Looped, reversible animation using Core Animation
cabasicanimation, cocoa-touch, core-animation, ios, ios5
Solution
Yes, you can do this, right within `CABasicAnimation`. The trick is that many of its most important methods are not in the CABasicAnimation Class Reference, or even in its superclasses. CABasicAnimation implements a protocol called `CAMediaTiming`. See the CAMediaTiming Protocol Reference.
You want to know about two properties in particular: `autoreverses` and `repeatCount`. Both are self-explanatory, but what if you want infinite repeats? From the entry for `repeatCount`:
May be fractional. If the repeatCount is 0, it is ignored. Defaults to 0. If both repeatDuration and repeatCount are specified the behavior is undefined.
Setting this property to HUGE_VALF will cause the animation to repeat forever.
Can you work it out from there?
Problem
In my iOS 5 app I have a custom `UIButton` that has a red orb as its image. When the button is tapped I would like the orb to start pulsing/fading between red and green. I have both red and green images and can successfully cross-disolve between the two using the following code: ``` CABasicAnimation *imageSwitchAnimation = [CABasicAnimation animationWithKeyPath:@"contents"]; imageSwitchAnimation.fromValue = (id)[UIImage imageNamed:@"red.png"].CGImage; imageSwitchAnimation.toValue = (id)[UIImage imageNamed:@"green.png"].CGImage; imageSwitchAnimation.duration = 1.5f; [self.button.imageView.layer addAnimation:imageSwitchAnimation forKey:@"animateContents"]; ``` However, I would like the animation to continue forever (well, until I tell it to stop) and also for the animation to reverse and loop. In other words, fade red -> green -> red and then repeat. I tried putting the animation block above into an endless loop (together with some logic to determine whether the fading should go from red -> green or green -> red) but this just locks-up the entire app. Other solutions seem to use Cocos2d, which seems fairly heavy-weight since this is the only animation I need in the app (so I don't want to use such frameworks unless absolutely needed). Any help would be greatly appreciated.