Cocoa Touch™ for iPhone® OS 3

Chapter 11. Handling Touch Events

In This Chapter

Handling touch events in your custom UIViews

Implementing the methods needed to handle touch events

Learning about the UITouch class and how to use it

Configuring a UIView to receive multi-touch events

Extending the custom UIView sample code to handle touches and multi-touches

A defining feature of the iPhone is its use of multi-touch for its primary input. There is nothing more unique to iPhone than this capability. When working with custom views, it's important to utilize multi-touch to its greatest advantage. Fortunately, Cocoa Touch makes implementing a multi-touch interface on your custom views incredibly easy. All you have to do is override a few methods to handle the touch events to unlock the potential of this innovative capability.

In this chapter, you're going to take a look at how you implement multi-touch on a custom view. First, you will take a look at what you need to do to support multi-touch, and then you will implement multi-touch on your custom UIView example code from the last chapter.

Handling Touch Events in a Custom UIView

When the user's finger touches the iPhone screen, the view that the touch occurs within receives a set of messages. These messages are translated into calls to specific methods that are defined as part of the UIResponder class. UIView, as a subclass of UIResponder, also has the option to override these methods so that it can take action on these events. The methods that are called are touchesBegan:withEvent:, ...