Chaining animations and memory management - iphone

Question

Got a question. I have a subclassed UIView that is acting as my background where I am scrolling the ground. The code is working really nice and according to the Instrumentation, I am not leaking nor is my created and still living Object allocation growing.
I have discovered else where in my application that adding an animation to a UIImageView that is owned by my subclassed UIView seems to bump up my retain count and removing all animations when I am done drops it back down.
My question is this, when you add an animation to a layer with a key, I am assuming that if there is already a used animation in that entry position in the backing dictionary that it is released and goes into the autorelease pool?
For example:
- (void)animationDidStop:(CAAnimation *)theAnimation finished:(BOOL)flag
{
NSString *keyValue = [theAnimation valueForKey:#"name"];
if ( [keyValue isEqual:#"step1"] && flag ) {
groundImageView2.layer.position = endPos;
CABasicAnimation *position = [CABasicAnimation animationWithKeyPath:#"position"];
position.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
position.toValue = [NSValue valueWithCGPoint:midEndPos];
position.duration = (kGroundSpeed/3.8);
position.fillMode = kCAFillModeForwards;
[position setDelegate:self];
[position setRemovedOnCompletion:NO];
[position setValue:#"step2-1" forKey:#"name"];
[groundImageView2.layer addAnimation:position forKey:#"positionAnimation"];
groundImageView1.layer.position = startPos;
position = [CABasicAnimation animationWithKeyPath:#"position"];
position.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
position.toValue = [NSValue valueWithCGPoint:midStartPos];
position.duration = (kGroundSpeed/3.8);
position.fillMode = kCAFillModeForwards;
[position setDelegate:self];
[position setRemovedOnCompletion:NO];
[position setValue:#"step2-2" forKey:#"name"];
[groundImageView1.layer addAnimation:position forKey:#"positionAnimation"];
}
else if ( [keyValue isEqual:#"step2-2"] && flag ) {
groundImageView1.layer.position = midStartPos;
CABasicAnimation *position = [CABasicAnimation animationWithKeyPath:#"position"];
position.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
position.toValue = [NSValue valueWithCGPoint:endPos];
position.duration = 12;
position.fillMode = kCAFillModeForwards;
[position setDelegate:self];
[position setRemovedOnCompletion:NO];
[position setValue:#"step1" forKey:#"name"];
[groundImageView1.layer addAnimation:position forKey:#"positionAnimation"];
}
}
This chains animations infinitely, and as I said one it is running the created and living object allocation doesn't change. I am assuming everytime I add an animation the one that exists in that key position is released.
Just wondering I am correct. Also, I am relatively new to Core Animation. I tried to play around with re-using the animations but got a little impatient. Is it possible to reuse animations?
Thanks!
Bryan

Answer 1

Your assumption is difficult to verify without Apple's source code. When you call addAnimation:forKey:, the CALayer makes a copy of the animation object. There is no guarantee from the API (in the docs or elsewhere) that it will release a running animation when another is added for the same key. It would be much safer for you to explicitly call removeAnimation:forKey: rather than relying on the API to do what you want.
Also, why have you set removedOnCompletion to NO in the code above? The default behavior of a CAAnimation is to remove itself from the layer once it has completed, and then call animationDidStop:finished: on the delegate. You can then add any other animation to the layer with the same key. Isn't this exactly what you're trying to do? It seems like you might be over thinking it a little.
As for your question about reusing animations: since the animation object is copied when added to a CALayer, you can hold a reference to an animation object that you create and keep adding it to as many layers as you want as many times as you like.