如果你'在代码中重新设置视图，将超级视图的 clipsToBounds 属性设置为 YES 。

If you're setting up your views in code, set the clipsToBounds property of the superview to YES.

如果您要在笔尖中设置视图，请在超级视图上选中 on 剪辑子视图复选框。它默认是关闭的，如截图所示：

If you're setting up your views in a nib, turn on the "Clip Subviews" checkbox on the superview. It's off by default, as in this screenshot: