Swift3 Xcode8 Ios10 開發筆記

設置不同subView的層次：

//將subView挪到最上邊  
self.view.bringSubviewToFront(subView)  
  
//將subView挪到最下邊  
self.view.sendSubviewToBack(subView)  
  
//互換  
self.view.exchangeSubviewAtIndex(2, withSubviewAtIndex: 3)