MDI 应用程序是另一类重要的文档视结构程序。它的特点是：用户一次可以打开多个文档，每个文档对应不同的窗口；主窗口的菜单会自动随着当前活动的子窗口的变化而变化；可以对子窗口进行层叠、平铺等各种操作；子窗口可以在MDI 主窗口区域内定位、改变大小、最大化和最小化，当最大化子窗口时，它将占满MDI 主窗口的全部客户区。MDI 不仅可以在同一时间内同时打开多个文档，还可以为同一文档打开多个视图。在Windows 菜单下选择New ，就为当前活动文档打开一个新的子窗口。

-MDI application is another important document, as the structure of the procedure. It is characterized by: a user can open multiple documents, each document corresponds to a different window　main window menu automatically with the current activities of the sub-window changes　can be stacked pair window, tile, etc. types of operation　MDI child window in the main window positioning the region to change the size, to maximize and minimize, maximize the child window when it will occupy the entire main window MDI client area. MDI at the same time not only to open multiple documents at the same time, can also open multiple views of the same document. In the Windows menu select New, on the activities for the current document open a new sub-window.