ios中运用core animation暂停和继续动画

animation暂停和继续动画
核心代码如下
//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;
}