暂停/继续 动画

//暂停layer上面的动画

- (void)pauseLayer:(CALayer*)layer

{

    CFTimeInterval pausedTime = [layer convertTime:CACurrentMediaTime() fromLayer:nil];

    layer.speed = 0.0;

    layer.timeOffset = pausedTime;

}

//继续layer上面的动画

- (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;

}