Programming iOS 4

Core Animation

Core Animation is the fundamental underlying iOS animation technology. View animation and implicit layer animation are merely convenient façades for Core Animation. Core Animation is explicit layer animation, and revolves primarily around the CAAnimation class and its subclasses, which allow you to create far more elaborate specifications of an animation than anything we’ve encountered so far.

You may never program at the level of Core Animation, but you should read this section anyway, if only to learn how animation really works and to get a sense of the mighty powers you would acquire if you did elect to use Core Animation directly. In particular, Core Animation:

• Works even on a view’s underlying layer. Thus, Core Animation is the only way to apply full-on layer property animation to a view.
• Provides fine control over the intermediate values and timing of an animation.
• Allows animations to be grouped into complex combinations.
• Adds transition animation effects that aren’t available otherwise, such as new content “pushing” the previous content out of a layer.

CABasicAnimation and Its Inheritance

The simplest way to animate a property with Core Animation is with a CABasicAnimation object. CABasicAnimation derives much of its power through its inheritance, so I’m going to describe that inheritance as well as CABasicAnimation itself. You will readily see that all the property animation features we have met so far are embodied in a CABasicAnimation instance.

CAAnimation ...