iOS图层动画突然停止

Question

我正在尝试使用此库中的动画： https://github.com/shu223/PulsingHalo

我有一个UIScrollView，其中有一个宽度更大的UIImageView

    UIScrollView *scrollView;
    scrollView  = [[UIScrollView alloc] init];
    scrollView.showsHorizontalScrollIndicator = NO;
    scrollView.showsVerticalScrollIndicator = NO;

    scrollView.delegate = self;
    self.scrollView = scrollView;
    [self.view insertSubview:scrollView belowSubview:self.optionsButton];
    scrollView.translatesAutoresizingMaskIntoConstraints  = NO;

    imageView = [[UIImageView alloc] init];
    self.mapImageView = imageView;
    UIImage* mapImg = [UIImage imageNamed:@"..."];
    // Add image (larger than screen size) to the image view.
    [imageView setImage: mapImg];

// Set the constraints for the scroll view and the image view.
    NSDictionary* viewsDictionary = NSDictionaryOfVariableBindings(scrollView, imageView);
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[scrollView]|" options:0 metrics: 0 views:viewsDictionary]];
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[scrollView]|" options:0 metrics: 0 views:viewsDictionary]];
    [scrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[imageView]|" options:0 metrics: 0 views:viewsDictionary]];
    [scrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[imageView]|" options:0 metrics: 0 views:viewsDictionary]];

在此之后，我以编程方式向我的scrollview添加了一堆按钮。例如：

UIButton* flagButton = [UIButton new];
[self.scrollView addSubview: flagButton];
flagButton.translatesAutoresizingMaskIntoConstraints = NO;
NSLayoutConstraint* xc = [NSLayoutConstraint constraintWithItem:flagButton attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.mapImageView attribute:NSLayoutAttributeLeft multiplier:1.f constant:x];
NSLayoutConstraint* yc = [NSLayoutConstraint constraintWithItem:flagButton attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.mapImageView attribute:NSLayoutAttributeTop multiplier:1.f constant:y];
[self.view addConstraints@[xc, yc]];

现在我想为这个按钮创建光环。我为它创建了一个特定的视图，以我的按钮为中心。我仍然没有完全围绕定位，所以我现在暂时没有定位。

UIView* haloView = [UIView new];
haloView.backgroundColor = [UIColor clearColor];
NSLayoutConstraint* constraintHeight = [NSLayoutConstraint constraintWithItem:haloView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:flagButton attribute:NSLayoutAttributeHeight multiplier:2.0 constant:0.f];
NSLayoutConstraint* constraintWidth = [NSLayoutConstraint constraintWithItem:haloView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:flagButton attribute:NSLayoutAttributeWidth multiplier:2.0 constant:0.f];
NSLayoutConstraint* constraintCenterX = [NSLayoutConstraint constraintWithItem:haloView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:flagButton attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.f];
NSLayoutConstraint* constraintCenterY = [NSLayoutConstraint constraintWithItem:haloView attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:flagButton attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.f];
[self.view insertSubview:haloView belowSubview:flagButton];
haloView.translatesAutoresizingMaskIntoConstraints = NO;
constraintCenterX.active = YES;
constraintCenterY.active = YES;
constraintHeight.active = YES;
constraintWidth.active = YES;
PulsingHaloLayer *halo = [PulsingHaloLayer layer];
[haloView.layer insertSublayer:halo atIndex:0];
halo.radius = 50.0;
halo.haloLayerNumber = 4;
halo.duration = 4.0;

这通常应该为我提供链接库中显示的脉冲动画。而且我确实得到了它。这种行为很难描述，但它似乎正确启动，然后在它应该循环时突然停止，然后在一秒后再次重启。基本上，它似乎没有正确循环，我不知道为什么。

这是视图层次结构。最后一个“UIView”是具有Halo层的那个。

这些是UIView的属性，如调试器所示。

这些是UIScrollView的属性。

感谢您的帮助。