Programming the iPhone User Experience

Chapter 6. Touch Patterns

The most famous feature of the iPhone and iPod Touch is the Multi-Touch interface. Multi-Touch allows a user to interact with a device using one or more fingers on a smooth, consistent physical screen. Touch-based interfaces have existed in prototypes and specialty devices for a while, but the iPhone and iPod Touch introduced the concept to the general consumer market. It’s safe to say that the interaction pattern has proven very effective and popular, inspiring other companies to implement similar systems on their devices.

Any new interface requires updated patterns for accepting and handling input and for providing feedback to users. Apple has identified several simple and intuitive patterns not entirely dissimilar from those for traditional mouse use, but specialized for a Multi-Touch interface. Paired with the conceptual patterns and physical hardware are several libraries developers can use to manage user interaction. The currency of Multi-Touch programming is the UITouch class, which is one of many related classes in UIKit.

In Cocoa Touch applications, user input actions like button presses trigger events. The iPhone OS processes a related series of touches by grouping them into Multi-Touch sequences. Possible key events in a hypothetical sequence are listed here:

• One finger touches the device

• A second finger optionally touches the device

• One or both fingers move across the screen

• One or both fingers lift off the device

• A series of quick taps, such as ...