code Listing 7.10 continued
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The iPhone
Accelerometer
The iPhone’s accelerometer allows it to automatically detect movement of the phone such as tilting or shaking. The iPhone knows when the phone is rotated between portrait mode and landscape mode, and it’s even able to tell whether it is face-up or face-down.
Having access to this information enables you to provide a very rich user experience that can dynamically change. For example, the display can automatically adjust when the phone is rotated, and characters in games can be controlled by simply tilting the phone.
You’ll now learn how you go about using the accelerometer in your own applications.
Detecting shakes
Motion events are similar to the touch events described earlier but are much simpler to deal with. An event is generated only when a motion starts or stops—you can’t track individual motions as you can with touch events.
Handling a shake motion is accomplished via three methods: n
motionBegan:withEvent:
—Called when a motion event begins.
n n
motionEnded:withEvent:
—Called when a motion event ends.
motionCancelled:withEvent:
—Called if the system thinks the motion is not a shake. Shakes are determined to be approximately a second or so in length.
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To create an application that supports shakes:
1. Create a new view-based application, saving it as ShakeExample.
2. Open the
ShakeExampleViewController.m file, uncomment the
viewDidAppear:
method, and add the following code:
[self becomeFirstResponder];
For the view controller to receive motion events, it needs to be the first responder —the object at the start of the chain of
UIResponder
subclasses.
You also need to implement one more method to make the view controller the first responder:
- (BOOL)canBecomeFirstResponder { return YES;
}
3. Implement the three methods responsible for handling motion events.
Code
Listing 7.11 shows the completed code.
4. Build and run the application.
If you shake your iPhone, you should see messages being logged to the console. If you are running the application in the simulator, you can generate a shake by pressing Shift+Command+Z.
Determining orientation
To determine which way the iPhone is facing, you use the
UIDevice
singleton and its
orientation
property. If you register for the
UIDeviceOrientationDidChange
Notification
notification, you are told not only when the phone is rotated between portrait and landscape modes but also when it’s face-up or face-down.
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Code Listing 7.11 The completed code for the shake application.
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You’ll now look at some code to detect a change in orientation. In this simple example, you’ll change the background color when the phone orientation changes.
To create an application that detects orientation:
1. Create a new view-based application, and save it as OrientationExample.
2. Open OrientationExampleView
Controller.m, and uncomment the
viewDidLoad
method. Add the following code:
[[NSNotificationCenter
defaultCenter] addObserver:
self selector:@selector
(noteOrientationChanged:) name:
UIDeviceOrientationDidChange
Notification object:nil];
[[UIDevice currentDevice]
beginGeneratingDevice
OrientationNotifications];
You first add yourself as an observer to the
UIDeviceOrientationDidChange
Notification
notification, which is sent every time the orientation changes. You then tell the iPhone to start generating notifications for orientation changes.
3. Finally, you need to write the code to change the background whenever you receive notification of an orientation change.
Code Listing 7.12 shows the completed code.
4. Build and run the application.
Try rotating your iPhone to see the background change color. If you are running the code in the simulator, you can rotate by pressing Command+left arrow or Command+right arrow.
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Code Listing 7.12 Changing the background color in response to a change in orientation.
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Redrawing the interface when the orientation changes
When a user rotates their iPhone between landscape and portrait modes, you are likely to want the application interface to redraw itself. For example, the user might be browsing the Web, and a wider screen would be a more desirable way to view additional content rather than scrolling from side to side.
One way to accomplish this might be to use the
UIDeviceOrientationDid
ChangeNotification
notification and orientation property of
UIDevice
that you just looked at, manually redrawing the interface each time you detect a change in orientation.
The iPhone SDK offers a much more elegant solution, however: autorotation.
Autorotation is handled in your view controller via the method
shouldAutorotate
ToInferfaceOrientation
. This method returns a Boolean value indicating whether the current orientation should be autorotated.
To force an application to stay in portrait mode (the default), simply return
NO
from this method. If you want to support all orientations, you can simply return
YES
.
Otherwise, you can just inspect the
interfaceOrientation
parameter and determine whether you want to autorotate.
You’ll now update the application to use autorotation. You’ll draw a box in the center of the screen with some text on it that will automatically rotate when you change the iPhone’s orientation. The box will maintain its position in the center of the screen after rotation.
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To update the application to use autorotation:
1. Open OrientationExampleView
Controller.h, and create an instance variable to hold the red box view (
Code
Listing 7.13).
2. Back in OrientationExampleView
Controller.m, remove all of the code to change the background of the screen. You can also remove the call to
beginGenerating DeviceOrientation
Notifications
. Modify your
viewDidLoad
method to create a box that you will be rotating:
float boxSize = 100.0; redTextBox = [[UITextView alloc]
initWithFrame:CGRectMake(110,180,
boxSize,boxSize)]; redTextBox.backgroundColor =
[UIColor redColor]; redTextBox.textColor = [UIColor
whiteColor]; redTextBox.text = @"Hello World"; redTextBox.textAlignment =
UITextAlignmentCenter;
Nothing special is going on here—you are just creating a
UITextView
and setting its size, text, alignment, background, and text color properties.
Code Listing 7.13 The header file of the autorotation application.
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The next step is important, however:
redTextBox.autoresizingMask =
(UIViewAutoresizingFlexible
RightMargin
|
UIViewAutoresizing
FlexibleLeftMargin
|
UIViewAutoresizingFlexible
TopMargin
|
UIViewAutoresizing
FlexibleBottomMargin);
When switching between portrait and landscape modes, you want the red box view to keep its position relative to the new orientation. You accomplish this by setting all of its margins to resize automatically—in effect keeping the view in the center of the screen.
3. Finally, uncomment the
shouldAutorotate
ToInterfaceOrientation:
method to enable autorotation.
Since you want to support all orientations, you simply return
YES
from this method.
Code Listing 7.14 shows the updated code.
4. Build and run the application.
Try changing the iPhone between portrait and landscape modes—the red box view will automatically rotate, remaining in the center of the screen. Try removing or commenting out the code that sets the
autoresizingMask
to see the effect on rotating: Although the red box view will still have the same x and y coordinates, the orientation change also changes the width and height of the screen, resulting in the box no longer being drawn at the center of the screen.
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Code Listing 7.14 The updated autorotation code. The box in the center of the screen will automatically rotate when the iPhone is switched between portrait and landscape modes. ptg
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The iPhone accelerometer can respond to changes on three axes.
Responding to the accelerometer
So far you’ve looked at how to detect and make your interfaces orient themselves automatically when the user changes their phone from portrait mode to landscape mode.
The iPhone’s accelerometer is a lot more powerful than this, however, and is capable of giving you live data for all three dimensions (x, y, and z). This means, for example, you could control onscreen elements simply by tilting the phone in the direction you want.
Accelerometer data is delivered to the applications by the
UIAccelerometer
singleton class and a single delegate method,
accelerometer:didAccelerate:
, which gives you the three axes as
UIAcceleration
objects. Under normal gravity, each of these will have a value between -1 and +1, with 0 being the middle or “flat” point
A
. If you increase gravity’s effect on the iPhone by moving it rapidly
(for instance in a “flicking” motion), then these values will increase.
You’ll now create an application that allows you to control the red box from the earlier examples simply by tilting the phone.
Code Listing 7.15 The header file for the tilt application.
To create a tilt-sensitive application:
1. Create a new view-based application, and save it as TiltingExample.
2. Open TiltingExampleViewController.h, add the
UIAccelerometerDelegate
protocol declaration, and create an instance variable to hold the tiltcontrolled view ( Code Listing 7.15).
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3. Back in TiltingExampleViewController.m, uncomment the
viewDidLoad
method, and set up the accelerometer:
[[UIAccelerometer shared
Accelerometer]
setDelegate:self];
[[UIAccelerometer shared
Accelerometer] setUpdateInterval:
(1/40.0)];
This code tells the accelerometer to deliver events to you every 1/40th of a second.
You then create a red box view and add it to the main view, as in the earlier examples.
4. Next, you need to create a method,
moveBoxWithX:andY:
, to move the red box around on the screen. First add this code:
CGPoint boxCenter = redBox.center; boxCenter.x += xAmount; boxCenter.y += yAmount; if (boxCenter.x < 50.0) boxCenter.x = 50.0; if (boxCenter.x > 270.0) boxCenter.x = 270.0; if (boxCenter.y < 50.0) boxCenter.y = 50.0; if (boxCenter.y > 410.0) boxCenter.y = 410.0; redBox.center = boxCenter;
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You may notice the red box is difficult to keep completely still. You’ve really created only a very simple example of how to deal with accelerometer data. In reality, you would normally want to implement some type of filter
(often called a low-pass or high-pass filter) to
“smooth out” the accelerometer data. Apple provides sample code on the Apple Developer
Connection Web site (http://developer.apple
.com) demonstrating this functionality.
This method gets the current center point
(a
CGPoint
) of the red box view and increments its x and y values. After a couple of checks to make sure you haven’t moved the box view offscreen, you tell the view to move to the new location.
5. The final step is to implement the
UIAccelerometer
delegate method
accelerometer:didAccelerate:
, as shown here:
float sensitivity = 25.0f; float xDistance = acceleration.x *
sensitivity; float yDistance = acceleration.y *
-sensitivity;
[self moveBoxWithX:xDistance
andY:yDistance];
You first set up a variable that will control how far you move by tilting; increasing this value will make the view move faster and/or further when you tilt. You next take the incoming x and y accelerometer values and calculate how many x and y pixels you should move before telling the red box view to move. A small tilt results in small x and y values and thus a small movement. A large tilt results in larger x and y values and so a larger movement.
Code Listing 7.16
shows the completed code.
6. Build and run the application (you will need to install it on an iPhone to test it).
Hold your iPhone so that it is face-up.
You should be able to control the red box by tilting the phone.
In the previous exercise, note how you negate the y value. This is because the iPhone coordinate system starts with 0 at the top of the screen and the accelerometer at the bottom of the screen.
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Code Listing 7.16 The completed code for the tilt application.
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Location and Mapping
Having an iPhone means that you need never get lost again. With the iPhone’s built-in Global Positioning System (GPS) hardware and some innovative location and mapping software, not only does your iPhone know where you are at any time, but it can also show you.
The iPhone uses a technology known as assisted GPS to work out where you are.
In addition to the built-in GPS receiver, the iPhone uses triangulation information from cellular towers and Wi-Fi hot spots to increase the accuracy of the location data it delivers to your applications.
In this chapter, you’ll first take a look at
Core Location—the framework that lets you quickly and easily find your current location. You’ll then look at the Map Kit framework, which enables you to add maps powered by the popular Google
Maps engine to your own applications.
You’ll see how easy it is to perform reverse geocoding to get the address of a location, too. Finally, you’ll combine all of these ideas into a mapping application that reproduces much of the functionality of the native Maps application.
In This Chapter
About Core Location
About Map Kit
Putting It All Together
312
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About Core location
Core Location is the framework used to add location awareness to your iPhone applications. It’s deceptively simple in its design.
The
CLLocationManager
class and its delegates provide the mechanism by which location information gets delivered to your application. Simply create an instance, optionally set some accuracy properties, and then call the
startUpdatingLocation
method.
CLLocation
events are generated via the delegate methods of your
CLLocation
Manager
instance.
CLLocation
objects encapsulate not only geographical coordinates but also information such as speed, altitude, heading, and accuracy.
To make your application location aware:
1. Create a new view-based application, saving it as
CoreLocationExample
A
.
2, In the Groups & Files pane, expand the
Targets section, right-click your application target, and choose Get Info.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add
CoreLocation.framework
B
.
4. Open the CoreLocationExampleView
Controller.h file, import the
CoreLocation
framework, add the
CLLocationManager
Delegate
protocol declaration, and create an instance variable to hold your location manager ( Code Listing 8.1).
A
Creating a view-based application.
B
Adding the Core Location framework to your project.
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5. Switch to the CoreLocationExample
ViewController.m file, uncomment the
viewDidLoad
method, and add the following code:
lm = [[CLLocationManager alloc]
init]; lm.delegate = self;
[lm startUpdatingLocation];
You create your
CLLocationManager
instance, setting the delegate to be the view controller (
self
) and then telling the location manager to begin sending location events.
Code Listing 8.2 shows the completed application code.
Code Listing 8.1 The header file for the core location application.
Code Listing 8.2 A bare-bones core location application.
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Handling location updates
Believe it or not, that’s it—your application is now location aware. However, you still don’t have any way of dealing with the information the location manager is giving you. For this you must implement the required delegate methods (recall that you added the
CLLocationManagerDelgate
protocol back in the CLLocationManager.h file).
CLLocationManager
has just two delegate methods. The first,
locationManager: didUpdateToLocation:fromLocation:
, is called whenever the location manager updates a new location. Both the previous location and the new location are passed unless this is the first location event, in which case
fromLocation:
will be
nil
.
The second delegate method,
location
Manager:didFailWithError:
, lets you deal with any errors that have occurred with the location manager trying to retrieve a location value. In this situation, you’d normally want to stop your location manager with a call to
stopUpdatingLocation
in order to save battery power.
Code Listing 8.3 shows the updated Core
LocationExampleViewController.m file.
Output is sent to the console, showing latitude/longitude coordinates, accuracy of the result (in this case plus or minus 100m), your speed, your course or direction, and a time stamp of when the location event occurred
C
.
Code Listing 8.3 The core location application updated to log to the console.
C
The Debugger Console displaying location information.
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Notice how, to preserve battery power, you call stopUpdatingLocation on the location manager as soon as you have either a location or an error.
When the location manager is first started (via startUpdatingLocation ), it will normally generate a number of location updates in quick succession. These are generally baseline or cached locations that are often inaccurate and can be ignored. You will investigate a technique to handle this situation later in the chapter.
The CoreLocation framework also offers two other methods— startMonitoring
SignificantLocationChanges and stopMonitoringSignificantLocation
Changes —which work in exactly the same way as the method described here but result in fewer location updates being generated. These methods use significantly less power, so Apple recommends using them when your application does not need to be updated frequently.
Testing outside the simulator
If you are navigationally savvy, you may have noticed that when you run the previous example for yourself, the latitude and longitude do not correspond to your own location (that is, unless you are currently working for Apple). When Core Location– based code is run in the iPhone Simulator, it will always report a location of “1 Infinite
Loop, Cupertino” (Apple’s headquarters).
Obviously, this makes testing elements such as course and speed impossible in the simulator. Additionally, if you were walking around with your iPhone testing your application, you wouldn’t be able to view console output on your computer screen.
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From now on, you’ll assume the examples in this chapter are running on an actual device rather than in the simulator. You’ll add a
UITextView
to your iPhone’s main view and write some code to log output to it instead of to the console.
You could just have easily hooked up
UILabel
controls or other, more attractive UI elements—this is just a convenient shortcut that allows you to easily display logging information with minimal effort.
To add logging of location data to the iPhone screen:
1. In CoreLocationExampleViewController.h, create an instance variable to hold your view ( Code Listing 8.4):
UITextView *logView;
2. Switch to CoreLocationExampleView
Controller.m, and create the
logToScreen:
method you will use to log text to the iPhone’s screen:
CGPoint pt = logView.
contentOffset;
You first set a variable to hold the
UIView
’s current content position in its scroll view:
logView.text = [NSString
stringWithFormat:@"%@\n%@",
logView.text,output];
Code Listing 8.4 The updated header file.
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D
Logging information is displayed on the iPhone.
Next you append the new text and make sure the view scrolls properly if the new text is too large for a single screen:
[logView setContentOffset:pt
animated:NO];
[logView scrollRangeToVisible:
NSMakeRange([logView.text
length], 0)];
3. Update the
viewDidLoad
method to create and add the new view:
logView = [[UITextView alloc]
initWithFrame:[self.view
bounds]]; logView.editable = NO; logView.userInteractionEnabled =
YES;
[self.view addSubview:logView];
4. Finally, to make things work as closely to
NSLog()
as possible, define the
DCLog
macro at the top of the file:
#define DCLog(format, ...)
[self logToScreen:[NSString
stringWithFormat:format,
## __VA_ARGS__]];
You can now replace calls to
NSLog()
with a call to
DCLog()
. Logging information will be displayed on the iPhone’s screen
D
.
Increasing the accuracy
Up to this point, you may have noticed that the location information you are receiving isn’t particularly accurate. This is because the location manager often returns cached or baseline “best-guess” values when it’s first started, becoming increasingly accurate over time.
You can do a number of things to filter out these unwanted location events and get a more accurate result.
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You’ve used only the
description
property of the
CLLocation
events so far, but you could use a number of other properties: n
altitude
—A positive or negative value depending on whether you are above or below sea level n n n
coordinate
—A
CLLocationCoordinate
type containing latitude and longitude information
course
,
speed
—The direction and speed (in meters) in which the iPhone is traveling
horizontalAccuracy
,
verticalAccuracy
—
How accurate the coordinate and altitude values are
course
is measured in degrees, with due north being 0, east being 90, south being
180, and west being 270. You probably noticed in the first example that both the course and speed values were
–1.0
. Having only a single location means these values can’t be calculated.
A negative value for horizontal
Accuracy or verticalAccuracy generally indicates that the location event can be ignored.
Adding a timeout
You also want to think about saving iPhone power by timing out and turning off the location manager if you don’t receive a valid location within a reasonable amount of time.
To add timeouts to the location manager:
1. In CoreLocationExampleViewController
.h, add a new instance variable to hold your timeout:
NSTimer *timer;
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2. Switch to CoreLocationExampleView
Controller.m, and add the following new code to your
viewDidLoad
method:
lm.desiredAccuracy =
kCLLocationAccuracyBest; lm.distanceFilter =
kCLDistanceFilterNone;
This tells the location manager how accurate it should be and how far (in meters) the user must move laterally before a new location event is generated.
