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PART IV

Advanced iPhone
Programming Techniques
CHAPTER 14: Programming Multi-touch Applications
CHAPTER 15: Simple Animations
CHAPTER 16: Accessing Built-in Applications
CHAPTER 17: Accessing the Hardware

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14

Programming Multi-touch
Applications
WHAT YOU WILL LEARN IN THIS CHAPTER

➤

How to detect touches in your application

➤

How to differentiate between single and double taps

➤

How to implement the pinch gesture

➤

How to implement the drag gesture

One of the most important selling points of the iPhone is its screen, which can detect multiple
points of input. Multi-touch inputs allow for very natural interaction between users and your
applications. Because of multi-touch, the mobile Safari Web browser is easily one of the most
user-friendly Web browsers available on a smart phone.
In this chapter, you learn how to detect touches in your application and then implement some
cool features that improve the interaction between the user and the application, such as a
Jigsaw Puzzle application. By detecting touches in your application, the user can rearrange
the locations of the images on the screen, as well as change the size of the images using the
pinching gesture.

DETECTING TOUCHES
Before you learn how to detect touches in your application, you fi rst need to acquaint yourself
with a few events that handle the detection of touches. You will then be able to know whether
the user has single-tapped or double-tapped on your application and react accordingly.

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320

❘

CHAPTER 14

PROGRAMMING MULTI-TOUCH APPLICATIONS

Time to get the engine rolling! Make sure you download the code indicated here so you can work
through the following Try It Out activity.

TRY IT OUT

Detecting for Taps
[MultiTouch.zip] is available for download at Wrox.com

1.
2.

Using Xcode, create a new View-based Application project and name it MultiTouch.
Drag and drop an image into the Resources folder. Figure 14-1 shows an image named
apple.jpeg located in the Resources folder.

FIGURE 14-1

3.
4.

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Double-click the MultiTouchViewController.xib fi le to edit it in Interface Builder.
Populate the View window with the ImageView view. Ensure that the ImageView covers the entire
View window.

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Detecting Touches

5.

❘ 321

Select the ImageView view and view its Attributes window (see Figure 14-2). Set its Image
property to apple.jpeg.

FIGURE 14-2

6.

In the MultiTouchViewController.h fi le, add the following statements that appear in bold:
#import <UIKit/UIKit.h>

@interface MultiTouchViewController : UIViewController {
IBOutlet UIImageView *imageView;
}
@property (nonatomic, retain) UIImageView *imageView;
@end

7.

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Back in Interface Builder, Control-click and drag the File’s Owner item to the ImageView view.
Select ImageView.

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Get started developing iPhone apps
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•
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Wei-Meng Lee is Founder of Developer Learning Solutions, a technology company
specializing in hands-on training of the latest Microsoft and Apple technologies.
He writes extensively for online publications and is the author of Professional
Windows Vista Gadgets Programming and C# 2008 Programmer’s Reference.
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Explains how the fundamental concepts of outlets and actions allow
your code to interact with the visual elements in Interface Builder
Describes the use of the various views that make up the user
interface (UI) of your iPhone apps

Shows you how to build Tab Bar, Navigation, and Utility applications
Explores the powerful Table view and how it can be used to display
rows of data
Discusses using application settings to persist application preferences
Demonstrates how to implement multi-touch capability in your
iPhone application
Introduces the various techniques you can apply to develop animations
for the iPhone

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iPhone SDK and offers you a clear understanding of how
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required for creating your own iPhone applications. When you
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