iPhone Open Application Development, 2nd Edition

Chapter 4. Event Handling and Graphics Services

In Chapter 3, you were introduced to some of the basic user interface elements of the iPhone. Many objects support high-level events such as buttonClicked and tableRowSelected to notify the application of certain actions taken by the user. These actions rely on lower-level mouse events provided by the UIView class and a base class underneath it: UIResponder. The UIResponder class provides methods to recognize and handle the basic mouse events that occur when the user taps or drags on the iPhone’s screen. These methods are incorporated into other events created in UIView to detect two-fingered gestures. Higher-level objects, such as tables and alert sheets, take these low-level events and wrap them into even higher-level ones to handle button clicks, row selection, and other types of behavior. All such screen-oriented events are processed using the Graphics Services framework, which provides screen coordinates, fingering information, and other data related to the graphics of the event.

This framework is considered to be low-level, and has since been built on with the more user-friendly touches API and other frameworks. These low-level functions tell the application exactly what has occurred on the screen and provide the information needed to interact with the user. They appear to be used largely in Apple’s own preloaded applications. To receive many of these events, you’ll need to add the following function call to your application: ...