说明：  pb提供了可在MDI窗口中显示图片及各种内容的一种方法，它既不需要API调用也不需要定制MDI窗口，它仅仅使用PB的一般编程技巧，你很容易就会弄明白它的原理:它不过是一个比较特殊的Sheet而已！它特殊在什么地方呢，还是你自己去看吧!
(pb in the MDI window display pictures and the contents of a method, it does not need an API call does not need to customize MDI windows, it is only the general use of PB programming skills, you can easily find out the principle : it is a rather exceptional Sheet! Its special in any place, or look at your own!)