UIView（不带控制器）：自我消失时得到通知

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.