Swift3 Xcode8 Ios10 开发笔记

设置不同subView的层次：

//将subView挪到最上边  
self.view.bringSubviewToFront(subView)  
  
//将subView挪到最下边  
self.view.sendSubviewToBack(subView)  
  
//互换  
self.view.exchangeSubviewAtIndex(2, withSubviewAtIndex: 3)