Qt开发问答
1, Difference between Dialog and widget and QMainWindow
http://www.qtcentre.org/threads/3465-Difference-between-Dialog-and-widget-and-QMainWindow
A widget is an object that can be displayed on the screen. For example a window or a button.
A dialog is a top-level widget, that is always displayed in separate window (i.e. you can‘t put it on another widget).
A main window is also a top-level widget, but it has a predefined layout that includes a menu bar, a status bar and place for tool bars and dock areas.
原文：http://www.cnblogs.com/cutepig/p/6506220.html