CoreAnimation暂停和继续Layer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;  }