UIView (without controller) : get notified when self disappears - ios

Question

I have a UIView without any associated UIViewController constantly animating with auto layout and layoutIfNeeded (see code bellow).
But when this view (which is contained in another view) disappears (for example when a modal view covers the view it is contained in) and after I dismiss this modal view, the animating view isn't animating anymore.
I managed to animate it back with the didMoveToWindow:animated method but i'm not sure this is the proper approach.
#interface AnimatingView()
#property (strong, nonatomic) UIView *aSubview;
#property (strong, nonatomic) NSLayoutConstraint *constraintTop;
#property (assign, nonatomic, getter = isStarted) BOOL started;
#property (assign, nonatomic) BOOL stopAnimation;
#end
#implementation AnimatingView
- (id)init
{
self = [super init];
if (self) {
self.stopAnimation = YES;
/* setting base auto layout constraints */
}
return self;
}
-(void)animate{
float aNewConstant = arc4random_uniform(self.frame.size.height);
[UIView animateWithDuration:ANIMATION_DURATION animations:^{
[self removeConstraint:self.constraintTop];
self.constraintTop = [NSLayoutConstraint constraintWithItem:self.aSubview attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeTop multiplier:1 constant:aNewConstant];
[self addConstraint:self.constraintTop];
[self layoutIfNeeded];
} completion:^(BOOL finished) {
if (finished && !self.stopAnimation) {
[self animate];
}
}];
}
- (void)didMoveToWindow{
[super didMoveToWindow];
if ([self isStarted]) {
[self stop];
[self start];
}
}
-(void)start{
if (![self isStarted]) {
self.stopAnimation = NO;
[self setStarted:YES];
[self animate];
}
}
-(void)stop{
if ([self isStarted]) {
self.stopAnimation = YES;
[self setStarted:NO];
}
}
#end

Answer 1

You can always use a behavioral pattern : KVO to control the state of the UIView or what I would do, use a notification to animate the view when you want to. Both options are valid. You can have as well a delegate associated with this class and implement the behavior you want in your UIView.

Answer 2

Assuming your view is contained in another view which is contained in a Controller, you can set a BOOL variable called didReturnFromModalChildView which you set it true every time you present that modal view. When you dismiss that modal view, your application will call -(void)viewWillAppear:(BOOL)animated. Here you have to check if that BOOL variable is set to Yes and then use a public method calling if you have a reference to the view you want to animate, or a delegation process or observer-notification pattern. Don't forget to set didReturnFromModalChildView to false.
I hope this will help you.