CAAnimationGroup的最大持续时间值(CFTimeInterval)是多少？

Question

我有两个旋转动画CAAnimationGroup,一个从零开始,另一个重复并从该状态自动反转:

- (void)addWobbleAnimationToView:(UIView *)view amount:(float)amount speed:(float)speed
{
    NSMutableArray *anims = [NSMutableArray array];

    // initial wobble
    CABasicAnimation *startWobble = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
    startWobble.toValue = [NSNumber numberWithFloat:-amount];
    startWobble.duration = speed/2.0;
    startWobble.beginTime = 0;
    startWobble.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
    [anims addObject:startWobble];

    // rest of wobble
    CABasicAnimation *wobbleAnim = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
    wobbleAnim.fromValue = [NSNumber numberWithFloat:-amount];
    wobbleAnim.toValue = [NSNumber numberWithFloat:amount];
    wobbleAnim.duration = speed;
    wobbleAnim.beginTime = speed/2.0;
    wobbleAnim.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
    wobbleAnim.autoreverses = YES;
    wobbleAnim.repeatCount = INFINITY;
    [anims addObject:wobbleAnim];

    CAAnimationGroup *wobbleGroup = [CAAnimationGroup animation];
    wobbleGroup.duration = DBL_MAX; // this stops it from working
    wobbleGroup.animations = anims;

    [view.layer addAnimation:wobbleGroup forKey:@"wobble"];
}

由于CFTimeInterval被定义为double,我尝试将动画组的持续时间设置为DBL_MAX,但这会阻止动画组运行.但是,如果我将它设置为一个大数字,如10000,它运行正常.我可以在a的持续时间内使用的最大数字是多少CAAnimationGroup,以确保它尽可能接近无穷大？

更新:似乎如果我输入一个非常大的值,DBL_MAX / 4.0然后它冻结一秒钟,然后开始动画.如果我输入值,DBL_MAX / 20.0则开头的冻结要小得多.似乎在持续时间内具有如此大的值会导致它冻结.除了在持续时间内使用非常大的值之外,还有更好的方法吗？

Answer 1

我现在面临着完全相同的问题...我希望有人证明我错了，但我认为处理这种情况的唯一合理方法是将第一个动画移动到 a CATransaction，并使用以下方法将其与自动反转动画链接起来：

[CATransaction setCompletionBlock:block];

这并不理想，但完成了工作。

关于您关于从后台返回时动画暂停的问题，这是 CoreAnimation 框架的一个经典限制，已经为此提出了许多解决方案。我解决这个问题的方法是简单地在动画的随机点重置动画，通过随机化属性timeOffset。用户无法准确判断动画状态应该是什么，因为应用程序位于后台。这是一些可以提供帮助的代码（查找评论//RANDOMIZE!!）：

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(startAnimating)
                                             name:UIApplicationWillEnterForegroundNotification
                                           object:[UIApplication sharedApplication]];

...

for (CALayer* layer in _layers) 
{
    // RANDOMIZE!!!
    int index = arc4random()%[levels count];
    int level = ...;
    CGFloat xOffset = ...;

    layer.position = CGPointMake(xOffset, self.bounds.size.height/5.0f + yOffset * level);

    CGFloat speed = (1.5f + (arc4random() % 40)/10.f);
    CGFloat duration = (int)((self.bounds.size.width - xOffset)/speed);

    NSString* keyPath = @"position.x";
    CABasicAnimation* anim = [CABasicAnimation animationWithKeyPath:keyPath];

    anim.fromValue      = @(xOffset);
    anim.toValue        = @(self.bounds.size.width);
    anim.duration       = duration;
    anim.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
    // RANDOMIZE!!
    anim.timeOffset     = arc4random() % (int) duration;
    anim.repeatCount    = INFINITY;

    [layer removeAnimationForKey:keyPath];
    [layer addAnimation:anim forKey:keyPath];
    [_animatingLayers addObject:layer];
}