3. Now set your timer to expire after 1 minute:
timer = [NSTimer scheduledTimer
WithTimeInterval:60 target:self
selector:@selector
(locationManagerDidTimeout:
userInfo:) userInfo:nil
repeats:false];
The
desiredAccuracy
code tells the location manager how accurate it should attempt to be when generating location events. Possible values for this property range from “best” to 3km. It’s worth noting, however, that although the location manager will attempt to achieve the defined accuracy, it is not guaranteed.
In this example, you’re using the most accurate settings for both
desired
Accuracy
and
distanceFilter
. It’s important to remember that using these settings may take longer to return a location and will have more of an impact on the iPhone battery life.
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4. Update the location manager delegate to check the age of the location event:
NSTimeInterval eventAge =
[newLocation.timestamp
timeIntervalSinceNow]; if (abs(eventAge) < 5.0)
You are interested only in events that occurred within the last five seconds. This will filter out any cached location data.
If an event is new enough, you next check the accuracy:
if ([newLocation horizontal
Accuracy] > 0.0f && [newLocation
horizontalAccuracy] <= 100.0f)
which will give only those events that are accurate to within 100m of your actual position (making sure to also ignore negative, invalid values).
Lastly, you stop the location manager and timer and output the result.
5. There are still two more things to do.
First you need to handle when a location can’t be found:
(void)locationManagerDidTimeout:
(NSTimer *)aTimer userInfo:(id)
userInfo
This simply stops the location manager and logs an error to your screen.
6. Finally, make sure that the timer is stopped if an error occurs by adding the following to the
locationManager: didFailWithError:
delegate:
[timer invalidate];
Code Listing 8.5 shows the completed code.
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Code Listing 8.5 The completed core location code.
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Code Listing 8.5 continued
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E
The results of a location search.
Now you’ll see the result of a successful location search
E
. Try running this code on your iPhone—you should see the location events as they arrive (you may need to increase the timeout value if you are indoors), increasing in accuracy over time. Try changing the values for
desiredAccuracy
and
distanceFilter
to see how they affect the results of changing or removing the check for cached locations.
Since the location manager works by gradually increasing accuracy and “zeroing in” on a location, it actually may be the case that the first result, although reported as inaccurate, is in fact correct.
There’s always going to be a trade-off between displaying potentially inaccurate information quickly versus making the user wait longer for a more accurate result. The code in the previous example is just one approach. Another idea might be to decrease the desiredAccuracy level and instead adopt a strategy of counting location events, waiting for a number to arrive before accepting one as valid. The method you choose to use will be determined by your application’s requirements.
Accessing the compass
If your iPhone contains a compass, you can receive heading information in much the same way as location updates.
Heading updates are generated by the location manager as
CLHeading
objects, containing attributes for heading values in relation to both magnetic and true north.
These attributes are measured in degrees, with
0
representing north and
180
representing south.
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To check whether the iPhone supports heading updates, you use the
heading
Available
class method of the location manager. To start and stop listening to heading events, you call the
startUpdating
Heading
and
stopUpdatingHeading
methods accordingly.
Just as with location updates, heading updates are managed via delegate methods: n
locationManager:didUpdateHeading:
—
Called whenever a new heading is received that differs from the previous heading by more than the value specified in the
headingFilter
property.
n
locationManagerShouldDisplayHeading
Calibration:manager
—Called if your iPhone needs to be calibrated. This will typically happen only with a new iPhone where the compass has never been used. Returning
YES
will cause the compass calibration panel to appear.
You can dismiss the panel by calling
dismissHeadingCalibrationDisplay
, or you can prevent it from ever showing by returning
NO
to this method.
In the examples so far, you have concentrated on getting a single location as accurately as you can before stopping the location manager. You might want to have a real-world application that updates locations continuously, displaying the course, speed, and heading information as you walk or drive around. You will see an example of this in the “Putting It All Together” section later in this chapter.
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A
Adding the Map Kit framework to your project.
Code Listing 8.6 The header file for the map application.
About Map Kit
Map Kit, the mapping framework based on the Google Maps engine, gives you the ability to add interactive maps to your applications. Maps can be scrolled and zoomed to any region on the planet and can have pins, or annotations, added to the map to display additional information.
To add a map to your application:
1. Create a new view-based application, saving it as
MappingExample
.
2. In the Groups & Files pane, expand the
Targets section, right-click your application target, and select Get Info.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add
MapKit.framework
A
.
4. Open the MappingExampleView
Controller.h file, import the
MapKit
framework, and create an instance variable to hold your map view
(
Code Listing 8.6).
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5. Switch to the MappingExampleView
Controller.m file, uncomment the
viewDidLoad
method, and add the following code:
map = [[MKMapView alloc]
initWithFrame:[self.view
bounds]];
[self.view addSubview:map];
Code Listing 8.7 shows the updated code.
6. Build and run the application
B
.
That’s it—two lines of code, and you have a map! You should be able to navigate around the map and zoom in/ out by using the “pinch” gesture.
B
The application with a full-screen
MKMapView
.
Code Listing 8.7 The completed code for a bare-bones map application.
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C
Adding the Core Location framework to your project.
You’ll now update this code to make it a little more interesting.
To show your location on the map:
1. In the Groups & Files pane, expand the
Targets section, right-click your application target, and select Get Info.
2. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add
CoreLocation.framework
C
. Although this is not strictly necessary for this example, you will be using some convenience functions within the
CoreLocation framework.
3. Open MappingExampleViewController.m, and update your viewDidLoad method to set the map type to a satellite view and tell it to show the current location, indicated by an animated blue marker:
map.mapType = MKMapTypeSatellite; map.showsUserLocation = YES;
The outer circle on this marker indicates the accuracy of the location data—the wider the circle, the less accurate.
CLLocationCoordinate2D coords =
CLLocationCoordinate
2DMake(37.331689,-122.03071);
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4.
Next you create a variable to hold your map center coordinate, in this case
Apple’s headquarters:
float zoomLevel = 0.002;
MKCoordinateRegion region =
MKCoordinateRegionMake(coords,
MKCoordinateSpanMake(zoomLevel,
zoomLevel));
[map setRegion:[map regionThatFits:
region] animated:YES];
5. To zoom into a map, you need to create an
MKCoordinateRegion
.
This structure contains not only the coordinates the map should center on but also a span, which is comprised of a horizontal and vertical distance determining how much of the map
(in degrees) should be shown. A large span creates a zoomed-out view; a small span creates a zoomed-in view
D
.
Code Listing 8.8 shows the updated
viewDidLoad
method.
D
Displaying the current location on a map.
Code Listing 8.8 Updating the code to set and show a location.
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Just as with the iPhone’s native Maps application, you can display three possible maps with the mapType property:
MKMapTypeStandard —Shows a normal map containing street and road names. This is the default map type if none is specified.
MKMapTypeSatellite —Shows a satellite view.
MKMapTypeHybrid —Shows a combination of the two, in other words, a satellite view with road and street information overlaid.
When setting span values, depending on which map type you are using, you may be able to zoom in or out to a greater degree. For example, maps of MKMapTypeSatellite to zoom in a lot more than
generally contain greater detail and will allow you
MKTypeStandard .
Map Overlays
Map Kit allows you to overlay content over arbitrary areas of your maps. By using the
MKCircle
,
MKPolygon
, or
MKPolyline
class, you can easily define and draw shapes on your maps defined by coordinates.
Creating an overlay is a two-step process:
1. Create an overlay object (an object that conforms to the
MKOverlay
protocol), to which you assign one or more coordinate data points.
2. Create an overlay view object (an
MKOverlayView
subclass), which is used to visually represent the data in your overlay object.
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Now you’ll look at how you might go about updating the application, using overlays to draw a route on your map.
To draw a route on a map using overlays:
1. Open MappingExampleViewController.h, and add the
MKMapViewDelegate
protocol declaration to the
@interface
:
@interface MappingExampleView
Controller : UIViewController
<MKMapViewDelegate>
2. Open MappingExampleViewController.m, and add the following to the end of your
viewDidLoad
method:
map.delegate = self;
[self createRoute];
First you set the delegate of your
MKMapView
object, necessary since the map overlay is drawn in a delegate method.
You then call a custom method used to create the route information:
CLLocationCoordinate2D
routeCoords[5]; routeCoords[0] =
CLLocationCoordinate2DMake
(37.331689, -122.03071); routeCoords[1] =
CLLocationCoordinate2DMake
(37.331689, -122.03221); routeCoords[2] =
CLLocationCoordinate2DMake
(37.330259, -122.03221); routeCoords[3] =
CLLocationCoordinate2DMake
(37.330259, -122.03171); routeCoords[4] =
CLLocationCoordinate2DMake
(37.330519, -122.03055);
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E
Displaying a route on the map.
By using the MKCircle or MKPolygon class, you can define contiguous or closed regions on a map. These can then be filled with a color to indicate such things as country boundaries or other areas of interest.
MKPolyline *routeLine =
[MKPolyline polylineWith
Coordinates:routeCoords count:
pointCount];
[map addOverlay:routeLine];
[routeLine release];
You first create and populate an array with the coordinates of the points on your route. You then create an
MKPolyline
object and pass it your coordinates array. This will allow you to plot and draw lines between the coordinate points of your route. Finally, you add this to the map as overlay.
3. Implement the
mapView:viewForOverlay:
delegate method:
MKPolylineView *plView =
[[MKPolylineView alloc]
initWithOverlay:overlay]; plView.strokeColor =
[UIColor redColor]; plView.lineWidth = 5.0; return [plView autorelease];
This method is where you define how your route will actually be drawn.
You first create an
MKPolylineView
object, initializing it by passing it the overlay (the
MKPolyline
) you have already defined.
You then set the color and width of your line view and return it from the method, causing it to be drawn on the map.
Code Listing 8.9 shows the updated application.
4. Build and run the application.
You should see the same map as in the previous example, with a red line plotting a route
E
.
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Code Listing 8.9 The code updating to show a route.
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Adding annotations
To make your mapping applications richer and more interesting, you will often want to overlay information onto the map, and this is where annotations come in.
Map Kit contains support for adding not only simple “pin” annotations (as seen in the native iPhone Maps application) but also your own custom annotations that can have their own look and feel.
Adding annotations to a map involves a little more work than you’ve had to do so far.
To add an annotation to your map:
1. In the MappingExampleView
Controller.m file, you need to create your own custom class that implements the
MKAnnotation
protocol. At the very least, this class must implement the
coordinate
property ( Code Listing 8.10).
2. In
viewDidLoad
, set the delegate, and call a method to create your annotation by adding the following:
customAnnotation *annotation =
[[customAnnotation alloc]
initWithCoordinate:coords]; annotation.title = @"The Title"; annotation.subtitle = @"Subtitle";
[map addAnnotation:annotation];
[annotation release];
You’ve removed the
map.showsUser
Location = YES
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3. Finally, implement the
mapView:view
ForAnnotation:
delegate method to display the annotation as a pin:
MKPinAnnotationView *pinView =
(MKPinAnnotationView *) [map
dequeueReusableAnnotationView
WithIdentifier:annotation.title]; if (pinView == nil) pinView = [[[MKPinAnnotationView
alloc] initWithAnnotation:
annotation reuseIdentifier:
annotation.title] autorelease]; else pinView.annotation =
annotation;
Code Listing 8.11 shows the updated code.
Code Listing 8.10 The custom annotation class.
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Code Listing 8.11 The code updated to add a custom annotation.
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Code Listing 8.11 continued
Code Listing 8.12 Displaying an image as an annotation.
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F
Displaying an annotation on the map.
The
mapView:viewForAnnotation:
delegate returns an
MKAnnotationView
object. In this example, you are using the
MKPinAnnotationView
subclass that, as the name suggests, displays annotations as pins
F
. You can, however, return your own subclass if you want a different look and feel for annotations.
You can see the simplest example of this in
Code Listing 8.12. You set the
image
property on the base
MKAnnotationView
class.
This results in the map shown in
G
.
ing
Specifying a reuse queue when creat-
MKAnnotationView
objects allows the mapping engine to remove annotations from the map when they move off the screen (for example, if the user zooms or scrolls the map).
The annotation is taken out of the queue (also known as dequeuing) when it moves back on the screen.
You can also alter the look and feel of the annotation’s callout view (the view that shows up when the user touches the annotation) by overriding viewForCallout
AccessoryPosition : in your custom
MKAnnotationView class.
For more information on using annotations and overlays, refer to the “Annotating
Maps” section of the Location Awareness
Programming Guide.
G
A custom annotation showing a graphic.
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Adding reverse geocoding
Map Kit provides the facility to do lookups on latitude and longitude coordinates to get address information—a process known as reverse geocoding. You accomplish this via the
MKReverseGeocoder
class and its delegate methods.
In the previous example, you created your annotation manually, specifying the coordinates
title
and
subtitle
in the
viewDidLoad
method. You’ll now change your code to perform a reverse lookup of your position instead, creating an annotation with your address in its callout view.
To add reverse geocoding:
1. Open MappingExampleViewController.h, and add the
MKReverseGeocodeDelegate
protocol declaration to the
@interface
:
@interface MappingExampleView
Controller : UIViewController
<MKMapViewDelegate,
MKReverseGeocoderDelegate>
You also create an instance variable to hold your reverse geocoder:
MKReverseGeocoder *geo;
Code Listing 8.13 shows the updated header file.
Code Listing 8.13 The header file updated to add reverse geocoding.
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H
Displaying the address in an annotation.
2. Back in MappingExampleView
Controller.m, update the
viewDidLoad
method:
geo = [[MKReverseGeocoder alloc]
initWithCoordinate:coords]; geo.delegate = self;
[geo start];
Here you create your geocoder instance, set the delegate, and tell it to start the lookup.
3. Finally, you need to implement the
MKReverseGeocode
delegate methods, adding an annotation if you find an address:
[map addAnnotation:placemark];
[geo cancel];
and logging a console message on failure:
NSLog(@"geo error: %@",error);
[geo cancel];
Notice that you cancel the geocoder in both situations.
Code Listing 8.14 shows the completed code. Now your application shows the address
H
.
In the reverseGeocoder:didFindPlace mark:
delegate, you add an
MKPlacemark
as an annotation. This class contains properties to hold location information such as the city or state. Just like when you created your own custom annotation class in a previous example, this class implements the
MKAnnotation placed on a map.
protocol, so it can be
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Code Listing 8.14 The code updated to perform a reverse-geo lookup and add the address as an annotation to the map.
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A
The final completed mapping application.
Putting It All Together
So far you’ve seen how to get your location, draw and plot a location on a map, and perform reverse geocoding to get the address of a location.
Now you’ll combine all of these ideas into a single application that automatically updates as you walk or drive around. You’ll also add some fields to show your current address, compass heading, and distance traveled
A
.
To update your application:
1. In the Groups & Files pane, expand the
Targets section, right-click the application target, choose Get Info, and add
CoreLocation.framework.
2. Open MappingExampleViewController.h, import the Core Location framework header, and add the
CLLocationManager
Delegate
protocol.
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3. Now add some new instance variables:
CLLocationManager *lm;
UITextView *addressView;
UITextView *distanceView;
UITextView *headingView;
CLLocation *startingLocation;
CLLocation *lastPlottedLocation; double previousHeading;
The first holds the location manager, as in previous examples. Then you define a couple of views to display address distance information and the compass heading in your application. Finally, you need somewhere to hold your initial location when calculating the distance traveled, a variable to hold the last plotted location (so you can draw your route), and a variable to keep track of whether the heading has changed.
Code Listing 8.15 shows the header file.
Code Listing 8.15 The header file for the completed mapping application.
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4. In the MappingExampleView
Controller.m file, edit your
viewDidLoad
method to add all your new UI elements.
Set up the height of your address distance views and heading; then create a
CGRect
the same size as the main view:
float viewHeight = 25.0;
CGRect viewRect = [self.view
bounds];
You create a
CGRect
for your address view, at the bottom of your main view, and then set the color and alignment.
You do the same thing for the distance and heading views, placing them at the top of the main view:
CGRect addressViewRect =
CGRectMake(viewRect.origin.x,
viewRect.size.
height-viewHeight,viewRect.size.
width,viewHeight); addressView = [[UITextView alloc]
initWithFrame:addressViewRect]; addressView.backgroundColor =
[UIColor blackColor]; addressView.textColor =
[UIColor whiteColor]; addressView.textAlignment =
UITextAlignmentCenter;
You need to adjust the height and y position of the map to make room for the address and distance views:
viewRect.size.height -=
viewHeight*2; viewRect.origin.y += viewHeight;
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5. Next, add a couple of helper methods that are called when you get a new location event:
updateMapViewWithLocation: shouldZoom:
will update your map’s position.
updateGeoCoderWithLocation:
will create a new
MKReverseGeocoder
.
plotLocation:
will plot your current location on the map.
updateHeadingView
will be called whenever a new compass heading is received.
6. Finally, implement the delegates for the reverse geocoder, map overlay, and location manager. This allows you to update your map and address views whenever you receive a new location.
You also display an error dialog box if you fail to get a location.
Code List-
ing 8.16 shows the completed code.
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Code Listing 8.16 The completed mapping application code.
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Code Listing 8.16 continued
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Code Listing 8.16 continued code continues on next page
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Code Listing 8.16 continued
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Multimedia
The iPhone is a great portable multimedia device. It has a large, high-resolution display, a built-in camera (with video capture capabilities and multiple cameras on newer iPhones), directional audio, a powerful processor, and hardware support for playing all the common audio and video formats.
The “always-on” nature of the iPhone means that the media-rich Internet is never far away, and iTunes synchronizes with your computer so you can take your media with you. The multimedia frameworks of the iPhone SDK provide a comprehensive toolbox to use when adding these capabilities to your applications.
In this chapter, you’ll take a closer look at how to use these frameworks. You’ll learn to browse and retrieve images from the iPhone’s photo library, access and play audio from the iPod library, take pictures and video with the camera, and more.
