说明：  1、一个 MFC 的多文档（MDI）应用。在父窗口中，我如何检查所有的MDI子窗口是否都已经关闭？如果都关闭了，那么我想在我的主窗口激活一个窗格。2、用 Visual Studio .NET 和 MFC 做一个程序。在程序里，用户要选择一个文件夹，并在其中拷贝文件。我可以调用 OpenFileDialog 让用户选择某个文件，但如何让打开对话框只显示文件夹呢？我见过好多安装程序给出的对话框里只显示文件夹，但我好像找不到这样的标志。
(1, a MFC multi-document (MDI) applications. In the parent window, how do I check all the MDI child window is already closed? If you were closed, then I think in my main window to activate a pane. 2, with Visual Studio. NET and MFC to do a procedure. In the process, the user must select a folder and copy files in one. I can call the OpenFileDialog to allow the user to choose a file, but how to open the dialog box only shows folders then? I have seen a lot of the installation procedure given in the dialog box shows only folders, but I seem to find such signs.)