暂停、恢复CALayer 动画

CALayer都是实现了CAMediaTiming协议（或者叫做接口）。所以layer的动画有一个很有意思的属性speed。如果一个layer的动画速度变成0.0的时候，很显然这个动画就不再动了。设置layer的speed为0时，layer的动画暂停。speed属性设置为任意大于0的值时，动画回复。

要暂停一个动画时：

-(void)pauseLayer:(CALayer*)layer {
   CFTimeInterval pausedTime = [layer convertTime:CACurrentMediaTime() fromLayer:nil];
   layer.speed = 0.0;
   layer.timeOffset = pausedTime;
}

恢复一个动画：

-(void)resumeLayer:(CALayer*)layer {
   CFTimeInterval pausedTime = [layer timeOffset];
   layer.speed = 1.0;
   layer.timeOffset = 0.0;
   layer.beginTime = 0.0;
   CFTimeInterval timeSincePause = [layer convertTime:CACurrentMediaTime() fromLayer:nil] - pausedTime;
   layer.beginTime = timeSincePause;
}

比如你有这么一个在ImageView上执行的动画，你想让这个动画开始执行后点击按钮暂停，在点击按钮恢复就可以这样：

CABasicAnimation *sizeAnim = [CABasicAnimation animationWithKeyPath:@"transform"];
        sizeAnim.fromValue = [NSValue valueWithCATransform3D:CATransform3DIdentity];
        sizeAnim.toValue = [NSValue valueWithCATransform3D:CATransform3DMakeScale(1.5f, 1.5f, 1.f)];
        sizeAnim.duration = .2f;
        sizeAnim.fillMode = kCAFillModeForwards;
        sizeAnim.removedOnCompletion = YES;
        sizeAnim.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
        [self.collectionImageView.layer addAnimation:sizeAnim forKey:@"size"];
        
        CAKeyframeAnimation *shakeAnim = [CAKeyframeAnimation animationWithKeyPath:@"transform.rotation.z"];
        shakeAnim.values = @[@(M_PI/6), @(-M_PI/6),@(M_PI/6)/*, @(-M_PI/6)*/];
        shakeAnim.timingFunctions = @[[self getTiming:kCAMediaTimingFunctionLinear]
                                      , [self getTiming:kCAMediaTimingFunctionLinear]
                                      ,[self getTiming:kCAMediaTimingFunctionLinear]];
        shakeAnim.duration = .2f;
//        shakeAnim.beginTime = CACurrentMediaTime() + sizeAnim.duration;
        [self.collectionImageView.layer addAnimation:shakeAnim forKey:@"shake"];

上面说的ImageView可以通过self.collectionImageView来访问。这里设置的执行时间都不是很长，在实验的时候最好把动画的执行时间设置的长点。

暂停&恢复的代码：

static BOOL animationStoped = NO;
- (IBAction)animationAction:(id)sender {
    if (!animationStoped) {
        [self pauseLayer:self.collectionImageView.layer];
//        animationStoped = YES;
    }
    else{
        [self resumeLayer:self.collectionImageView.layer];
    }
    animationStoped = !animationStoped;
}