In This Chapter
Playing Audio
Recording Audio
Using the iPhone’s Camera
Playing Video
Using the iPod Library
350
366
371
381
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Playing Audio
For playing audio in your applications, the iPhone SDK provides the
AVAudioPlayer
class, which lets you play sound in any audio format supported by the iPhone, including AAC, AIFF, MP3, and WAV. All the functionality you would expect with an audio player is available: You can play multiple sounds simultaneously, pause the audio, jump to any position, control the volume, loop the audio, and more. You can also access properties such as the current position, the duration, and metering information.
To create an application to play audio:
1. Create a new view-based application, saving it as AudioPlayerExample.
2. In the Groups & Files list, expand the targets section, right-click your application target, and select Get Info.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add
AVFoundation.framework
A
.
4. Open the AudioPlayerExampleView
Controller.h file, add the
#import
statement to import the AVFoundation.h file, and create an instance variable to hold the audio player ( Code Listing 9.1).
A
Adding the
AVFoundation
framework to your application.
Code Listing 9.1 The header file of the audio player application.
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Although
AVAudioPlayer
will work in most situations, it’s not suitable if your application needs to have streaming audio or requires low-level control over the audio. For more information on how to work with audio, refer to the Audio File Stream Services Reference and Core Audio sections of the iPhone developer documentation.
5. Switch to the AudioPlayerExample
ViewController.m file, uncomment the
viewDidLoad
method, and add the following:
NSString *filePath = [[[NSBundle
mainBundle] resourcePath]
stringByAppendingPathComponent:
@"song.mp3"];
NSURL *fileURL = [NSURL
fileURLWithPath:filePath];
NSError *error = nil; audioPlayer = [[AVAudioPlayer
alloc]initWithContentsOfURL:
fileURLerror:&error]; if (error)
NSLog(@"Error: %@",error); else audioPlayer.play;
This retrieves the audio file (named song.mp3 here) from the application bundle and then creates and initializes a new
AVAudioPlayer
with the audio file.
6. Build and run the application.
The audio will play as soon as the application starts. It may be rather loud since the default value for the
volume
property is 100 percent.
Code Listing 9.2
shows the updated code.
Code Listing 9.2 The completed code for the audio player application.
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Providing more control
Now you’ll update this application to add
Play, Pause, and Stop buttons. You’ll also add a volume slider and a control to jump, or scrub, to any position in the audio file
B
.
To add controls to the audio player:
1. In the AudioPlayerExampleViewControl ler.h header file, add the some instance variables that you’ll use for your user interface:
UIButton *playButton;
UIButton *stopButton;
UISlider *volume;
UISlider *scrubber;
UIProgressView *currentPosition;
NSTimer *timer;
2. Switch to the AudioPlayerExample
ViewController.m file, and in the
view
DidLoad
method, remove the call to the
play
method, since you don’t want your audio to start playing until you tell it to. Set the following properties on the audio player:
audioPlayer.volume = 0.3;
[audioPlayer prepareToPlay];
This sets the starting volume to be 1/3 maximum (volumes are measured as a value between 0 and 1.0). Then it calls the
prepareToPlay
method, which sets up the audio player and preloads its buffers. This is an important step to make sure your audio starts playing as soon as possible after its
play
method is called.
3. The
createControls
method is used to create the user interface. You create buttons for playing and pausing your audio, and another for stopping. You also create sliders to control the volume and to act as an audio scrubber.
B
The updated application showing the new controls.
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Notice how the continuous property of the volume control is set to Yes. This allows you to adjust the volume without removing your finger from the screen while the audio continues playing.
4. Next, implement the
play:
method which is called when the Play/Pause button is tapped:
if (! audioPlayer.playing)
{ audioPlayer.play;
[playButton setTitle:@"Pause"
forState:UIControlStateNormal];
} else
{ audioPlayer.pause;
[playButton setTitle:@"Play"
forState:UIControlStateNormal];
}
You can use the
playing
property to check to see whether the audio player is playing. If so, pause the audio player, and switch the button title to Play. If not, begin playing, and change the title of the button to Pause.
5. Implement the
stop
method:
audioPlayer.stop; audioPlayer.currentTime = 0;
[playButton setTitle:@"Play"
forState:UIControlStateNormal];
This stops the audio and resets the position to start. It also resets the text of the
Play button in case the Stop button was tapped while the audio was paused.
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6. Implement the
changeVolume:
method that is called from your slider:
audioPlayer.volume = volume.value;
This sets the
volume
property of the audio player to the slider’s current value.
7. Finally, implement the
scrub:
method, which uses the
currentTime
property of the audio player to move to a different place in the audio.
8. Build and run the application.
You can now play, pause, and stop the audio; adjust the volume; and jump to any position as the audio track plays.
Code Listing 9.3 shows the completed code.
Code Listing 9.3 The completed audio player code.
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Code Listing 9.3 continued
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Responding to audio events
When you receive a call on your iPhone, it automatically mutes any audio that you’re currently playing. The iPod application pauses your music, and once the call is complete, your audio continues playing right where it left off.
You can add this functionality to your own applications by adopting the
AVAudioPlayerDelegate
protocol and implementing its methods. This is also how you’ll update the application to reset all the controls once the audio has finished playing.
To update the application to respond to events:
1. Open the AudioPlayerExampleView
Controller.h file, and add the declaration to implement the
AVAudioPlayerDelegate
protocol ( Code Listing 9.4)
You also add a Boolean instance variable that you’ll use to determine whether any audio was playing when the call came in.
Code Listing 9.4 Adding the
AVAudioPlayerDelegate
protocol declaration to the header file.
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2. Switch to the AudioPlayerExample
ViewController.m file, and update the
viewDidLoad
method, setting the delegate on the audio player:
audioPlayer.delegate = self;
3. Implement three delegate methods
(
Code Listing 9.5).
The
audioPlayerBeginInterruption:
will be called if the audio is interrupted by a call. You use a Boolean variable to track whether the audio was playing.
The
audioPlayerEndInterruption:
will be called once you end the call.
Here you check the Boolean set in the previous delegate and resume playing if necessary.
The
audioPlayerDidFinishPlaying: successfully:
delegate is called when the audio finishes. Here you call a method to reset all the controls (
Code
Listing 9.6).
Code Listing 9.5 Implementing the
AVAudioPlayerDelegate
methods.
Code Listing 9.6 The
resetControls
method sets all the audio controls back to their initial states.
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Playing audio in the background
As part of the multitasking support introduced with iOS4, the iPhone is now capable of playing audio in the background. When a user exits your application, any currently playing audio will continue to play (unless, of course, another application starts with its own audio).
Note that at the time of writing, the iPhone
Simulator does not currently support background audio; you will have to test your code on an actual iPhone.
To update the application to play audio in the background:
1. In the Groups & Files pane, expand the target section, right-click your application target, and select Get Info.
2. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add
AudioToolbox.framework
C
.
3. Open AudioPlayerExampleView
Controller.h, and add the
#import
statement to import AudioToolbox.h
( Code Listing 9.7).
4. Switch to AudioPlayerExampleView
Controller.m, and add the following just before you create your audio player:
OSStatus status =
AudioSessionInitialize
(NULL, NULL, NULL, NULL);
UInt32 sessionCategory =
kAudioSessionCategory_
MediaPlayback; status = AudioSessionSetProperty
(kAudioSessionProperty_
AudioCategory, sizeof
(sessionCategory),
&sessionCategory);
AudioSessionSetActive(YES);
C
Adding the AudioToolbox framework.
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D
Updating the info.plist file.
Code Listing 9.7 The updated header file.
This code is sets up an audio session for playing back media (as defined by
kAudioSessionCategory_MediaPlayback
).
By using this category, your audio will continue to play when your application exits or when the screen locks.
The final step in getting background audio is to make a change to your application’s info.plist file.
5. In the Groups & Files pane, select the
Resources section, and then select
AudioPlayerExample-Info.plist.
6. Right-click in the key column, and select
Add Row. Select “Required background modes” from the list
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7. Expand the key you have just added, click the arrows to the right of Item 0, and select “App plays audio”
E
.
8. Build and run your application.
If you start the song playing and then press the Home button to exit your application, the audio will continue to play.
Code Listing 9.8 shows the updated
viewDidLoad
method.
E
Setting the key in the info.plist file to enable background audio.
Code Listing 9.8 The updated
viewDidLoad
method for the background audio player example.
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Controlling audio from the background
You’ve seen how to make your audio continue to play in the background even after your application has exited, but sometimes you might want to be able to control that audio. For example, you might have written a music player and still want to be able to change tracks and control the audio volume while running another application.
Again, the multitasking features of the iOS4
SDK make it very easy for you to add this to your applications.
To update the application to control audio from the background:
1. Open AudioPlayerExampleViewControl ler.m, and add the following line to your
viewDidLoad
: method:
[[UIApplication sharedApplication]
beginReceivingRemoteControl
Events];
This tells your application that it can receive events from the external audio controls when it is running in the background.
2. Since remote audio events are sent via the responder chain, you must make sure that your view controller is capable of receiving them. This is done by implementing the following method:
- (BOOL)canBecomeFirstResponder
{
return YES;
}
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You’ll also will need to make sure that your view controller is always the first responder after any user interaction has taken place, so in your
play:
,
changeVolume:
, and
scrub:
methods, you need to add the following:
[self becomeFirstResponder];
3. Finally, you implement the
remote
ControlReceivedWithEvent
: method to capture remote control events:
switch (event.subtype)
{ case UIEventSubtypeRemoteControl
TogglePlayPause:
[self play:nil]; break;
}
In this example, since you have only a Play/Stop button, you handle the
UIEventSubtypeRemoteControl
TogglePlayPause
event; however, there are other events you can test for, such as skipping to the next chapter or seeking forward and backward through the movie.
Code Listing 9.9 shows the completed application.
4. Build and run your application.
If you start playing the song and then press the Home button to exit the application, the audio will continue to play as previously. However, this time, if you double-tap the home button and swipe the multitasking area to the right, you will bring up the audio controls
F
. You can stop and start the audio by tapping the Play/Pause button. Notice also how your application icon has automatically appeared in the control–tapping it will open your application.
F
background audio.
G
Controlling
Controlling the volume of background audio from the lock screen.
In the example here, you used the multitasking audio controls to control your application’s audio when in background mode.
You can also control the audio from external the iPod controls. To do so, make sure your application audio is playing and then doubletap the home button from the lock screen to bring up the iPod controls. One advantage of controlling audio from here is that you also get a volume slider.
G
.
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Code Listing 9.9 The completed background audio player example.
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Code Listing 9.9 continued
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Code Listing 9.9 continued
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Recording Audio
Recording audio on the iPhone is handled in much the same way as playing audio, only this time you use an instance of the
AVAudioRecorder
class. You can record audio of any length (assuming you have enough file space on the iPhone), pause and resume recording, or specify a recording of a specific length of time.
Just as with the
AVAudioPlayer
class, you can also determine the amount of time the recording has been running and access data about the audio levels (for input levels rather than output, obviously). Delegate methods handle interruptions to recording in the same way as the audio player.
To create an application to record audio:
1. Create a new view-based application, saving it as AudioRecorderExample.
2. In the Groups & Files list, expand the targets section, right-click your application target, and choose Get Info.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add
AVFoundation.framework
.
4. Open the AudioRecorderExample.h file, add the
#import
statement to import the
AVFoundation.h file, and create instance variables to hold an audio recorder and an audio player ( Code Listing 9.10).
Code Listing 9.10 The header file for the audio recorder application.
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5. Switch to the AudioRecorder
Example.m file, uncomment the
viewDidLoad
method, and add the following:
NSArray *paths = NSSearchPathFor
DirectoriesInDomains(NSDocument
Directory, NSUserDomainMask, YES);
NSString *documentsDirectoryPath =
[paths objectAtIndex:0];
NSString *filePath = [documents
DirectoryPath stringByAppending
PathComponent: @"myRecording.
caf"];
NSURL *fileURL = [NSURL file
URLWithPath:filePath];
NSError *error = nil; audioRecorder = [[AVAudioRecorder
alloc] initWithURL:fileURL
settings:nil error:&error]; if (error)
NSLog(@"error: %@",error); else
{
[audioRecorder prepareToRecord];
[self createControls];
}
This retrieves the documents directory and then specifies a file path where you can save your recording.
Next, you create a new audio recorder object, and if there aren’t any errors, you tell the audio recorder to prepare itself for recording. This ensures that recording begins as soon as possible after the
record
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Notice that you pass
nil
for the
settings
parameter, causing the audio recorder to be created with its default settings. (This parameter is discussed in the
“Controlling recording settings” sidebar.)
6. You next call the
createControls
method, which creates a user interface consisting of a Play button and a Record button.
7. The
record:
method is called when the user taps the Record button, toggling the recording on and off and updating the button title.
8. Similarly, the
play:
method checks to see whether recording is taking place, and attempts to play back the newly recorded audio.
Notice how you check for and release the audio player instance. This is necessary because you are loading the newly created recording each time you press play.
Code Listing 9.11 shows the completed code.
9. Build and run the application.
You may need to run it on an iPhone if you don’t have a microphone on your computer for the simulator to use.
Code Listing 9.11 The completed audio recorder code.
For a complete list of the settings available to audio recorders, refer to the AVAudioRecorder Class Reference in the iPhone developer documentation.
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Code Listing 9.11 The completed audio recorder code.
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Controlling recording settings
In the “To create an application to record audio” exercise, you used the default recording settings to create the audio recorder by passing nil to the settings parameter. In most situations, this will be all you need, but audio recorders give you much more granular control over the recording, letting you set properties such as sample rate, number of channels, audio quality, bit rate, and more.
To configure audio settings, construct an NSDictionary of key-value pairs, and assign it to the
settings
property of your audio recorder. Code Listing 9.12 shows the viewDidLoad method updated to set the audio quality, bit rate, number of channels, and sample rate of the recording.
Code Listing 9.12 Defining some values for the recording settings property.
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Using the iPhone’s
Camera
You use the
UIImagePickerController
class to let users choose images from the iPhone’s photo library and capture images or even video (if supported) from the built-in camera.
UIImagePickerController
is a view controller subclass, providing all the controls necessary for choosing and taking pictures and movies. As a developer, you simply create an instance of the class, set some properties, implement the delegate methods, and then tell the image picker to display. The control handles everything else for you.
The user selects an image or takes a picture (or movie), which is returned to the delegate. You then dismiss the image picker, returning control to your application.
You can let users edit an image or trim a movie by setting the
allowsEditing:
property to
YES
. Doing so returns an
NSDictionary
(along with the image or movie) to the delegate containing information about any edits that were made.
Setting the
sourceType
property of an image picker determines the type of interface displayed. There are three possible source types: n n n
UIImagePickerControllerSourceType
PhotoLibrary
—This displays an interface that allows the user to select an image or movie from their photo library.
UIImagePickerControllerSourceType
SavedPhotosAlbum
—This displays an interface that allows the user to select an image or movie from the camera roll or from the Saved Photos folder.
UIImagePickerControllerSourceType
Camera
—This displays an interface that allows the user to take a picture or record a movie using the iPhone’s camera.
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Since the same control is used to pick images from the photo library and take pictures or record movies, you should check the source type is supported before trying to use it. You do this by using the
isSourceTypeAvailable:
class method, which returns a Boolean indicating whether a source type is supported. The iPod touch, for example, doesn’t have a camera and would return
NO
for the source type
UIImagePickerControllerSourceTypeCamera
.
To create an application with an image picker:
1. Create a new view-based application, saving it as ImagePickerExample.
2. Open the ImagePickerExample.h file, and add the
UINavigation
ControllerDelegate
and
UIImagePickerControllerDelegate
protocol declarations. You also create an instance variable to hold the image picker ( Code Listing 9.13).
Code Listing 9.13 The header file for the image picker application.
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3. Switch to the
ImagePickerExample.m
file, uncomment the
viewDidLoad
method, and add the following:
imagePicker = [[UIImagePicker
Controller alloc] init]; imagePicker.delegate = self; imagePicker.allowsEditing = YES;
UIButton *photoLibraryButton =
[UIButton buttonWithType:
UIButtonTypeRoundedRect];
[photoLibraryButton setFrame:
CGRectMake(100,10,120,34)];
[photoLibraryButton setTitle:
@"Photo Library" forState:
UIControlStateNormal];
[photoLibraryButton addTarget:
self action:@selector
(photoLibrary
ButtonClick:) forControlEvents:
UIControlEventTouchUpInside];
[self.view addSubview:
photoLibraryButton];
This creates the image picker controller instance, setting the delegate and allowing users to edit any images they pick. You then create a button that will be used to launch the image picker.
4. Implement the method that is called when the button is tapped:
[self presentModalViewController:
imagePicker animated:YES];
Since you are neither checking nor setting a source type, the default source type of
UIImagePicker
ControllerSourceTypePhotoLibrary
will be used.
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5. Implement the
imagePickerController: didFinishPickingMediaWithInfo:
and
imagePickerControllerDidCancel:
delegates with the same code:
[picker dismissModalView
ControllerAnimated:YES];
This hides the image picker when the user selects an image or closes the image picker by tapping the Cancel button. At this stage, you will not be doing anything with the image returned from the picker.
Code Listing 9.14 shows the completed code.
Code Listing 9.14 The completed code for the image picker application.
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A
Browsing the photo library.
If you run the application in the simulator and tap the button, you should be presented with a new display
A
. You can browse through the photo library and edit the image before selecting.
By setting the source type to
UIImagePickerControllerSourceType
PhotoLibrary
, you can use the isSourceTypeAvailable
property to determine whether the user’s photo library is empty (it will return
NO
).
When recording movies, you are limited to a maximum of ten minutes. If the movie is longer, the user will have to trim it using the built-in editing controls before saving.
Taking photos and video
You’ve seen how to select photos from the photo library. Now you’ll update the application by adding a button that lets the user take a photo or, if supported by the iPhone, a video. You’ll also enhance the code to check that both the photo library and the camera are available as source types and, if not, display an error message
B
.
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Capturing photos and video with the iPhone.
