在许多软件中可以看到许多拖动的窗口，用户可以将其拖动到任何位置，也可以停靠在窗口的一边，本例子就实现了该功能。供初学者学习 -In many software can be seen in many drag a window, the user can drag it to any location can also be docked at the side of the window, the example of the realization of the feature. For