setLayout: Attempting to set QLayout "" on MainWindow "MainWindow", which already has a layout

 如题，出现这个的原因是，如果你的窗口继承的是QMainwindow，需要设置

setCentralWidget（）;
如下：
 

   
   
   
   

    
    
    
    
 
     
 
      QWidget 
      * widget 
      = 
      new 
      QWidget 
      ( mainWindow 
      ) ; 
     
 
    
    
    
    
 
     

       widget 
      - >setLayout 
      ( yourMainLayout 
      ) ; 
     
 
    
    
    
    
 
     

       mainWindow 
      - >setCentralWidget 
      (widget 
      ) ; 
     
 
   
   
   
   
设置好一个widget,将其加入到CentralWidget即可.