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To update the application to take a photo or video:
1. Update the
viewDidLoad
method to check for the availability of both camera and video support on the iPhone:
if ([UIImagePickerController
isSourceTypeAvailable:
UIImagePickerControllerSource
TypeCamera])
{
NSArray *availableMedia =
[UIImagePickerController
availableMediaTypesForSourceType:
UIImagePickerControllerSource
TypeCamera]; imagePicker.mediaTypes =
availableMedia;
}
This code retrieves the array of supported media types using the
availableMediaTypesForSourceType
class method. An iPhone with video support will have two elements in the array: one for the camera and one for video. Older iPhones will have only the camera element.
You then assign this array to the
mediaTypes
property. Notice the result of writing the
availableMedia
array to the console for an iPhone with video support
C
.
C
The available camera media for an iPhone 3GS.
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2. Create a second button for taking photos and videos:
UIButton *cameraButton =
[UIButton buttonWithType:UIButton
TypeRoundedRect];
[cameraButton setFrame:CGRectMake
(100,60,120,34)];
[cameraButton setTitle:@"Camera"
forState:UIControlStateNormal];
[cameraButton addTarget:self
action:@selector
(cameraLibraryButtonClick:)
forControlEvents:
UIControlEventTouchUpInside];
[self.view addSubview:cameraButton];
3. Update the
photoLibraryButtonClick:
method to check that the source type is available:
if ([UIImagePickerController
isSourceTypeAvailable:
UIImagePickerControllerSource
TypePhotoLibrary])
{ imagePicker.sourceType =
UIImagePickerControllerSource
TypePhotoLibrary;
[self presentModalViewController:
imagePicker animated:YES];
} else
[self displaySourceError];
If the source type is not available, the preceding code will display an error message.
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4. Implement the code for the
camera
LibraryButtonClick:
method to launch the image picker in camera mode :
if ([UIImagePickerController
isSourceTypeAvailable:UIImage
PickerControllerSourceType
Camera])
{ imagePicker.sourceType =
UIImagePickerControllerSource
TypeCamera;
[self presentModalView
Controller:imagePicker
animated:YES];
} else
[self displaySourceError];
Notice that you check that the camera is available before setting the source type to display the camera interface in the image picker.
Code Listing 9.15
shows the completed code.
5. Build and run the application.
You will need to run the application on an iPhone because the simulator doesn’t support the camera as a source type.
Code Listing 9.15 The updated camera application.
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Code Listing 9.15 The updated camera application.
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If your iPhone has video capabilities, you should now see the video button available in the bottom-right corner of the screen
D
.
By inspecting the
mediaType
key, you can determine the type of media captured.
After selecting a picture, you’ll see
UIImage
s for both the original image and the edited image
E
. The area cropped by the user is represented as an
NSRect
.
Now check out the same console output resulting from creating a movie
F
. This time you see the path where the movie was saved.
D
When using the camera, the video button is available for iPhones with video support.
E
Console output after taking a picture with the iPhone camera.
380 Chapter 9
F
Console output after recording a movie with the iPhone camera.
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Playing Video
You can add support for playing video by using the
MPMoviePlayerController
class; the process is similar to playing audio.
Movies either can be a local file or can be streamed over HTTP from a remote source.
The movie controller will play all the iPhone-supported formats, including MOV,
3GP, MPV, and MP4. You can also play MP3 and AAC audio files; the movie controller will display the QuickTime logo on a white background in place of the movie.
The area in which a movie is played is determined by the
view
property of the movie controller. Just as with any other view, you can manipulate its frame and incorporate it into your view hierarchies.
You can even overlay subviews on top of the movie and set custom background content via the
backgroundView
property.
By setting the
scalingMode
property of the movie, you can control how a movie that is wider or higher than the iPhone screen is displayed. This process is similar to how scaling works with the
UIImageView
class; you can have the movie either fully fill the display or scale by width or height and show a border for the other dimension.
You have full control of the movie playback, including things such as starting and stopping, seeking forward and backward through the movie, and setting which controls appear onscreen to manipulate the playback of the movie. You can even choose to remove these onscreen controls entirely, which may be useful when playing an intro movie to a game.
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Knowing that many developers wouldn’t require this level of control, Apple created the
MPMoviePlayerViewController
class.
This provides a simple view controller for displaying movies full-screen and is very easy to implement in your applications.
To create an application to play a movie:
1. Create a new view-based application, saving it as MoviePlayerExample.
2. In the Groups & Files list, expand the targets section, right-click your application target, and select Get Info.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add
MediaPlayer.framework
A
.
4. Open the MoviePlayerExampleView
Controller.h file, add the
#import
statement to import the MediaPlayer.h file, and create an instance variable to hold the movie player view controller (
Code
Listing 9.16).
5. Switch to the MoviePlayerExample
ViewController.m file, uncomment the
viewDidLoad
method, and add the following:
UIButton *btn = [UIButton
buttonWithType:UIButtonType
RoundedRect];
[btn setFrame:CGRectMake
(100,110,120,34)];
[btn setTitle:@"Show Movie"
forState:UIControlStateNormal];
[btn addTarget:self action:
@selector(buttonClick:
forControlEvents:UIControl
EventTouchUpInside];
[self.view addSubview:btn];
A
Adding the
MediaPlayer
framework to your application.
Code Listing 9.16 The header file for the movie player view controller application.
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Here you are simply creating a button that, when tapped, will call a method to load the movie.
6. Next implement your
buttonClick
: method:
NSString *filePath = [[[NSBundle
mainBundle] resourcePath]
stringByAppendingPathComponent:
@"movie.m4v"];
NSURL *movieURL = [NSURL
fileURLWithPath:filePath];
This code should look familiar: It’s almost exactly the way you set up and play audio. You first retrieve the video file from the application bundle. (This example assumes you have added a movie named movie.m4v to your project.)
playerViewController =
[[MPMoviePlayerViewController
alloc] initWithContentURL:movieURL];
You then create your movie player view controller, using the
NSURL
object you’ve just created.
[[NSNotificationCenter
defaultCenter] addObserver:self
selector:@selector
(moviePlayerDidFinish:)
name:MPMoviePlayerPlayback
DidFinishNotification
object:[playerViewController
moviePlayer]];
[self presentMoviePlayerView
ControllerAnimated:playerView
Controller];
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Next you set up a method that will be called when the movie finishes playing before finally presenting the movie itself. Notice you don’t have to actually tell the movie to start playing—this is done automatically for you.
7. Implement the
moviePlayerDidFinish
: method:
MPMoviePlayerController
*player = [aNote object];
[[NSNotificationCenter
defaultCenter]
removeObserver:self
name:MPMoviePlayerPlaybackDid
FinishNotification
object:player];
[player stop];
[self dismissMoviePlayerView
ControllerAnimated];
[playerViewController release];
Here you are just cleaning up by removing yourself as an observer to the movie view controller, making sure the movie has stopped and any memory it’s using is released.
Code Listing 9.17 shows the completed application.
Notice how you have a full set of onscreen controls for the movie, and you can switch between landscape and portrait modes by simply rotating the phone
B
.
B
Playing a full-screen movie using a movie player view controller.
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Code Listing 9.17 The completed code to play a movie using a movie player view controller.
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To gain more control over movie playback
You’ve seen how easy it is to play movies by using instances of the
MPMoviePlayerViewController
, but sometimes you may want to have more control over the appearance of your movies. As previously mentioned, you can gain a lot more control of the visual elements of your movies by using an instance of the
MPMoviePlayerController
class.
If you have a large movie or are streaming a movie across a network, it may take some time before the movie is ready to be played. Movie players handle this situation by preloading some of the movie into a buffer and then sending a notification once the movie has loaded enough to be played. By responding to this notification, you can display a progress indicator to the user that disappears only when the movie is actually ready to be played.
Now you’ll see how to use these notifications to display an indicator that shows before the movie begins and then hides itself once the movie is ready to play. You’ll load the movie from a network location to see how HTTP streaming works. You’ll also learn how to manipulate some of the properties of the movie view to create a more custom experience.
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To update the application to use an MPMoviePlayerController:
1. Open MoviePlayerExampleView
Controller.h, and create a new instance variable to hold your activity indicator
( Code Listing 9.18)
2. Switch to MoviePlayerExampleView
Controller.m, and modify the
viewDidLoad
method:
CGRect activityFrame =
CGRectMake(130,10,40,40); activityView = [[UIActivity
IndicatorView alloc] initWith
ActivityIndicatorStyle:
UIActivityIndicatorViewStyle
Gray];
[activityView setFrame:
activityFrame];
[self.view addSubview:
activityView];
Here you are creating and adding an activity indicator that you’ll use to indicate that the movie has not loaded.
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Code Listing 9.18 The header file for the updated movie player application.
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3. Update the
buttonClick:
method:
NSURL *movieURL = [NSURL
URLWithString:@"http://images.
apple.com/movies/us/hd_
gallery/gl1800/480p/mammoth_
480pr.mov"]; playerController = [[MPMovie
PlayerController alloc]
initWithContentURL:movieURL]; playerController.should
Autoplay = NO; playerController.initial
PlaybackTime = 5.0; playerController.controlStyle =
MPMovieControlStyleEmbedded;
This time you are loading your movie from the Internet rather than using a local movie. Next you create your movie player in the same way as the earlier example, except now you are using an
MPMoviePlayerController
instance.
4. You then set some properties that control whether the movie starts playing automatically, determine the start position (in this example, five seconds in), and indicate the type of movie playing controls you want to show.
playerController.backgroundView.
backgroundColor = [UIColor
yellowColor];
CGRect playerFrame =
CGRectInset(self.view.bounds,
50.0, 50.0); playerController.view.frame =
playerFrame;
[self.view addSubview:player
Controller.view];
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Next you set the background color of your movie—the area of your
MPMoviePlayerController
that does not contain the playing movie. You then set the actual frame of the movie player controller and manually add it to your main view as you would any other
UIView
. Note that although the movie will not begin loading itself from the network at this point, it will not actually show until it’s ready to play, either.
5. Finally, you subscribe to the same notification as earlier, in addition to a new one:
MPMoviePlayerLoadState
DidChangeNotification
is called whenever the network buffering state of the movie changes. This is indicated by enabling animation for the activity indicator.
6. Implement the
loadStateChange
: method:
MPMoviePlayerController *player =
[aNote object]; if(player.loadState ==
MPMovieLoadStatePlayable ||
MPMovieLoadStatePlaythroughOK)
[activityView stopAnimating]; else
[activityView startAnimating];
This method will be called whenever your movie changes its network state.
By examining the
loadState
property, you can determine whether the movie is ready to be played and show or hide your activity indicator.
Code Listing 9.19 shows the completed code.
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7. Build and run the application.
This time the movie does not load right away but instead shows an activity indicator while it is downloaded from the network. Once enough of the movie has downloaded, the activity indicator disappears, and you can tap the play button to start the movie. The activity indicator will automatically appear again if the movie has difficulty streaming from the network.
Note how the movie shows a different set of controls from the earlier example
C
. You can still make the movie go fullscreen by tapping the resize button. Also note how the movie is locked into portrait mode and doesn’t automatically switch to landscape when the iPhone is rotated.
You can read more about working with video by referring to the MPMoviePlayer-
Controller and MPMoviePlayerView-
Controller class references in the iPhone developer documentation.
C
Playing a movie in a custom movie player.
Code Listing 9.19 The updated movie player code loading a movie from a network location and responding to notifications.
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Code Listing 9.19 continued
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Using the iPod library
You’ve already seen how to play movies using the Media Player framework.
This framework also lets you access the iPhone’s iPod library from within your own applications. You can play all the library’s audio content, including music, podcasts, and audio books. You can also get access to all the playlists in the iPod library, including genius, on-the-go, and smart playlists, as well as those created in iTunes. You will need to run the examples in this section on an iPhone because the simulator has no iPod library.
Accessing media items
Every song, podcast, and audio book in the iPod library is known as a media item, and each media item is an instance of the
MPMediaItem
class, which represents a single piece of media. Each media item contains a unique, persistent identifier along with a set of other metadata containing information such as the song title, artist, genre, and so on.
To retrieve media items from the iPod library, you create a media query, specifying filter criteria based on the items you are trying to retrieve. You can optionally specify a media grouping, which will group and sort the returned media items by a common property such as artist, playlist, or genre. Media queries offer a number of predefined initializer methods that prepopulate the grouping type property for you.
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A
Sample console output of a media query.
To create an application to retrieve media items from the iPod library:
1. Create a new view-based application, saving it as iPodLibraryExample.
2. In the Groups & Files list, expand the targets section, right-click your application target, and select Get Info.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add
AVMediaPlayer.framework
.
4. Open the iPodLibraryExample.h file, and add the
#import
statement to import the MediaPlayer.h file.
5. Switch to the iPodLibraryExample.m file, uncomment the
viewDidLoad
method, and add the following code:
MPMediaQuery *query =
[MPMediaQueryartistsQuery];
NSArray *results = [query items]; for (MPMediaItem *m in results)
NSLog(@"%@",[m valueForProperty:
MPMediaItemPropertyTitle]);
This creates a media query for all media items, grouping by artist, and stores the media items in the variable
results
.
You then loop through the array, using the
valueForProperty:
method to log the title of each media item to the console
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To update the code to add a filter for a particular artist, add the following:
MPMediaQuery *query =
[MPMediaQueryartistsQuery];
MPMediaPropertyPredicate *pred =
[MPMediaPropertyPredicate
predicateWithValue:@"Dylan"
forProperty:MPMediaItemProperty
Artist
comparisonType:MPMediaPredicate
ComparisonContains];
[query addFilterPredicate:pred];
NSArray *results = [query items]; for (MPMediaItem *m in results)
NSLog(@"%@",[m valueForProperty:
MPMediaItemPropertyTitle]);
This is the same query but with a filter that returns only those media items with the word Dylan in their
Artist
property. You can add other filter criteria the same way. Notice the resulting console output
B
.
Creating a media query with no filter or grouping will return all media items from the iPod library.
Refer to the MPMediaItem Class Reference in the iPhone developer documentation for a complete list of metadata properties available for media items.
Accessing media collections
You can also use media queries to retrieve collections of media items grouped by a particular property, such as genre, album, artist, or playlist. This time you use the
collections
property of the media query.
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Sample console output after filtering the media query.
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C
Sample console output of a media query collection.
To use collections, modify the
viewDidLoad
method to look like the following:
MPMediaQuery *query = [MPMediaQuery
artistsQuery];
NSArray *results = [query
collections]; for (MPMediaItemCollection *m in
results)
{
MPMediaItem *item =
[m representativeItem];
NSLog(@"%@",[item valueForProperty:
MPMediaItemPropertyArtist]);
}
This time the array contains
MPMediaItem
Collection
objects. From this you can get the representative item, a media item whose properties represent the common properties of all media items in the collection. Since you are retrieving by artist, you know that all media items in the collection item will have the same artist. You then log the result to the console as you did earlier
C
. Notice how there are only two results since you had only two artists in your media query.
You can also use collections to retrieve playlists:
MPMediaQuery *query = [MPMediaQuery
playlistsQuery];
NSArray *results = [query
collections]; for (MPMediaPlaylist *m in results)
NSLog(@"%@",[m valueForProperty:
MPMediaPlaylistPropertyName]);
This time, you specify
playlistsQuery
as the initializer for the media query to return objects of type
MPMediaPlaylist
in the
collections
property, which you can loop through as before.
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Using the media picker
If you don’t want or need to go through the trouble of programmatically querying for media items, you can instead use the
MPMediaPickerController
view controller class. This provides you with a graphical interface similar to the iPod’s own media selection screen, allowing the user to pick media items just as they would with the iPod application. Once the user taps the
Done button, the media picker controller returns a collection of media items to your application.
To add a media picker to your application:
1. Open the iPodLibraryExample.h file, and add the declaration to implement the
AVAudioPlayerDelegate
protocol.
2. Switch to the iPodLibraryExample.m file, and edit the
viewDidLoad
method to create a button to launch the media picker:
UIButton *btnMedia = [UIButton
buttonWithType:UIButtonType
RoundedRect];
[btnMedia setFrame:CGRectMake
(230.0,410.0,80.0,34.0)];
[btnMedia setTitle:@"Media"
forState:UIControlStateNormal];
[btnMedia addTarget:self action:
@selector(mediaPickerAction:)
forControlEvents:UIControlEvent
TouchUpInside];
[self.view addSubview:btnMedia];
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D
The application with the media picker being used to select songs from the iPod library.
3. Implement the
mediaPickerAction:
method that is called when the button is tapped:
MPMediaPickerController *picker =
[[MPMediaPickerController alloc]
initWithMediaTypes:MPMediaType
Any]; picker.delegate = self; picker.allowsPickingMultipleItems =
YES; picker.prompt = @"Please select";
[self presentModalViewController:
picker animated:YES];
[picker release];
This initializes the media picker to show all media types. You can also filter the content in the picker to allow only music, podcasts, or audio books.
Setting
allowsPickingMultipleItems
lets the user select more than a single media item. You also set the title of the media picker.
4. Implement the
mediaPicker:didPick
MediaItems:
and
mediaPickerDidCancel:
delegate methods:
[self dismissModalViewController
Animated:YES];
This simply closes the media picker and logs any selected media items to the console
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Playing media
The
MPMusicPlayerController
class lets you play media items. Two types of music players are available: n
The application music player—This plays audio in your application only.
When your application ends, so does the audio. Using an application music player pauses any audio that happens to be playing on the iPod when your application was launched.
n
The iPod music player—This uses the iPhone’s iPod application to play the audio. When your application ends, the audio will continue to play, and the normal iPod functions control the playback. Using the iPod music player replaces any audio that happens to be playing on the iPod when your application was launched.
Both provide controls for playing, pausing, and stopping, as well as more powerful functions for fast-forwarding, rewinding, and skipping to the next, previous, first, and last songs. You can also access information about the song currently being played, allowing you to update your application interface accordingly.
