Fade continuously between two CAGradientLayer color set-ups?

I want a UIButton to pulse, and I plan to do this by fadin开发者_如何学编程g slowly between two color arrays on a CAGradientLayer. Is there a way to repeat an animation back and forth?

Yes. In Core Animation you create an explicit animation to do the fade and then you must also set two other properties for the animation object: autoReverses and repeatCount (number of repetitions to perform, each 2 repetitions will take you through your animation and back again). In your case you’d add the following lines to your code that sets up the animation object (I’ll call the object anim):

 anim.repeatCount = HUGE_VALF;
 anim.autoReverses = YES;

HUGE_VALF causes the animation to repeat forever though you could specify a number larger than any amount of repetitions that might occur.

These properties aren’t shown in the documentation of the CAAnimation object or it’s subclasses since it is defined in the CAMediaTiming Protocol which is adopted by CAAnimation and it's subclasses. But you can see examples and discussion of the CAMediaTiming protocol as it applies to CAAnimation objects in the Timing, Timespaces, and CAAnimation section of the Animation Types and Timing Programming Guide either on Apple’s Developer site or in the documentation provided through XCode.

(Many people seem to find Apple's Core Animation documentation to be particularly hard to understand until you get a good overall grasp of the disparate parts. I basically knew what you had to do but still found it hard to remember exactly where to find the actual information as to the properties involved.)