Chapter 14. Recognizing Gestures


  • How to use the six gesture recognizers to recognize commonly used gestures

  • 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. The iPhone recognizes various multi-touch sequences, known as gestures, and performs the appropriate action associated with each.

In this chapter, you learn how to recognize gestures 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, your application enables users to rearrange the locations of the onscreen images, as well as change the size of the images using the pinching gesture.

Recognizing Gestures

Beginning with version 3.2 of the iPhone SDK, Apple introduced a new set of classes known as gesture recognizers. Gesture recognizers enable you to easily detect gestures performed by the user. For example, the user may use two fingers to pinch the screen, indicating an intention to zoom in and out of an image. Instead of writing ...

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