To play audio, you pass the music player a set of one or more media items known as a playback queue. By using a playback queue, you can construct an ad hoc list of audio to play that doesn’t necessarily relate to any playlists or audio grouping in the iPod library.
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E
The completed media player application.
To play audio from the iPod library:
1. Open the iPodLibraryExample.h file, and create an instance variable to hold the music player:
MPMusicPlayerController *player;
2. Switch to the iPodLibraryExample.m file, and edit the
viewDidLoad
method to create the music player:
MPMediaQuery *query =
[MPMediaQueryartistsQuery]; player = [MPMusicPlayerController
applicationMusicPlayer];
[player setQueueWithQuery:query]; player.play;
This code creates a media query that’s grouped and sorted by artist. It then creates the application music player and passes the query to it before telling it to start playing.
Using the
setQueueWithQuery:
method is a convenient way to load a media player with media query results, but you might want to create a custom collection of music to play.
Now you’ll update the application to create a simple media player, add buttons to control the previous and next songs, and add a slider to control the song volume. You’ll also add some labels to display the current album artwork, artist name, song title, and track number. The media picker control will create the playlist for the application
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To update the application to create a media player:
1. Open the iPodLibraryExample.h file, and declare some new variables used to display the currently playing song
( Code Listing 9.20).
2. Switch to the iPodLibraryExample.m file, and modify the
viewDidLoad
:
songCount = 0; songNumber = 0;
[self createCurrentTrackDisplay];
[self createVolumeControl];
[self createPrevNextButtons];
[self createMediaPickerButton];
After initializing the variables you’ll be using to display the current track, you call methods to build the application’s UI:
The
createCurrentTrackDisplay
method adds an image view and labels to display information about the current track.
The
createVolumeControl
method adds a volume control to the interface.
This uses the
MPVolumeView
class, which is a special view that is designed to control your music player’s volume.
You don’t need to write any code other than adding this control to your interface; the slider is hooked up to your music player automatically.
Code Listing 9.20 The media player header file.
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The
createPrevNextButtons
method creates buttons that allow you to navigate forward and backward through the selected audio items. Notice they use the same action method,
prevNextAction:
. This method uses the
tag
property of the button to determine which button has been tapped. After checking that the action can be performed, it moves to the next or previous track and updates the
songNumber
variable used to display the current track.
3. Next assign the application player to a local variable (for convenience), and then register for the
MPMusicPlayer
ControllerNowPlayingItemDidChange
Notification
event:
player = [MPMusicPlayerController
applicationMusicPlayer];
[[NSNotificationCenter
defaultCenter] addObserver:self
selector:@selector(songChanged:)
name:MPMusicPlayerControllerNow
PlayingItemDidChangeNotification
object:nil]; player.beginGeneratingPlayback
Notifications;
The
songChanged:
method updates the interface each time a new media item begins playing. Calling
beginGenerating
PlaybackNotifications
tells the music player to post notifications whenever the media item changes.
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4. Finally implement the code for the
mediaPicker:didPickMediaItems:
delegate method:
[player setQueueWithItem
Collection:mediaItemCollection]; songCount = [[mediaItemCollection
items] count]; songNumber = 0; if (songCount > 0)
[player play];
This assigns the media collection the user has just picked to the music player using the
setQueueWithItemCollection:
method, resets the track count variables, and tells the music player to begin playing the first track.
Code List-
ing 9.21 shows the completed code.
Code Listing 9.21 The completed iPod library player application.
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Code Listing 9.21 continued code continues on next page
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Code Listing 9.21 continued
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Contacts, Calendars,
E-mail, and SMS
One of the great aspects of the iPhone is how the built-in applications can share data and work with each other. For example, when making a phone call in the Phone application, you select from a list of contacts created in the Contacts application.
In this chapter, you’ll learn how to use the APIs for interacting with some of the iPhone’s built-in applications: the Contacts,
Calendar, Mail, and SMS applications.
You’ll first learn how contact information is stored and how you can go about retrieving, creating, editing, and saving contacts in your own code. You’ll also see how you can replicate much of the user interface functionality of the Contacts application from within your own applications.
Next you’ll learn how you work with the calendar database and how to query for specific events, as well as create your own.
You’ll see how easy it is to create a user interface for working with events by using the built-in view controller classes. Finally, you’ll learn how to compose and send an e-mail and SMS and how the iPhone SDK makes adding this functionality to your applications almost trivial.
In This Chapter
Working with the Address Book
Adding a User Interface
The iPhone Calendar
SMS
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Working with the
Address Book
The Address Book is a system-wide database that stores all the information relating to contacts on the iPhone. Each record in the database is an instance of an
ABRecordRef
.
The Address Book can store two kinds of records: n n
Person records—Represented by the
ABPerson
type, these contain all the data relating to contacts such as names, phone numbers, and address information.
Group records—Represented by the
ABGroup
type, these are used to organize contacts into groups. Unlike person records, group records have only a single property, which represents their name.
To retrieve all records from the Address Book:
1. Create a new view-based application, saving it as AddressBookExample.
2. In the Groups & Files pane, expand the
Targets section, right-click your application target, and select Get Info.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add
AddressBook.framework
A
.
4. Open AddressBookExampleViewCont roller.h, and import the AddressBook.h header:
#import <AddressBook/AddressBook.h>
A
Adding the Address Book framework.
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B
Logging Address Book records to the console.
5. Switch to AddressBookExampleView
Controller.m, uncomment the
viewDidLoad
method, and add the following code:
ABAddressBookRef addressBook =
ABAddressBookCreate();
CFArrayRef allPeople = ABAddress
BookCopyArrayOfAllPeople
(addressBook);
CFArrayRef allGroups = ABAddress
BookCopyArrayOfAllGroups
(addressBook); for (id person in (NSArray *)
allPeople)
[self logContact:person]; for (id group in (NSArray *)
allGroups)
[self logGroup:group];
CFRelease(allGroups);
CFRelease(allPeople);
CFRelease(addressBook);
Here you first get a reference to the
Address Book using the
ABAddress
BookCreate
function. Then, using the
ABAddressBook CopyArrayOfAllPeople
and
ABAddress BookCopyArrayOf
AllGroups
functions, you retrieve all the contacts and groups in the Address
Book. Finally, you loop through each array, sending each record to a method that logs them to the console
B
.
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6. Implement the
logPerson:
method:
CFStringRef name = ABRecordCopy
CompositeName(person);
ABRecordID recId =
ABRecordGetRecordID(person);
NSLog(@"Person Name: %@ RecordID:
%d",name, recId);
Here you log the contact name and record ID to the console.
7. Similarly, implement the
logGroup:
method:
CFStringRef name = ABRecordCopy
Value(group,kABGroupName
Property);
ABRecordID recId =
ABRecordGetRecordID(group);
NSLog(@"Group Name: %@ RecordID:
%d",name, recId);
Here you log the group name and record ID to the console.
8. Build and run your application.
Code Listing 10.1 shows the completed code.
Notice in the example you used the
ABRecordCopyCompositeName
function to retrieve a contact’s name. Although you could have also retrieved their first and last names, this function is preferred since it takes into account not only the contact’s prefix (for example, “Dr.” or “Mr.”) but also the iPhone’s localization settings (for example, in which order to display first and last names).
The record ID of an Address Book record is unique and will remain with the record until it is deleted. However, if you sync your contacts with the MobileMe service and the sync data is reset, then the record ID for a record may change. For this reason, Apple recommends using a combination of the record ID and the contact name if you need to store a persistent reference to a contact.
In the previous exercise, you retrieved all the contact records in the Address Book.
You could also have retrieved contacts by name by using the
ABAddressBookCopy
PeopleWithName
function or retrieved an individual contact by using the
ABAddress
BookGetPersonWithRecordID
function.
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Code Listing 10.1 The completed code to loop through all Address Book records and log them to the console.
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Group records
You can use group records to organize contacts into related categories. The
Address Book framework provides a number of functions for working with them: n
By using the
ABAddressBookGetGroup
Count
function, you can find out the number of groups in the Address Book. n n
To retrieve an individual group, you can use the
ABAddressBookGetGroupWith
RecordID
function.
To get an array containing all the contacts in a group, you can use the
ABGroupCopyArrayOfAllMembers
function. n
To add and delete a contact to and from a group, use the
ABGroupAddMember
and
ABGroupRemoveMember
functions.
Code Listing 10.2 shows some examples of working with Address Book groups.
Code Listing 10.2 Some of the Address Book group functions.
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TABle 10.1 Single-value person properties
Constant kABPersonFirstNameProperty kABPersonLastNameProperty
Description
First name
Last name
kABPersonMiddleNameProperty kABPersonPrefixProperty kABPersonSuffixProperty kABPersonNicknameProperty kABPersonFirstNamePhonetic
Property kABPersonLastNamePhonetic
Property
Phonetic last name
kABPersonMiddleNamePhonetic
Property
Phonetic middle name
kABPersonOrganization
Property
Organization name
kABPersonJobTitleProperty
Phonetic first name
kABPersonDepartmentProperty kABPersonEmailProperty kABPersonBirthdayProperty
Job title
Department
E-mail address
Birthday
kABPersonNoteProperty
Middle name
Name prefix
(e.g., “Dr.”)
Name suffix
(e.g., “Jr.”)
Nickname
kABPersonCreationDate
Property kABPersonModificationDate
Property
Notes
Date contact created
Date contact last modified
Person records
Person records represent contacts in the
Address Book. Each contact has a number of properties to hold attributes such as their name, phone number, and address information. There are two kinds of properties: single-value properties and multivalue properties.
Single-value properties are used for simple information such as the contact’s name.
To retrieve a single-value property, you use the
ABRecordCopyValue
function.
For example, to get a user’s first and last names, you would use this:
CFStringRef firstName =
ABRecordCopyValue(person,
kABPersonFirstNameProperty);
CFStringRef lastName =
ABRecordCopyValue(person,
kABPersonLastNameProperty);
Notice the second parameter contains a constant representing the property name.
Table 10.1 lists the available properties.
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Multivalue properties are used to manage lists of values. A contact would generally have more than one phone number (for example, home, work, and cell phone numbers) and possibly multiple addresses (for work and home).
Retrieving multivalue properties is similar to retrieving single-value properties. You again use the
ABRecordCopyValue
function, only this time an
ABMultiValueRef
type is returned. You can then create an array containing a dictionary of values for each element by using the
ABMultiValue
CopyArrayOfAllValues
function:
ABMultiValueRef addrValues =
ABRecordCopyValue(person,
kABPersonAddressProperty);
NSArray *arrAddr = [NSArray
arrayWithArray:(id)
ABMultiValueCopyArray
OfAllValues(addrValues)];
You then loop through each of these elements to get the values:
for (NSDictionary *addr in
arrAddresses)
{
NSString *street =
[addr objectForKey:(NSString *)
kABPersonAddressStreetKey];
NSString *city =
[addr objectForKey:(NSString *)
kABPersonAddressCityKey];
NSString *state =
[addr objectForKey:(NSString *)
kABPersonAddressStateKey];
}
Now you’ll look at an example of how to create a new contact and how to set values for both single and multivalue properties.
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To create a new contact:
1. Create a new view-based application, saving it as ContactExample.
2. In the Groups & Files pane, expand the
Targets section, right-click your application target, and select Get Info.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add
AddressBook.framework.
4. Open ContactExampleViewController.h, and import the AddressBook.h header:
#import <AddressBook/AddressBook.h>
5. Switch to
ContactExampleViewController.m, uncomment the
viewDidLoad
method, and add the following code:
[self createPerson];
ABAddressBookRef addressBook =
ABAddressBookCreate();
CFArrayRef contacts = ABAddress
BookCopyPeopleWithName
(addressBook,CFSTR("Steve Jobs"));
ABRecordRef person = [(NSArray *)
contacts objectAtIndex:0];
[self logAddressesForPerson:
person];
You first call a method to create a sample contact. To test whether the contact was added successfully, you then query the Address Book for contacts matching the name of the newly added one and call a method to log the address to the console.
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6. Implement the
createPerson
method.
You first create a new person record and see some single-value properties:
ABRecordRef person =
ABPersonCreate();
CFErrorRef error = NULL;
ABRecordSetValue(person,
kABPersonFirstNameProperty,
@"Steve", &error);
ABRecordSetValue(person,
kABPersonLastNameProperty,
@"Jobs", &error);
Any errors in setting a property will be stored in the error variable; in this example, you don’t bother checking for errors.
7. Create a multivalue property representing the phone numbers, and set values for the main and mobile phone numbers:
ABMultiValueRef phoneRef =
ABMultiValueCreateMutable
(kABMultiStringPropertyType);
ABMultiValueAddValueAndLabel
(phoneRef,@"555-123-432",
kABPersonPhoneMainLabel,NULL);
ABMultiValueAddValueAndLabel
(phoneRef,@"554-987-321",
kABPersonPhoneMobileLabel,NULL);
ABRecordSetValue(person,
kABPersonPhoneProperty,
phoneRef,&error);
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8. Create another multivalue property, this time representing an address:
ABMutableMultiValueRef
addressRef = ABMultiValueCreate
Mutable(kABMultiDictionary
PropertyType);
NSMutableDictionary *dict =
[[NSMutableDictionary alloc]
initWithObjectsAndKeys:
@"1 Infinite Loop",
kABPersonAddressStreetKey,
@"Cupertino",
kABPersonAddressCityKey,
@"California",
kABPersonAddressStateKey,
@"95014",kABPersonAddressZIPKey,
@"USA",kABPersonAddressCountry
Key,nil];
ABMultiValueAddValueAndLabel
(addressRef,dict,kABHomeLabel,
NULL);
ABRecordSetValue(person,
kABPersonAddressProperty,
addressRef,&error);
Notice that this time you use the
kABMultiDictionaryPropertyType
type when creating the property. You then create a dictionary of key-value pairs representing the address; add this as the home address, and then save the address.
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9. Add the newly created contact to the
Address Book:
ABAddressBookRef addressBook =
ABAddressBookCreate();
ABAddressBookAddRecord
(addressBook, person, &error);
ABAddressBookSave(addressBook,
&error);
Notice the
ABAddressSave
function; this must be called in order to update the
Address Book correctly.
Code List-
ing 10.3 shows the completed code.
10. Build and run the application.
You should see the address of the newly added contact logged to the console. If you open the Contacts application, you should see your newly added contact
C
.
C
You can view the newly added contact in the
Contacts application.
Code Listing 10.3 The completed code to add a new contact.
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Adding a User
Interface
So far, you’ve seen how to programmatically work with the Address Book framework and how it takes quite a lot of code to perform even a relatively simple task such as adding a new contact. You can imagine that replicating an interface for something like the
Contacts application would be a lot of work.
Luckily, Apple thought about this and provides a second framework—the Address
Book UI framework—that enables you to use all the interface elements in the
Contacts application from within your own iPhone applications.
Picking people
The first element of the Address
Book UI framework you will look at is the people picker, represented by the
ABPeoplePickerNavigationController
class, which allows you to browse the
Address Book in the same way you do in the Contacts application
A
.
To create an application with a people picker:
1. Create a new view-based application, saving it as PeoplePickerExample.
2. In the Groups & Files pane, expand the
Targets section, right-click your application target, and select Get Info.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add both AddressBook.framework and
AddressBookUI.framework
B
.
A
The Contacts application displaying a people picker.
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B
Adding both Address Book frameworks to your project.
4. Open PeoplePickerExampleView
Controller.h, import the AddressBookUI.h header, and add the
ABPABPeople
PickerNavigationControllerDelegate
protocol declaration. You also create an instance variable to hold the people picker and create a button to launch the picker (
Code Listing 10.4).
5. Switch to PeoplePickerExampleView
Controller.m, uncomment the
viewDidLoad
method, and add the following code:
[self createUI]; picker = [[ABPeoplePicker
NavigationController alloc]
init]; picker.peoplePickerDelegate =
self;
Here you first call a method to create the user interface (a single button) and then create the people picker, setting its delegate to
self
.
6. Implement the
peoplePickerNavigation
Controller:shouldContinueAfter
SelectingPerson:
delegate method, which is called when a person is selected in the people picker:
[peoplePicker dismissModalView
ControllerAnimated:YES];
[self logPerson:person];
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Code Listing 10.4 The header file for the people picker application.
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Here you simply close the people picker and call a method to log the selected person to the console.
7. Build and run the application.
You should be able to select a person and see their name and record ID being logged to the console.
Code Listing 10.5
shows the completed code.
Code Listing 10.5 The completed people picker application.
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editing people
See how much easier it is to use a people picker rather than selecting contacts through code? Now you’ll see how you can display a contact’s details when the person is selected in the people picker, rather than simply closing the picker. You’ll also see how to use another class from the Address Book UI framework to visually edit your contact.
To update the application to allow editing of people:
1. Open PeoplePickerExampleView
Controller.h, and add some new instance variables:
UILabel *labelContactName;
UILabel *labelAddress;
UIButton *editContact;
ABPersonViewController
*editContactViewController;
UINavigationController *navEdit;
You add some controls you’ll use to display and edit the selected contact. The
ABPersonViewController
will provide the user interface for editing a person.
The navigation controller is necessary for correctly displaying the person view controller ( Code Listing 10.6).
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Code Listing 10.6 The updated header file for the people picker.
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2. Switch to PeoplePickerExample
Controller.m, and update the
viewDidLoad
method:
editContactViewController =
[[ABPersonViewController alloc]
init]; editContactViewController.
allowsEditing = YES;
UIBarButtonItem *closeButton =
[[UIBarButtonItem alloc]
initWithTitle:@"Close"
style:UIBarButtonItemStylePlain
target:self action:@selector
(closeEdit:)];
[[editContactViewController
navigationItem] setLeftBarButton
Item:closeButton];
[closeButton release]; navEdit = [[UINavigationController
alloc] initWithRootView
Controller:editContactView
Controller];
You first create a new
ABPersonView
Controller
, setting the
allowsEditing
property to true since you want to be able to edit the contact. You next create a bar button and add it to the person view controller’s navigation toolbar. This is necessary since this control does not actually provide any means of closing itself. Finally, you create the navigation controller required for correctly displaying the person view controller.
