有没有办法暂停核心动画并在以后的某个时间恢复它？

I have several Core Animation's going on at the same time. They all have an context and an animation id, where the context is the object that's beeing animated (UIImageView objects). I would like to pause them, so that the animation just stops temporarily, and then when some things are done, resume it to complete it. These things happen only on very fast scroll movements in an UIScrollView. I want to improve performance by stopping all ongoing animations but not the one that makes the scroll view scroll. I have implemented an custom animation of the contentOffset for that scroll view.I have several Core Animation's going on at the