A main window provides a framework for building an application's user interface. Qt has QMainWindow and its related classes for main window management. QMainWindow has its own layout to which you can add QToolBars, QDockWidgets, a QMenuBar, and a QStatusBar. The layout has a center area that can be occupied by any kind of widget. You can see an image of the layout below.
Note: Creating a main window without a central widget is not supported. You must have a central widget even if it is just a placeholder.
個人覺得，如果不是爲了更方便的去添加QToolBars, QDockWidgets, a QMenuBar, and a QStatusBar ，我寧願用QWidget類。
