Animation stops when using UINavigationController or UITabView - iphone

Question

I have a strange bug that I can't seem to figure out. I'm creating a little shining animation, which works perfectly, but for some reason stops when I navigate to another view via UINavigationController or UITabView (strangely modal view's don't affect it). Any ideas why, and how I can make sure the animation doesn't stop?
UIView *whiteView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
[whiteView setBackgroundColor:[UIColor whiteColor]];
[whiteView setUserInteractionEnabled:NO];
[self.view addSubview:whiteView];
CALayer *maskLayer = [CALayer layer];
maskLayer.backgroundColor = [[UIColor colorWithRed:1.0f green:1.0f blue:1.0f alpha:0.0f] CGColor];
maskLayer.contents = (id)[[UIImage imageNamed:#"ShineMask.png"] CGImage];
// Center the mask image on twice the width of the text layer, so it starts to the left
// of the text layer and moves to its right when we translate it by width.
maskLayer.contentsGravity = kCAGravityCenter;
maskLayer.frame = CGRectMake(-whiteView.frame.size.width,
0.0f,
whiteView.frame.size.width * 2,
whiteView.frame.size.height);
// Animate the mask layer's horizontal position
CABasicAnimation *maskAnim = [CABasicAnimation animationWithKeyPath:#"position.x"];
maskAnim.byValue = [NSNumber numberWithFloat:self.view.frame.size.width * 9];
maskAnim.repeatCount = HUGE_VALF;
maskAnim.duration = 3.0f;
[maskLayer addAnimation:maskAnim forKey:#"shineAnim"];
whiteView.layer.mask = maskLayer;

Answer 1

Your maskAnim is retained by maskLayer, which is retained by whiteView's layer, which is retained by whiteView, which is retained by self.view. So this entire object graph will live until your view controller's view gets dealloc'd.
When you navigate away from your view controller, UIKit unloads your view to free up memory. When the view gets dealloc'd, so does your maskAnim. When you navigate back to your view controller, UIKit reconstructs your view hierarchy, either by reloading it from its .xib, or by calling loadView, depending on which technique you used.
So you need to make sure that the code you used to set up your maskAnim gets called again after UIKit reconstructs your view hierarchy. There are four methods you might consider: loadView, viewDidLoad, viewWillAppear:, and viewDidAppear:.
loadView is a sensible option if you use that method to build your view hierarchy (as opposed to loading it from a .xib), but you'll have to change your code so that it doesn't depend on the self.view property, which would trigger loadView recursively. viewDidLoad is also a good choice. With either of these options you you need to be careful because UIKit might resize your view after viewDidLoad if it wasn't constructed at the right size. This could cause bugs since your code depends on self.view.frame.size.width.
If you set up your animation in viewWillAppear: or viewDidAppear:, you can be sure that your view's frame will be the proper dimension, but you need to be careful with these methods because they can get called more than once after the view gets loaded, and you don't want to add your whiteView subview more than once.
What I'd probably do is make whiteView a retained property, and lazy load it in viewWillAppear: like this:
- (UIView *)setupWhiteViewAnimation {
// Execute your code above to setup the whiteView without adding it
return whiteView;
}
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
if (!self.whiteView) {
self.whiteView = [self setupWhiteViewAnimation];
[self.view addSubview:self.whiteView];
}
}
- (void)viewDidUnload {
self.whiteView = nil; // Releases your whiteView when the view is unloaded
[super viewDidUnload];
}
- (void)dealloc {
self.whiteView = nil; // Releases your whiteView when the controller is dealloc'd
[super dealloc];
}