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3. Update the
createUI
method. In addition to adding some labels to display the selected contact’s name and address, you create a button you will use to edit them:
editContact = [UIButton button
WithType:UIButtonTypeCustom];
[editContact addTarget:self
action:@selector(editContact:)
forControlEvents:UIControlEvent
TouchUpInside];
[editContact setFrame:CGRectMake
(10,10,60,60)];
[editContact setEnabled:NO];
Notice how the button is of type
UIButtonTypeCustom
. This is because you will use the contact image as the background for the button. The button is initially set to disabled since you first need to select a contact with the people picker before you can edit it.
4. Implement the delegate methods used by the people picker. You first update the
peoplePickerNavigationController: shouldContinueAfterSelectingPerson:
delegate method you used earlier. By returning
YES
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5. Implement the
peoplePickerNavigation
Controller:shouldContinueAfter
SelectingPerson:property: identifier:
delegate:
[self updateNameLabelForPerson:
person];
[self updateImageViewForPerson:
person];
[self updateAddressLabelForPerson:
person]; editContactViewController.
displayedPerson = person;
[editContact setEnabled:YES];
[peoplePicker dismissModalView
ControllerAnimated:YES];
Here you call some methods to update the user interface with the details of the selected person. You also tell the contact view controller which person has been selected and enable the edit contact button (since you’ve now selected a contact) before closing the people picker
C
.
6. Implement the
editContact:
method that’s called when you tap the contact’s image:
[self presentModalViewController:
navEdit animated:YES];
Similar to when using the people picker, you tell the navigation controller to display, which in turn shows the person view controller and allows you to edit the contact.
C
Displaying the contact information.
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D
Editing contact details using an
ABPersonViewController
.
7. Implement the
closeEdit:
method, which is called when the user finishes editing:
ABRecordRef person =
editContactViewController.
displayedPerson;
[self updateNameLabelForPerson:
person];
[self updateImageButtonForPerson:
person];
[self updateAddressLabelForPerson:
person];
[navEdit dismissModalViewController
Animated:YES];
As when closing the people picker, you update the user interface to reflect any edits the user may have just made, before closing the navigation controller.
8. Build and run the application.
Notice how the people picker now drills down to a contact’s details. Once the people picker has closed, tapping the contact’s image allows you to edit their details
D
.
Code Listing 10.7 shows the updated code.
Just as the contact, the
ABPersonViewController provides a user interface to view and edit a
ABNewPersonViewController class allows you to add new contacts.
For more information on working with the Address Book and Address Book UI frameworks, refer to the Address Book Programming Guide for iPhone OS in the developer documentation.
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Code Listing 10.7 The people picker code updated to allow editing of the selected contact.
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Code Listing 10.7 continued
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The iPhone Calendar
Items in the iPhone calendar application are known as events and are represented by instances of the
EKEvent
class. You access data in the calendar database by using an
EKEventStore
object.
To retrieve events from the default calendar:
1. Create an
EKEventStore
object, which is used to access the calendar database:
EKEventStore *eventStore =
[[EKEventStore alloc] init];
NSDate *startDate = [NSDate date];
NSDateComponents *comp =
[[NSDateComponents alloc] init];
[comp setMonth:1];
NSCalendar *cal =
[[NSCalendar alloc] initWith
CalendarIdentifier:NSGregorian
Calendar];
NSDate *endDate = [cal dateBy
AddingComponents:comp toDate:
startDate options:0];
Next you create two date objects: one representing today and another for a month from today.
2. Create a predicate from these dates, and pass it to your event store object, returning an array of matching
EKEvent
objects:
NSPredicate *predicate =
[eventStore predicateForEvents
WithStartDate:startDate endDate:
endDate calendars:nil];
NSArray *matchingEvents =
[eventStore eventsMatching
Predicate:predicate];
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Code Listing 10.8 Querying the calendar event store.
Code Listing 10.8 shows an example of retrieving events from the default calendar for the next month.
To work with events, you will need to add the Event Kit framework into your application and import the EventKitUI/EventKitUI.h header file.
Notice how you pass nil in the calenders property when creating the predicate in the previous example. This tells the event store that you want to use the default calendar for your search. In this chapter, you will be working with the default calendar, but remember that it’s possible to have multiple calendars. You can retrieve these calendars as an array by using the property of an EKEventStore calenders
object.
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events
As previously mentioned, events are stored in the calendar database as
EKEvent
objects.
Events have many properties. Some of the more commonly used include the following: n n
eventIdentifier
—A unique identifier for the event
title
—An
NSString
representing the title of the event n n n n
startDate
/
endDate
—The start and end date of the event
alarms
—An array of
EKAlarm
objects, each one representing an alarm for the event
calendar
—The calendar to which the event belongs
location
—An
NSString
representing any location associated with the event n n
notes
—An
NSString
representing any notes associated with the event
recurrenceRule
—An
EKRecurrance-
Rule
object that describes the recurrence pattern for the event
Events can be added, updated, and removed from the calendar database via an
EKEventStore
object.
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To create an event for a birthday:
1. Create an event store you will use to add the event to the calendar database:
EKEventStore *eventStore =
[[EKEventStore alloc] init];
NSDateComponents *comp =
[[NSDateComponents alloc] init];
[comp setDay:1];
[comp setMonth:2];
[comp setYear:2010];
NSCalendar *cal =
[[NSCalendar alloc] initWith
CalendarIdentifier:NSGregorian
Calendar];
NSDate *eventDate =
[cal dateFromComponents:comp];
You also create an
NSDate
object representing the event date (in this case, Feb
1st, 2010—the author’s birthday!).
2. Next create a recurrance rule to determine the frequency of the event. Since this event is a birthday, you set the frequency to recur yearly:
EKRecurrenceRule *recurrance =
[[EKRecurrenceRule alloc] initRecurrenceWithFrequency:
EKRecurrenceFrequencyYearly
interval:1end:[EKRecurrenceEnd
recurrenceEndWithEndDate:
[NSDate distantFuture]]];
3. Create an
EKRecurranceRule
object.
Note how by using
[NSData distantFuture]
for the
end
property of the recurrence, you effectively say it recurs forever.
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4. Set an alarm by creating an
EKAlarm
object and setting it to occur one day before the event:
double alarmAmountInSeconds =
60.0 * 60.0 * 24.0;
EKAlarm *alarm = [EKAlarm
alarmWithRelativeOffset:(-1.0 *
alarmAmountInSeconds)];
5. Next create the actual event, and set some of its properties:
EKEvent *myEvent =
[EKEvent eventWithEventStore:
eventStore]; myEvent.calendar = eventStore.
defaultCalendarForNewEvents; myEvent.title = @"My Birthday"; myEvent.startDate = eventDate; myEvent.endDate = eventDate; myEvent.allDay = TRUE; myEvent.recurrenceRule =
recurrance; myEvent.alarms = [NSArray
arrayWithObject:alarm]; myEvent.notes = @"Remember to buy
a present!";
Note how you add it to the default calendar of the event store.
6. Finally, add the event to the event store and log its identifier to the console:
NSError *err = nil;
BOOL result = [eventStore
saveEvent:myEvent span:
EKSpanFutureEvents error:&err];
Code Listing 10.9 show an example of creating an event for a birthday.
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Code Listing 10.9 Creating an event.
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Viewing event details
Just as with the Address Book UI frameworks previously discussed, Apple provides the Event Kit UI framework for visually managing calendar events with a user interface similar to the built-in Calendar application.
The Event Kit UI framework offers two main classes: n
EKEventViewController—Displays details about the calendar event n
EKEventEditViewController—Is used to add and edit existing calendar events
Next you’ll see how to go about viewing details of a calendar event using the
EKEventViewController
class.
To create an application to view calendar events:
1. Create a new navigation-based application, saving it as EventViewExample.
2. In the Groups & Files pane, expand the
Targets section, right-click your application target, and select Get Info.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add both EventKit.framework and
EventKitUI.framework
A
.
4. Open RootViewController.h, and import the Event Kit headers. Here you also create two properties: an array to hold the calendar events and an
EKEventStore
object that will be used to access the calendar database ( Code Listing 10.10).
A
Adding the Event Kit frameworks.
Code Listing 10.10 The header file for the view event details example.
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5. Switch to RootViewController.m, uncomment the viewDidLoad method, and add the following code:
self.title = @"Events"; self.navigationController.
delegate = self; self.eventStore = [[EKEventStore
alloc] init];
Since you are working with a navigationbased application, the first thing you do is set the title before creating the calendar store object that you’ll be using to access the calendar database.
Finally, you call the method
refresh
SampleData
, which queries the data store for events occurring in the next month, before forcing the table view to reload.
6. Implement the
tableView
delegate methods.
tableView:numberOfRows
InSection:
simply returns the number of elements in the array. To return the actual data for your
tableView
, you implement the
tableView:cellForRow
AtIndexPath:
method:
EKEvent *event = [self.eventArray
objectAtIndex:indexPath.row]; cell.textLabel.text = event.title;
After extracting the event from the events array using the current
tableView
row, you use the title of the event as the title of cell. continues on next page
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7. Finally, implement the
tableView: didSelectRowAtIndexPath:
method, which will be called when you select a row:
EKEvent *event = [self.eventArray
objectAtIndex:indexPath.row];
[self viewEvent:event];
Again, you query the event array to find the event the user has selected and pass this to the
viewEvent
method:
EKEventViewController
*editController = [[EKEventView
Controller alloc] init]; editController.event = event;
[self.navigationController
pushViewController:
editController animated:YES];
[editController release];
Here you create an
EKEventView
Controller
object, set its
event
property to the value selected, and push it onto the navigation controllers stack.
8. Build and run your application.
You should see a list of events. Selecting one will display the details for the event
B
. Note that you might have to adjust the predicate defined in the
refreshSampleData
method if you don’t have any calendar events for the next month.
Code Listing 10.11 shows the completed code.
B
Viewing details of an event.
Code Listing 10.11 Viewing an event using an
EKEventViewController
.
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Code Listing 10.11 continued
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editing events
As mentioned, the Event Kit UI framework offers a second class (
EKEventEditView
Controller
) that you can use to add and edit calendar events. Now you’ll update the application to add this additional functionality.
To update the application to add and edit calendar events:
1. Open RootViewController.h, and add protocol declarations for
UINavigationControllerDelegate
and
EKEventEditViewDelegate
(
Code
Listing 10.12), which will allow you implement the methods required for editing of calendar events.
2. Switch to RootViewController.m, and update the
viewDidLoad
method:
UIBarButtonItem *addButton =
[[UIBarButtonItem alloc]
initWithBarButtonSystemItem:
UIBarButtonSystemItemAdd target:
self action:@selector
(addEvent:)]; self.navigationItem.rightBar
ButtonItem = addButton;
[addButton release];
Code Listing 10.12 The updated header file.
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First you tell the navigation controller that you want the current class to be the delegate. This is necessary since you need to refresh the table view when you edit or delete events.
You then create a navigation bar button that you will use to add new events. Notice that the call to
refreshSampleData
has been removed because you are now performing this in the
navigationController: willShowController:animated
method, which will be called when the navigation controller first loads.
3. Create the
addEvent:
method that is called when you press the navigation bar button:
EKEventEditViewController
*addController = [[EKEventEdit
ViewController alloc] init]; addController.eventStore =
self.eventStore; addController.editViewDelegate =
self;
[self presentModalView
Controller:addController
animated:YES];
[addController release];
Here you create an
EKEventEditView
Controller
object, which is used to add the event. Notice how you set its
eventStore
to the same event store being currently used by the other events. You also set the delegate, which is how you will be informed of events being added.
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4. Define the
eventEditViewController: didCompleteWithAction:
method, which is called when you have added a new event, and press Save:
if (action == EKEventEditView
ActionSaved)
{
[controller.eventStore saveEvent:
controller.event span:
EKSpanThisEvent error:nil];
[self refreshSampleData];
}
[controller dismissModalView
ControllerAnimated:YES];
You first check the
action
parameter to make sure the user is saving the new event and then tell the event store to save the new event. Notice how you also refresh the sample data to force the table view to redraw itself correctly. Finally, you make sure the
EKEventEditViewController
is properly dismissed.
5. Add the following to the
viewEvent
method:
editController.allowsEditing = YES;
Setting this property tells your
EKEventViewController
that you want to be able to edit events.
6. Implement the
navigationController: willShowViewController:animated:
delegate that is used to refresh the table whenever any data changes:
if (viewController == self)
[self refreshSampleData];
Here you do a quick check to make sure that you are showing the correct view controller. If so, you refresh the event data, causing the table view to refresh.
C
Editing an event.
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7. Build and run the application.
When you view an existing event, you should now see an edit button in the navigation bar. Tap it to edit the event details
C
.
Code Listing 10.13 shows the completed code.
Code Listing 10.13 The completed code for adding and editing calendar events.
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Although the iPhone SDK does not provide any means to receive e-mail, it does offer an API for sending e-mail. You can send e-mail from your applications in two ways.
The first is to create a specially formatted
URL that causes the Mail application to be launched:
NSString *mailString = @"mailto:
[email protected]?subject=test&body=
some content";
NSURL *mailURL = [NSURL URLWith
String:mailString];
[[UIApplication sharedApplication]
openURL:mailURL];
This technique has several drawbacks: n n
There is a limit to the length of the string that can be used via a
mailto:
URL, meaning your e-mail messages will need to be quite short.
You can’t attach files to the e-mail.
n
Your application will be closed, and the
Mail application will be opened. Once the e-mail has been sent, the user is left in the Mail application—not exactly the perfect user experience!
The second, preferred, option is to use the
MessageUI
framework, which provides a standard interface for composing and sending e-mails from within your applications via the
MFMailComposeViewController
class.
E-mails composed using this class are placed in the outbox of the Mail application so that even if the user doesn’t have network access, the message can be delivered at a later date. Unfortunately, this also means that the class doesn’t provide any notification about whether the e-mail is actually sent.
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(A third option is to use a third-party e-mail library such as the
skpsmtpmessage
class, available at http://code.google.com/p/ skpsmtpmessage .)
To create an application to compose and send e-mail:
1. Create a new view-based application, saving it as EmailExample.
2. In the Groups & Files pane, expand the
Targets section, right-click your application target, and select Get Info.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add
MessageUI.framework
A
.
4. Open EmailExampleViewController.h, import the MFMailComposeView
Controller.h header, and add the
MFMailComposeViewControllerDelegate
protocol declaration ( Code Listing 10.14).
A
Adding the
MessageUI
framework.
Code Listing 10.14 The header file for the e-mail application.
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5. Switch to EmailExampleViewController.m, uncomment the
viewDidLoad
method, and add the following code:
UIButton *compose = [UIButton
buttonWithType:UIButtonType
RoundedRect];
CGRect composeFrame =
CGRectMake(80,10,160,38);
[compose setFrame:composeFrame];
[compose setTitle:@"Compose Mail"
forState:UIControlStateNormal];
[compose addTarget:self action:
@selector(composeClick:)
forControlEvents:UIControlEvent
TouchUpInside];
[self.view addSubview:compose];
Here you are adding a button that calls the
composeClick:
method when tapped.
6. Implement the
composeClick:
method:
if ([MFMailComposeViewController
canSendMail])
The first thing you do is call the
canSendMail
class method to make sure you are capable of sending e-mail from your application. If the user has not configured their iPhone with an e-mail account, this method will return
NO
.
MFMailComposeViewController
*mailController = [[MFMail
ComposeViewController alloc]
init]; mailController.mailCompose
Delegate = self;
Next you create the mail compose view controller that will be used to present an interface to your user for composing their e-mail.
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NSArray *to = [[NSArray alloc]
initWithObjects:@"steve@apple
.com",@"[email protected]",nil];
[mailController setToRecipients:
to];
[to release];
Then you create an array of e-mail addresses to send the e-mail to and assign to the
mailController
using the
setToRecipients:
method. You can also set the CC and BCC recipients in the same way by using the
setCcRecipients:
and
setBccRecipients:
methods.
NSString *subject = @"some
subject";
[mailController setSubject:
subject];
NSString *body = @"An
<b>important</b> email.";
[mailController setMessageBody:
body isHTML:YES];
You then set the subject and the body of the e-mail. Notice how you can use the
isHTML
parameter to specify that the body contents are HTML.
NSString *filePath = [[NSBundle
mainBundle] pathForResource:
@"apple" ofType:@"png"];
NSData *fileData = [NSData
dataWithContentsOfFile:
filePath];
[mailController addAttachment
Data:fileData mimeType:@"image/
png" fileName:@"apple"];
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B
Composing an e-mail in your application.
You next attach a file to e-mail; in this example, it’s an image called apple.png located in the resources folder of the application bundle.
[self presentModalViewController:
mailController animated:YES];
Lastly, you show the compose interface
B
. The user is able to edit any of the mail settings (and of course, you need not have applied any settings before showing the compose interface). Notice how the signature is automatically appended to the mail body.
7. Implement the
mailComposeController: didFinishWithResult:error:
delegate method:
switch (result)
{ case MFMailComposeResultCancelled: break; case MFMailComposeResultSaved:
NSLog(@"mail was saved"); break; case MFMailComposeResultSent:
NSLog(@"mail was sent"); break; case MFMailComposeResultFailed:
NSLog(@"Error: %@",error); break;
}
[self dismissModalViewController
Animated:YES];
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This method will be called if either the
Cancel or Send button is tapped in the compose interface. You can check the result parameter to see what the user did. If the e-mail can’t be sent right away, it will be saved into the user’s outbox.
You can use the error parameter to check for any errors. Don’t forget to hide the compose interface in this method.
8. Build and run your application.
Since the simulator does not have any e-mail capabilities, you will have to run the application on an iPhone to test it.
Code Listing 10.15 shows the completed code.
