The Core iOS Developer’s Cookbook, Fifth Edition

Recipe: Adding Gestures to Layout

Recipe 10-7 builds on Recipe 10-6, adding interactive gestures that adjust presentation layout. It uses two recognizers, a pinch recognizer and a rotation recognizer, to enable users to scale and rotate the circle of views. These items are set up to recognize simultaneously, so users can pinch and rotate at the same time.

The rotate recognizer uses a slightly more sophisticated approach than the pinch one. Unlike pinch values, rotations are relative. You rotate by an amount, not to a specific angle. To accommodate this, Recipe 10-7 implements callbacks to handle two states. The first is called as rotations happen, updating the presentation to match each movement. The second resets the rotation baseline as the ...