UIScrollView一次只能向一个方向滚动

I have a UIScrollView and I want it to be able to scroll in both directions (it currently does) but only one at a time. So, for instance, if you start scrolling it horizontally, it won't move vertically at all until you let go and start moving it vertically. How could I go about doing this?I have a UIScrollView and I want it to be able