Code Listing 10.15 The completed code for the e-mail application.
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Code Listing 10.15 continued
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SMS
As with sending e-mails, there are two methods you can use to send an SMS.
The first is to create a specially formatted
URL that causes the SMS application to be launched:
NSString *smsString = @"sms:5551234";
NSURL *smsURL = [NSURL URLWith
String: smsString];
[[UIApplication sharedApplication]
openURL:smsURL];
But as with sending e-mails, this results in a fairly poor user experience, since the user leaves your application and is forced into the SMS application.
A better technique is to use an
MFMessage
ComposeViewController
object, which works in a very similar manner to the previous e-mail example.
Just like sending an e-mail, you specify an array of recipients and the body of the
SMS. However, unlike sending e-mail, you cannot programmatically add attachments to the SMS. And of course, you don’t need to specify a subject.
To create an application to compose and send an SMS:
1. Create a new view-based application, saving it as SMSExample.
2. In the Groups & Files pane, expand the
Targets section, right-click your application target, and select Get Info.
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Code Listing 10.16 The header file for the SMS application.
3. Making sure the General tab is selected, click Add (+) at the bottom of the Linked Libraries list, and add MessageUI.framework.
4. Open SMSExampleViewController.h, import the MFMessageComposeView
Controller.h header, and add the
MFMessageComposeViewController
Delegate
protocol declaration (
Code
Listing 10.16).
5. Switch to SMSExampleViewController.m, uncomment the
viewDidLoad
method, and add the following code:
UIButton *compose = [UIButton
buttonWithType:UIButtonType
RoundedRect];
CGRect composeFrame =
CGRectMake(80,10,160,38);
[compose setFrame:composeFrame];
[compose setTitle:@"Compose SMS"
forState:UIControlStateNormal];
[compose addTarget:self action:
@selector(composeClick:)
forControlEvents:UIControlEvent
TouchUpInside];
[self.view addSubview:compose];
Here you are adding a button that calls the
composeClick:
method when tapped.
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6. Implement the
composeClick:
method:
if ([MFMessageComposeView
ControllercanSendText])
Just as in the example earlier, where you composed and sent an email, you first call the
canSendText
class method to make sure your device is capable of sending SMS.
MFMessageComposeViewController
*messageController =
[[MFMessageComposeViewController
alloc] init]; messageController.messageCompose
Delegate = self;
Next you create the SMS compose view controller that will be used to present an interface to your user for composing their SMS and set the delegate to the current class.
[messageController setBody:
@"Hello world!"];
Then you create the body of the SMS.
Note how, unlike the earlier e-mail example, you have not specified the recipients of the SMS because you are leaving this up to the user to do in the
SMS compose window. (Of course, you could have set this property by creating an array of phone numbers and using the
recipient
property.)
[self presentModalViewController:
messageController animated:YES];
Finally, you tell the view controller to show the SMS compose interface
A
.
Again as in the earlier example, the user is able to edit any of the SMS settings.
A
Composing an SMS in your application.
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7. Implement the
messageComposeView
Controller:didFinishWithResult:
delegate method:
switch (result)
{ case
MessageComposeResultCancelled: break; case MessageComposeResultSent:
NSLog(@"SMS was sent"); break; case MessageComposeResultFailed:
NSLog(@"SMS Failed to send"); break;
}
[self dismissModalViewController
Animated:YES];
This method will be called if either the Cancel or Send button is tapped in the compose interface. You can check the result parameter to see what the user did.
8. Build and run your application.
Since the simulator does not have any SMS capabilities, you will have to run the application on an iPhone to test it.
Code Listing 10.17 shows the completed code.
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Code Listing 10.17 The completed code for the SMS application.
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Multitasking
One of the most exciting new features in iOS4 is the introduction of multitasking.
Previously, the iPhone was capable of running only one application at a time, but now your application can continue to run in the background when you close it and switch to another.
In this chapter, you’ll get a brief overview of some of the multitasking features of iOS 4 and how they work.
In This Chapter
What Is Multitasking?
Responding to Local Notifications
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What Is Multitasking?
Quite simply, multitasking is the ability to do more than one thing at the same time.
On your desktop computer, for example, you might be running an e-mail client and a Web browser while simultaneously listening to music and downloading a file over FTP. Because your desktop operating system has been designed with multitasking at its core, all of these applications can essentially run at the same time with only minimal impact to the general system performance and each other.
Multitasking on the iPhone, however, is not quite the same as on the desktop.
Although powerful, the iPhone has limited memory, CPU, and other resources. Running multiple applications at once would quickly use up these system resources, resulting in applications becoming slow and unstable. Worst of all, your battery life could be significantly impacted.
Apple has gotten around this problem by implementing multitasking in a special way.
When you exit your application, instead of quitting, it is suspended and enters a special background mode. When your application resumes, you return immediately to where you were when you left, with all your application’s data and state preserved.
At any time, double-tapping the Home button causes the recently used apps to slide up from the bottom of the screen
A
. This dock shows icons of all the applications currently in background mode. Tapping an icon will instantly resume that application. (You can, of course, also resume your application by tapping its desktop icon.)
A
Applications running in the background are shown in the recently used apps area.
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B
You can prevent your application from multitasking using
<app>-Info.plist
.
Apple recommends that all developers implement multitasking in their applications.
In fact, it’s enabled by default. To prevent your application from multitasking, you must set the Application does not run in background key in the <app>-Info.plist
file of your application
B
. For more information, see the “Understanding application settings” section in Chapter 3, “Common Tasks.”
Some older iOS devices don’t support multitasking. You can use the multitasking
Supported property of the UIDevice class to determine whether multitasking is available.
entering and exiting background mode
If the operating system determines that it needs more memory, it may choose to terminate any background applications.
That’s why it’s important to understand the various phases an application goes through when entering and exiting background mode.
When your application switches to background mode, it goes through three distinct states: n
Active—Your application is running.
This is where you initiate the switch to background mode (usually by exiting the application).
n n
Inactive—Your application is no longer running and is transitioning to the background or suspended state.
Background—Your application is now either suspended or running one or more background services.
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There are some important application delegate methods to be aware of when working with multitasking: n
applicationDidEnterBackground:
is called when your application becomes inactive and begins to enter background mode. This is a good place for you to save any state information
(remember, the user or system may still terminate your application once it’s in background mode). It’s important to note that you only have approximately five seconds in which to perform any actions here before your application is fully suspended. n n n
applicationWillTerminate:
is called if your application is in the background but is not suspended, such as if it is monitoring location updates or using background audio. It’s important to note that if an application is in the background in suspended state and the user (or system) terminates the application, you will have no way of handling this.
applicationWillEnterForeground:
is called when your application comes out of background mode and begins to transition into becoming the running application. Your application is still inactive at this time, so this is a good place for you to reverse any changes you might have made when the application entered background mode.
applicationDidBecomeActive:
is called when your application becomes active as the current running application.
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Multitasking services
For the majority of applications, simply pausing when entering background mode is enough. However, some applications might need to continue to perform tasks while in background mode. For example, if you were listening to some audio and then switched to check your e-mail, you’d probably still want to be able to hear the audio.
For these situations, iOS 4 provides the following services.
Task completion
Imagine you have written an application that uploads files to a server. If the user puts your application into background mode, you would want to be able to finish any uploads that were taking place. For this scenario, you can use the task completion service.
Task completion provides you with a small amount of time (about ten minutes) to complete any long-running tasks before your application is suspended.
Long-running tasks are typically started from your application delegate’s
applicationDidEnterBackground:
method and must be wrapped in calls to
beginBackgroundTaskWithExpiration
Handler:
and
endBackgroundTask
.
For more information on task completion, see “Initiating Background Tasks” in the iOS Application Programming Guide .
Background location
If you are writing an application that needs to monitor a user’s location even when running in the background (such as a GPS mapping application), you can use the background location service.
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This service is enabled by setting the
Required Background Modes
key in the
<app>-Info.plist
file
C
. For more information, see the “Understanding application settings” section in Chapter 3.
Within your application, you can choose to monitor the user’s location in two ways: n
Standard location changes—This provides frequently updated information of a user’s location; however, it is not recommended for most applications running in the background since it uses a lot of battery power.
n
Significant location changes—This uses much less power. When the user’s position changes significantly (determined by the cellular radio of the device), your application will be briefly woken from background mode and given the new location information. Even better, if your application has been terminated, it is relaunched. The location event information will be passed in the
UIApplicationLaunchOptions
LocationKey
key of the options dictionary sent to the
application:DidFinish
LaunchingWithOptions:
method.
For more information on launch events, see the “Application Startup and Configuration” section in Chapter 3.
Background location tracking can have some privacy concerns because the user may not be aware an application is accessing their location. iOS 4 addresses these concerns in several ways: n n
Any application that wants to use location services must first request permission from the user
D
.
When an application is accessing location services, an indicator appears in the status bar
E
.
C
Enabling background location services.
D
Users must give permission for applications to use location services.
E
An icon in the top right of the toolbar shows that the current application is using location services.
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F
Applications using location services.
n
The user can disable location services on a per-application basis via the system settings. Additionally, an icon appears next to any application that has used location services within the last 24 hours
F
.
For more information on using location services, see the “About Core Location” section in Chapter 8, “Location and Mapping.”
Background audio
This service allows your application to continue to play audio while it is in background mode. A set of audio controls is available by launching the task-switching dock and swiping to the right
G
.
For an example of implementing background audio in your applications, see
Chapter 9, “Multimedia.”
Voice over IP (VoIP)
This service allows VoIP-based applications such as Skype to continue to receive and make calls when running from the background.
Local notifications
While push notifications were supported in previous versions, iOS 4 lets your application create local notifications. A notification can be scheduled to occur at any time in the future, and your application doesn’t even have to be running for the notification to occur.
G
The background audio controls.
Multitasking
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To create an application that uses local notifications:
1. Create a new view-based application, saving it as LocalNotificationExample.
2. Open LocalNotificationExampleView
Controller.m, uncomment the
viewDidLoad
method, and add the following code:
UIButton *btn = [UIButton
buttonWithType:UIButtonType
RoundedRect];
CGRect buttonRect =
CGRectMake(75,50,150,35);
[btn setFrame:buttonRect];
[btn setTitle:@"Create
Notification" forState:
UIControlStateNormal];
[btn addTarget:self action:
@selector(createNotification:)
forControlEvents:UIControlEvent
TouchDown];
[self.view addSubview:btn];
Here you are simply creating a button and adding it to your view.
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3. Implement the
createNotification:
method:
NSTimeInterval ss = 10;
NSDate *notificationDate =
[NSDate dateWithTimeInterval
SinceNow:ss];
First you create a date on which your notification should occur; in this example, set it to ten seconds from now.
UILocalNotification *note =
[[UILocalNotification alloc]
init]; note.fireDate = notificationDate; note.timeZone = [NSTimeZone
defaultTimeZone];
Next you create your notification, set its
fireDate
(the date on which it will occur), and set the time zone.
note.alertBody = @"The
Notification Body"; note.alertAction = @"View"; note.soundName = UILocal
NotificationDefaultSoundName; note.applicationIconBadgeNumber
= 1;
Next you set the text that will show in the notification pop-up as well as the label for the button that will launch your application. You also set a sound that will play when the notification appears as well as the badge number of your application icon.
NSDictionary *dict =
[NSDictionary dictionary
WithObject:@"Joe Smith"
forKey:@"username"]; note.userInfo = dict;
continues on next page
Multitasking
463
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You can pass additional information to your application by using the
userInfo
property. Here, you simply pass a string representing a username.
[[UIApplication sharedApplication]
scheduleLocalNotification:note];
Finally, you call schedule the notification with the system.
4. Build and run the application.
Tapping the button will cause a notification to be created. If you exit your application and wait, you should see the notification occur
H
.
Code Listing 11.1 shows the completed application.
H
A local notification. Notice the application icon also has a badge.
ptg
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Code Listing 11.1 Creating local notifications.
Multitasking
465
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Responding to local
Notifications
You’ve seen how easy to create a local notification, but that’s only one half of the puzzle. You also want to be able to respond to a local notification, possibly to capture any information passed in the
userInfo
dictionary.
This is all done by using a couple of the
UIApplication
delegate methods. Next you’ll see how to implement this.
To update your application to respond to local notifications:
1. Open LocalNotificationExampleApp
Delegate.m, and uncomment the
application:didFinishLaunchingWith
Options:
method:
UILocalNotification *note =
[launchOp objectForKey:
UIApplicationLaunchOptionsLocal
NotificationKey]; if (note)
NSLog(@"Notification info:
%@",note.userInfo);
Here you check the
launchOptions
dictionary for the key
UIApplication
LaunchOptionsLocalNotificationKey
, which will exist only if a local notification has been received. If it exists, you log the
userInfo
dictionary of the local notification to the console.
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2. Implement the
applicationDidBecome
Active:
delegate method:
application.applicationIconBadge
Number = 0;
This simply ensures your application badge number disappears (recall you set it when you created your local notification).
3. Finally, to handle notifications that occur when your application is either running or in background mode, implement the
application:didReceiveLocal
Notification:
delegate method.
Listing 11.2 shows the completed code.
4. Build and run your application.
This time when you create the notification, don’t exit the application. If you wait ten seconds, you should see your notification information being sent to the console
A
.
For more information on multitasking, see
“Executing Code in the Background” in the iOS Application Programming Guide .
ptg
A
Logging the contents of the
userInfo
dictionary.
Multitasking
467
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Code Listing 11.2 Responding to local notifications.
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index
Symbols
: (colon), using with methods, 7
{ } (braces), using in header (.h) file, 3
+ (plus) sign, prefixing class methods with, 7
[ ] (square brackets), using with methods, 5
A
ABGroup
type, using with Address Book, 406
ABPerson
type, using with Address Book, 406
accelerometer
creating tilt-sensitive applications, 307–310
determining orientation, 299, 301–302
redrawing for orientation changes, 303
updating for autorotation, 304–306
accelerometer data, smoothing out, 307
accessibility
accessibility attributes
Accessibility inspector, using with IB (Interface
accessible applications, creating, 99–100
action sheets
versus alert views, 145 changing appearance of, 145
actions
creating in IB (Interface Builder)
activity indicator view, creating, 140–141
Address Book
creating multivalue properties, 414–415
kABPerson*
logging records to console, 407, 409
record ID of records, 408 retrieving contact records in, 406–408
retrieving multivalue properties, 412
retrieving records from, 406–409
setting values for addresses, 415
setting values for phone numbers, 414
Address Book UI framework
adding labels for contact names, 423
displaying contact information, 424
AddressBookExampleViewController.h file, 406
addresses, displaying in map annotations, 339
alarms, setting in calendar, 432
alert messages, displaying, 142–143
alert views versus action sheets, 145
Index
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alloc
method
annotation callouts, altering, 337
annotation class, creating for maps, 334
annotations, displaying addresses in, 339
<app>Info.plist file
s
Apple Developer Connection Web site, 41, 307
application delegate, using, 84–86
application icons
key for, 88 removing “gloss effect” from, 88 application name, displaying, 88
application settings
application setup, setting unique identifier for,
applications. See also interapp communication; projects; settings page
creating settings page for, 91
with custom URL scheme, 104–105
launching from other applications, 103
setting version numbers for, 88
sharing information between, 105, 109–110
shipping with default settings files, 239–243
updating in IB (Interface Builder), 70–72
arrays
looping back through values of, 25
sorting for strings, 25 using @selector keyword with, 25
using with drill-down details application, 220
using with table views, 204–205
articles
array, using with parsed RSS feed,
asynchronous connections
updating applications for, 251–253
audio. See also background audio
controlling from background, 361–365
playing from iPod library, 399
playing in background, 358–360
audio controls, accessing, 362
audio events, responding to, 356
audio player application
checking playing status of, 352
implementing delegate methods, 357
implementing play: method, 352
implementing scrub: method, 354
implementing stop method, 352 preloading buffers, 352
resetting audio controls, 357 responding to events, 356–357
audio recorders
passing nil to settings parameter, 368, 370
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audio session, setting up, 359
audio settings, configuring, 368
AudioPlayerExampleViewController.h file, 350,
AudioRecorderExample.h file, 366
autorelease pools, using in memory
autoresizingMask
autorotation
AVAudioPlayer
class
AVAudioPlayerDelegate
protocol
B
background audio, controlling volume of, 362.
