iOS Core Animation fails after segue / view transition - ios5

Question

I have a basic animation, simply rotating an image, I'm using Core Animation. In the viewWillAppear method I create the animation:
gearRotate = [CABasicAnimation animationWithKeyPath:#"transform.rotation"];
gearRotate.repeatCount = HUGE_VALF;
gearRotate.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
gearRotate.duration = 2;
gearRotate.fromValue = 0;
gearRotate.toValue = [NSNumber numberWithFloat:(360*M_PI)/180];
[gearButton.imageView.layer addAnimation:gearRotate forKey:#"transform.rotation"];
[self stopGear];
I'm calling stopGear initially to pause the animation. I did have this code in viewDidLoad to start with. Anyway, when the animation is called it works fine:
-(void)startGear {
CFTimeInterval pausedTime = [gearButton.imageView.layer timeOffset];
gearButton.imageView.layer.speed = 1.0;
gearButton.imageView.layer.timeOffset = 0.0;
gearButton.imageView.layer.beginTime = 0.0;
CFTimeInterval timeSincePause = [gearButton.imageView.layer convertTime:CACurrentMediaTime() fromLayer:nil] - pausedTime;
gearButton.imageView.layer.beginTime = timeSincePause;
}
And this pause method works fine too:
-(void)stopGear {
CFTimeInterval pausedTime = [gearButton.imageView.layer convertTime:CACurrentMediaTime() fromLayer:nil];
gearButton.imageView.layer.speed = 0.0;
gearButton.imageView.layer.timeOffset = pausedTime;
}
However, this all fails if I segue to another view then back to the main view. The app runs fine but the animation will never run if I've been to another view.
This is why I initially moved this code to viewWillAppear, thinking I needed to re-create my animation, but no beans. Any ideas?
Thanks.

Answer 1

OK, so I solved this by re-thinking how animations work. I'm now simply creating the animation each time I want it to run:
-(void)startGear {
gearRotate = [CABasicAnimation animationWithKeyPath:#"transform.rotation"];
gearRotate.repeatCount = HUGE_VALF;
gearRotate.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
gearRotate.duration = 2;
gearRotate.fromValue = 0;
gearRotate.toValue = [NSNumber numberWithFloat:(360*M_PI)/180];
[[gearButton.imageView layer] addAnimation:gearRotate forKey:#"transform.rotation"];
}
And when I want to pause it, I simply remove it:
-(void)stopGear {
[[gearButton.imageView layer] removeAnimationForKey:#"transform.rotation"];
}
I'm not sure currently if this is the Apple preferred method, but it works solidly.

Answer 2

Instead of using gearRotate.repeatCount = HUGE_VALF; you could have used the following approach in order to keep your animation running after performing a segue to another view controller:
-(void)startGear {
[[gearButton.imageView layer] removeAnimationForKey:#"transform.rotation"];
gearRotate = [CABasicAnimation animationWithKeyPath:#"transform.rotation"];
gearRotate.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
gearRotate.duration = 2;
gearRotate.fromValue = 0;
gearRotate.toValue = [NSNumber numberWithFloat:(360*M_PI)/180];
[[gearButton.imageView layer] addAnimation:gearRotate forKey:#"transform.rotation"];
[self performSelector:#selector(startGear) withObject:nil afterDelay:gearRotate.duration];
}