23Controlling Animation with CAAnimation
An animation object drives change over time. An animation object is an instruction set (“move from point A to point B over 2 seconds”) that can be added to a CALayer instance. When an animation object is added to a layer, that layer begins following the instructions of the animation. Many properties of CALayer can be animated by animation objects: opacity, position, transform, bounds, and contents are just a few.
While you have not yet used animations objects explicitly, all animation in iOS is driven by them, including the animations you saw in the last chapter. The abstract superclass for all animation objects is CAAnimation. CAAnimation is responsible for handling timing; for instance, ...