Everyone and every book claims that there are implicit animations happening in CALayer. However, every time I wanted to verify that so far, I end up with a hard-snap to the set value. No animation at all.
Here's an example in a project where nothing else is happening. All I do is create a view, then get it's CALayer instance and do something that should be implicitly animated.
[theLayer setValue:[NSNumber numberWithFloat:M_PI * 1.1] forKeyPath:@"transform.rotation.z"];
Another one:
CGRect currentBounds = theLayer.bounds;
currentBounds.size.width += 120.f;
[self.animatedLayer setBounds:currentBounds];
The view contains some stuff of course so I can see the change. I see the visual change, but as a hard snap. No animation at all.
So either all those books are wrong and have old Mac OS X knowledge in mind when writing about Core Animation and implicit animations, or I'm doing something wrong. Can anyone provide an working example that demonstrates implicit animations on the iPhone?
UIKit disables implicit animations. To be more specific, a CALayer associated with a UIView will never implicitly animate. CALayers that you create yourself and that are not associated with a UIView will buy into the normal implicit animation machinery.
If you're interested in how this works, implicit animations happen after the normal -actionForKey: lookup. If there's a CAAction for a given property, it's used. Otherwise, the implicit animation is used. In the case of a CALayer associated with a UIView, UIView implements the -actionForLayer:forKey: delegate method, and when not in a UIView animation block it always returns [NSNull null] to signify that the action lookup should stop here. This prevents implicit animations from working. Inside of a UIView animation block, it constructs its own action to represent the current UIView animation settings. Again, this prevents implicit animations.
If you need to animate CALayer properties that UIView won't do for you, you can use an explicit CAAnimation subclass (such as CABasicAnimation).