See also audio
background color
background location service, 459–461. See
also location manager background mode, entering and exiting,
battery power, preserving for location manager,
birthdays, creating events for, 431–433
bookmarks, using in Xcode IDE, 53
border styles, using with text fields, 156
bounds, using with views, 113–114
braces ({ }), using in header (.h) file, 3
breakpoints
adding in Xcode IDE, 52 removing in Xcode IDE, 52
Build Results window, displaying in Xcode IDE,
buttons
adding for alert views, 142–143
adding to applications, 170–171
creating for custom cells, 227
creating for taking photos and videos, 377
using target-action pattern with, 37
C
calendar event store, querying, 429
calendar events
calendars, using with dates, 22. See also
iPhone calendar
calendars
camel case notation, variation of, 5
camera mode, launching image picker in, 378
camera support, checking for, 376
capitalization, setting for keyboards, 158
categories, using as alternative to subclassing,
cells, customizing in table views, 224–232
CGRect
creating for frame of view, 113
checkbox buttons, creating, 172
class files, adding in Xcode IDE, 57
class methods
autoreleased objects returned by, 6 defining, 6 prefixing with plus (+) sign, 6 using, 6
classes. See also subclassing
Index
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classes (continued)
with methods for handling files, 234–235
clicks, capturing in web views, 169
CLLocation
events
CLLocationManager
class, delegate methods,
CLPreviewController
Cocoa Touch framework group, described, 2
code
displaying in functional groups, 52 hiding in Xcode IDE, 52
uncommenting in Xcode IDE, 53 code completion, using in Xcode IDE, 53
code-signing identities, resource for, 79
colon (:), using with methods, 7
Command key. See keyboard shortcuts compass, accessing in Core Location
contact information
contact names, adding labels for, 423
contact records, retrieving in Address Book,
ContactExampleViewController.h file, 413
contacts
creating for Address Book, 413–417
Contacts application
displaying people picker in, 418
Control key. See keyboard shortcuts controls
using UIControl class with, 170
copy
Core Location framework. See also location manager
adding logging of data to screen, 316–317
CLLocation
CLLocationManager
decreasing desiredAccuracy level, 323
handling location updates, 314–315
testing outside simulator, 315–316
Core OS framework group, described, 2
Core Services framework group, described, 2
CoreLocationExampleViewController.h file, 312,
D
data detectors, using with text views, 161
date and time intervals, calculating, 20–21
date objects, creating for calendar, 428
dates
calculating seconds between, 20–21 comparing, 20–21
getting day, month, and year from, 21
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Debugger Console
displaying location information in, 314
logging touch locations to, 294
defaults system, reading and writing to, 88
Delegate design pattern, using, 36
delegate methods
for CLLocationManager class, 314
implementing for alert view, 143, 162–163
implementing for page control, 133
using to manage heading updates, 324
design patterns
MVC (Model View Controller), 35
DetailViewController.h file, 218
developer, registering with Apple as, 41
dictionaries
populating from files, 28 verifying number of elements in, 28
directories
Documents
Library
tmp
documentation viewer, launching for iOS, 78
Documents
double-tap support, adding, 287
drill-down details application, main header file
e
editor pane in Xcode IDE, using, 50–51
EKEventViewController
composing and sending, 443–449
showing compose interface for, 447
EmailExampleViewController.h file, 444
event store
creating for birthdays, 431–433
F
files
editing in Xcode Organizer, 79
finding quickly in projects, 51 opening from keyboard, 51
reading in application bundles, 238
FilesExampleViewController.h file, 240
“flip” animation, using with modal views,
FlipModalExampleViewController.h file, 189
focus ribbon in Xcode IDE, explained, 52
font size, specifying for labels, 136
force-quitting applications, 90
Frame accessibility attribute, 101
frames, representing views as, 112
frameworks
adding to projects, 2 defined, 2 referencing in code, 2
French localization, displaying, 97
French strings file, adding to application,
Index
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G
Game Kit API, using for peer-to-peer
Get Info in Xcode IDE, keyboard shortcut,
GetWebContentViewController.h file, 248, 251
graphics
groups in Xcode
gutter in Xcode IDE, explained, 52
H
header (.h) file
@end
#import
@interface
line, 3 use of braces ({ }) in, 3
heading updates, checking support for, 324
helloWorld target in Xcode, features of, 46–47
helloWorldViewController.h file, 72
helloWorldViewController.xib file
Hint accessibility attribute, setting, 100–101
home directory, contents of, 237
HTTP authentication, responding to, 266
hyperlinks
handling in web views, 168–169 opening in Safari application, 169
I
IB (Interface Builder)
creating actions manually, 72–75
creating outlets manually, 72–75
displaying class’s actions, 70 displaying class’s outlets, 70
increasing width of time label, 73
inspector window, 67–69 laying out applications, 69
using to set styles for table views, 207
image picker
creating application with, 372–375
setting sourceType property of, 371–372
image views. See also views
controlling scrolling behavior of, 127
using with scroll views, 129–130
ImagePickerExample.h file, 372
images
choosing from photo library, 371
displaying as annotations, 336–337
getting paths of, 238 panning around, 130
using scroll view with, 129–130 zooming in and out of, 130
implementation (.m) file
@end
@implementation
#import
@synthesize
interapp communication, using openURL:
method in, 103. See also applications
interface, redrawing when rotating, 303
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Interface Builder (IB)
creating actions manually, 72–75
creating outlets manually, 72–75
displaying class’s actions, 70 displaying class’s outlets, 70
increasing width of time label, 73
inspector window, 67–69 laying out applications, 69
using to set styles for table views, 207
Internet connections, testing for, 252
iOS SDK (software development kit)
iPhone, displaying logging information on, 317
iPhone calendar. See also calendars
alarms
calendar
creating events for birthdays, 431–433
eventIdentifier
location
notes
recurrenceRule
retrieving events from, 428–429
startDate/endDate
title
viewing calendar events, 434–437 viewing details of events, 436–437
IPhone screen, adding logging location data to,
iPhone Simulator
adding photos to, 63 backing up data on, 63 features of, 61–63
removing applications from, 63 resetting, 63
iPhone vs. iPhone Simulator, building for, 58
iPhones, identifying via UDID, 79
iPod library
iPodLibraryExample.h file, 396, 399–400
iPods, identifying via UDID, 79
iTunes file sharing, support for, 88
J
JavaScript, executing in web views, 167
K
keyboard shortcuts
building applications in Xcode IDE, 58
code management in Xcode IDE, 52
force-quitting applications, 90
help in Xcode IDE, 53 jump-to-definition in Xcode IDE, 53
opening files in windows (Xcode), 51
Project Find window in Xcode IDE, 53
Single File Find in Xcode IDE, 53
Index
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keyboards
scrolling interface in response to, 162–163
setting capitalization for, 158
keyboardType
property
l
Label accessibility attribute, 101
label text
aligning, 138 displaying lines of, 138
labels
specifying font sizes for, 136
landscape versus portrait orientation, 186, 303,
language codes, resource for, 97
launch image, specifying name of, 88
launchOptions
layoutSubviews
method, using with table
Library
links
handling in web views, 168–169 opening in Safari application, 169
load screen, adding graphic for, 79 load time, speeding perception of, 79
loadView
local notifications. See also notifications
creating application for, 462–465
localization
localized applications, creating, 95–97
location aware applications, creating, 312–313
location events
location manager. See also background location service; Core Location framework
heading
location search, results of, 323
location updates, handling, 314–315
locations
setting and showing on maps, 328 showing in maps, 328
logging information, displaying on iPhone, 317
long-touch support, adding, 288–291
low-memory conditions, handling, 193. See
also memory management
M
.m (implementation) file
@end
@implementation
#import
@synthesize
Mail application, launching, 103, 443
MainWindow.xib, objects for, 76–77
map center coordinate, creating variable for,
Map Kit framework, adding to projects, 325
map overlays, creating, 329–330
mapping application
adding instance variables to, 342
creating CGRect for address view, 343
implementing delegates for, 344
MappingExampleViewController.h file, 325,
maps
adding annotations to, 333–337
adding reverse geocoding to, 338–340
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adding to applications, 325–327
displaying addresses in annotations, 339
removing annotations from, 337
showing locations on, 327–328 zooming into, 328
Maps application, launching and searching, 104
mapType
property, using to display maps, 329
media collections, accessing, 394–395
Media framework group, described, 2
media items
accessing in iPod library, 392–393
media picker
media player, creating, 400–404
media query, console output of, 393–394
MediaPlayer
memory management. See also low-memory conditions
MessageUI
method calls
methods
passing values into, 5 phrases used with, 5
use of square brackets ([ ]) with, 5
using colon (:) with, 7 writing, 7
MKCircle
MKMapView
MKPolygon
modal views, displaying, 189–193
Model View Controller (MVC) design pattern, 35
motion*
methods, using to detect shakes, 298
movement detection. See accelerometer
movie playback, controlling, 386
movie player, customizing, 387–390
movie player video controller
movie recording, time limitation of, 375
MoviePlayerExampleViewController.h file,
movies. See also videos
loading from network locations, 390–391
setting background color of, 389
showing activity indicator for, 390
MPMediaItem
MPMediaPickerController
view controller
MPMoviePlayerController:
MPMusicPlayerController
multitasking
preventing, 457 verifying capability for, 457
multitasking services
background audio, 461 background location, 459–461 local notifications, 461
multi-touch gestures. See also touch-based applications
pinch, 292–294 rotate, 292–294 supporting, 292–294 zoom, 292–294
MultiTouchExampleViewController.h file,
MVC (Model View Controller) design pattern, 35
Index
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N
Name
property, using with settings page, 93
navigation bar in Xcode IDE, using, 55–56
navigation controllers, using with table views,
network locations, loading movies from,
networking
creating peer-to-peer applications, 271–273
creating peer-to-peer chat applications,
responding to HTTP authentication, 266
retrieving content from web pages, 248
retrieving stock quotes from web pages,
sending data to web pages, 262
updating status on Twitter, 266–271
using asynchronous connections, 251–253
NIB (NeXT Interface Builder), 65
NIB Name property, using with
notifications. See also local notifications
described, 30 registering objects as observers for, 30
NSCalendar
NSData
NSDate
NSDate
NSDateFormatter
NSDictionary
loading and saving as file, 239–243
NSFileManager
NSHomeDirectory()
NSLog()
statements using with asynchronous connections,
NSMutableArray
NSMutableDictionary
NSNotification
NSNumberFormatter
NSString
class
format specifiers, 14 immutable quality of, 14
stringWithContentsOfURL:
using to read and write to URL, 18
NSTimer
NSURLConnection
NSUserDefaults
NSXMLParser
O
Objective-C
objects
calling release method for, 10–11
on/off controls, creating, 172–173
openURL:
method, using with UIApplication
Option key. See keyboard shortcuts orientation. See also landscape mode versus portrait orientation; view controllers
determining for shakes, 299–301
Portrait versus Landscape, 186
responding to changes in, 184–188
specifying for applications, 88
orientation changes, redrawing interface for, 303
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OrientationExampleViewController.h file, 304
outlets, creating in IB (Interface Builder)
Overview toolbar, using in Xcode IDE, 59
P
P2PExampleViewController.h file, 274
page control, creating for scroll view, 132–135
parser delegate methods, implementing, 256
parser
variable, using with RSS feed, 255
passwords, saving in settings file, 239–242
paths
getting array of filenames for, 236
retrieving for applications, 237
patterns. See design patterns
peer picker delegate method, implementing,
peer-to-peer applications, creating, 271–273
peer-to-peer chat application, creating,
people picker
adding to Address Book, 418–420
editing in Address Book, 421–427 updates for editing contacts, 426–427
PeoplePickerExampleViewController.h, 419, 421
phone numbers
setting values in Address Book, 414
photo library
determining empty status of, 375
photos
adding to iPhone Simulator, 63
picker views. See also views
pictures. See images; photos
pinch gestures, adding, 295–297
Play button, creating for audio, 368
playback queue, using with audio, 398
plus (+) sign, prefixing class methods with, 6
portrait versus landscape orientation, 186, 303,
PostTweetViewController.h file, 266
PostWebContentController. h file, 262
predicate, creating for search text, 214
preferences
application, 90 user, 87, 89–90
PreferenceSpecifiers key, using, 91
progress views, creating, 139–140
Project Find history, accessing in Xcode IDE, 53
projects. See also applications
properties
using getter methods with, 8 using setter methods with, 8
property list files, selecting in Xcode IDE, 50
provisioning profiles, use of, 79, 82
Q
QuartzCore framework, adding to long-touch
Quick Look framework
R
Record button, creating for audio, 368
recording settings, controlling, 370
rectangles. See CGRect referencing counting, using in memory
release
method, calling for objects, 10–11
responder objects, defined, 280
retain
Return key
changing text on, 158 hiding text field for, 158
reverse geocoding, adding to maps, 338–340
Index
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RootViewController.h file, 201, 204, 210, 218,
rotate gestures, adding, 295–297
rotating
rotation transforms, applying to views, 124–125
roundedCornerView
routes, drawing on maps, 330–332
rows
grouping into sections and styles, 204
indicating for custom cells, 230
RSS feeds
format of XML records for, 254
S
Safari application, opening links in, 169
saveClick:
scale transforms, using with views, 123–125
scope highlighting effect, using in Xcode IDE, 52
screen, adding logging location data to,
scroll views
adding zoom to, 131 paging content of, 131
using to zoom in and out of images, 130 using with images, 129–130
search text, creating predicate for, 214
segmented controls
Settings example, header for, 240
settings file
saving password in, 239–242 saving username in, 239–242
settings page
setting Name property for, 93 setting Title property for, 93
setView:
method, using with table views, 224
ShakeExampleViewController.m file, 299
shakes
determining orientation for, 299–301
Shift key. See keyboard shortcuts simulator. See iPhone Simulator
single-tap support, adding, 287
skpsmtpmessage
slider, configuring in IB (Interface Builder), 74
sliders
smart groups, creating in Xcode IDE, 48
SMS (Short Message Service)
composing and sending, 450–454
SMS application, launching, 103, 450
SMSExampleViewController.h file, 451
songs, selecting from iPod library, 397
splash screens, adding to applications, 86
square brackets ([ ]), using with methods, 5
startWiggle:
method, using with long-touch
status bar
choosing display styles for, 88 launching applications without, 88 leaving visible, 88
stock quotes, retrieving from web pages,
stopWiggle:
method, using with long-touch
string methods, common uses of, 19
strings
comparing, 15 converting case of, 15
creating arrays with substrings, 17
NSString
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performing case-sensitive comparisons, 15
replacing substrings in, 17 searching for substrings in, 17
strings file, adding to applications, 95–96
stringWithContentsOfURL:
subclassing, alternative to, 37–38. See also
classes substrings. See strings switches
altering appearance of, 173–174
creating for custom cells, 227
synchronous connection, explained, 250
system items
T
tab bar items
updating applications for use of, 196–199
tab view controllers, implementation files for,
tab views, using 194–199. See also views
table views. See also views
creating applications with, 201–203
creating arrays for sections of, 204–205
creating predicate for search text, 214
creating with drill-down behavior, 218–222
editable for searching, 210–216
implementing data sources for, 200 implementing delegates for, 200
setting styles in IB (Interface Builder), 207
suppressing delete button, 214
UITableView
UITableViewCell
using navigation controllers with, 217
tabs
adding graphics to, 196 adding titles to, 196
creating applications with, 194–195
limiting number of, 195 selecting in code, 195
tap counts,logging to Debugger Console, 286
tapCount
property, using with touch objects,
tappable links, converting data into, 161
tapping support
target-action pattern
targets in Xcode IDE
helloWorld, 46–47 using, 46–47
templates, choosing in Xcode IDE, 42–43
text fields
creating, 156–158 hiding for Return key, 158
removing text from, 157 resizing automatically, 157
restricting content entered into, 159–160
text views
using data detectors with, 161
thumb image, setting for UISlider, 175
TiltingExampleViewController.h file, 307
tilt-sensitive applications, creating, 307–310
Index
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time. See date and time intervals; World Clock application
timers
Title
property, using with settings page, 93
tmp
toolbar items, creating, 154–155
toolbars
autoresizingMask
touch locations, logging to Debugger Console,
touch-based applications. See also multi-touch gestures
adding long-touch support, 288–291
touch-based events, methods for, 280
TouchExampleViewController.h file, 281, 283,
Traits accessibility attribute, 101
tweetClick:
Twitter, updating status on, 266–271
U
UDID (unique device identifier), 79
UIApplication
class, using openURL: method
UIApplicationDelegate
UIBarButtonItem
UIButton
UIControl
UIDatePicker
UIDevice
UIDevice
singleton, using with shakes, 299
UIImage
UIImagePickerController
UIImageView
UILabel
class
retrieving for switches, 173–174
UIPageControl
, using with scroll views, 131
UISegmentedControl
UISlider
UISwitch
UITabBarController
UITableView
UITextField
UITextView
class
UIToolbar
UITouch
UIView
class
UIViewController
Unicode Consortium homepage Web site, 97
unique device identifier (UDID), 79
URL identifiers, support for, 88
URL scheme
responding to being launched via, 106–108
using in interapp communication, 103–105
user preferences
username, saving in settings file, 239–242
V
Value accessibility attribute, 101
version number, setting for applications, 88
video button, availability of, 380
videos. See also movies
view controllers. See also orientation
displaying modal views, 189–192
main views, 182 responsibilities of, 182
482 Index
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UIViewController
view-based applications, creating, 312
viewDidAppear
viewDidDisappear
viewDidLoad
method
viewDidUnload
views. See also image views; picker views; tab views; table views; web views
adding subviews to, 113, 117–118
animating properties of, 115–117
applying rotation transform to, 124–125 applying scale transform to, 124–125
creating custom rounded-corner, 120–122
locating origins of, 112 nesting, 112 overview of, 112
replacing with custom classes, 122
resizing via scale transform, 123
specifying origins and sizes of, 112
viewWillAppear
viewWillDisappear
VoiceOver
improving descriptions used by, 100–101
VoIP (Voice over IP) service, 461
volume, controlling for background audio, 362
W
Web pages
displaying in applications, 164–166
retrieving stock quotes from, 248–251
using Backward buttons in, 166 using Forward buttons in, 166
Web sites
Apple Developer Connection, 41, 307
registering as Apple developer, 41
skpsmtpmessage
Unicode Consortium homepage, 97
web views. See also views
loading local content, 168–169
Wi-Fi, setting property for, 88
X
Xcode IDE
adding classes to applications, 57
<app>-Info.plist properties, 44–45
Build and Go toolbar feature, 48
building and running applications, 58 building for iPhone vs. Iphone Simulator, 58
choosing project templates in, 42–43
Class hierarchy pop-up menu, 56
Index
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Xcode IDE (continued)
Errors and Warnings smart group, 45
find-and-replace operations, 53
Groups & Files pane, 44–45, 47
Included files pop-up menu, 56
Lock pop-up menu, 56 navigation bar, 55–56
SCM (source-code management) smart
selecting property list files, 50
Single File Find dialog box, 53
Tasks toolbar feature, 48 toolbar features, 48
Xcode Organizer
Archived Applications feature, 81
Devices section, 80 editing files in, 80
iPhone development area, 81–82
Provisioning Profiles feature, 82
Submit to iTunesConnect feature, 82
Validate Application feature, 81
XIB files
using with IB (Interface Builder), 65
XMLExampleViewController.h file, 255
Z
zoom gestures, adding, 295–297
zooming
adding to scroll view, 131 enabling, 131
484 Index
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