KVO on a views geometry

gistfile1.txt

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 300, 200)];
    view.backgroundColor = [UIColor blueColor];
    [self.view addSubview:view];
    
    [view addObserver:self forKeyPath:@"frame" options:0 context:NULL];
    [view.layer addObserver:self forKeyPath:@"bounds" options:0 context:NULL];
    [view.layer addObserver:self forKeyPath:@"transform" options:0 context:NULL];
    [view.layer addObserver:self forKeyPath:@"position" options:0 context:NULL];
    [view.layer addObserver:self forKeyPath:@"zPosition" options:0 context:NULL];
    [view.layer addObserver:self forKeyPath:@"anchorPoint" options:0 context:NULL];
    [view.layer addObserver:self forKeyPath:@"anchorPointZ" options:0 context:NULL];
    [view.layer addObserver:self forKeyPath:@"frame" options:0 context:NULL];
    [view.layer addObserver:self forKeyPath:@"transform" options:0 context:NULL];
    
    [self doSomeRandomAlterationToViewRepeated:view];
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    NSLog(@"View changed its geometry");
}

- (void)doSomeRandomAlterationToViewRepeated:(UIView *)view
{
    double delayInSeconds = 0.5;
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
        [self doSomeRandomAlterationToView:view];
        [self doSomeRandomAlterationToViewRepeated:view];
    });
}

- (void)doSomeRandomAlterationToView:(UIView *)view
{
    switch (arc4random_uniform(9)) {
        case 0:
        {
            NSLog(@"Changing frame");
            CGRect frame = view.frame;
            frame.size.width += (float)arc4random_uniform(100);
            view.frame = frame;
        }
            break;
        case 1:
        {
            NSLog(@"Changing bounds");
            CGRect bounds = view.bounds;
            bounds.size.width = (float)arc4random_uniform(100);
            view.frame = bounds;
        }
            break;
        case 2:
        {
            NSLog(@"Changing center");
            CGPoint center = view.center;
            center.x = (float)arc4random_uniform(100);
            view.center = center;
        }
            break;
        case 3:
        {
            NSLog(@"Changing layer.anchorPoint");
            CGPoint anchor = view.layer.anchorPoint;
            anchor.x = ((float)arc4random_uniform(5) / 10.0);
            view.layer.anchorPoint = anchor;
        }
            break;
        case 4:
        {
            NSLog(@"Changing layer.position");
            CGPoint position = view.layer.position;
            position.x = ((float)arc4random_uniform(5) / 10.0);
            view.layer.position = position;
        }
            break;
        case 5:
        {
            NSLog(@"Changing layer.anchorPointZ");
            CGFloat anchor = view.layer.anchorPointZ;
            anchor = (float)arc4random_uniform(20);
            view.layer.anchorPointZ = anchor;
        }
            break;
        case 6:
        {
            NSLog(@"Changing layer.bounds");
            CGRect bounds = view.layer.bounds;
            bounds.size.width = (float)arc4random_uniform(100);
            view.layer.bounds = bounds;
        }
            break;
        case 7:
        {
            NSLog(@"Changing layer.transform");
            CATransform3D transform = view.layer.transform;
            transform.m32 = (float)arc4random_uniform(100);
            view.layer.transform = transform;
        }
            break;
        case 8:
        {
            NSLog(@"Changing transform");
            CGAffineTransform transform = view.transform;
            transform.a = ((float)arc4random_uniform(5) / 10.0);
            view.transform = transform;
        }
            break;
            
        default:
            
            break;
    }
}

Why [view.layer addObserver:self forKeyPath:@"zPosition" options:0 context:NULL]; exists twice?

@pedro380085 typo :) (fixed now)

See http://stackoverflow.com/questions/4874288/use-key-value-observing-to-get-a-kvo-callback-on-a-uiviews-frame

It is unexpected behaviour. Sometimes it does not work