单文档双视图以及单文档多视图的程序。可以实现任意多的视图之间的切换，但是用户始终只看到一个视图。根据csdn上的一个源码改编，希望对大家有用。-Single document, as well as dual-view multi-view single document procedures. Can achieve many of arbitrary switching between the view, but the user has only to see a view. Accord