从AFX_MANAGE_STATE(AfxGetStaticModuleState())说起
AFX_MANAGE_STATE(AfxGetStaticModuleState())的作用：用于模块切换时的状态保护，
1.AfxGetStaticModuleState()指向当前模块状态;
2.当前函数调用结束后原模块的状态自动被恢复；
3.用于DLL中所调用MFC函数、类、资源时的模块状态切换;
[MSDN]
By default, MFC uses the resource handle of the main application to load the resource template. If you have an exported function in a DLL, such as one that launches a dialog box in the DLL, this template is actually stored in the DLL module. You need to switch the module state for the correct handle to be used. You can do this by adding the following code to the beginning of the function:
AFX_MANAGE_STATE(AfxGetStaticModuleState( ));
This swaps the current module state with the state returned from AfxGetStaticModuleState until the end of the current scope
也就是说，并不是每一个dll的输出函数前都要调用它，只有在要输出对话框等用到资源时才要调用！
dll中资源是共享的，用这个函数的目的是防止不同的进程修改资源从而产生错误!
缺省情况下MFC使用主应用程序的资源句柄来载入资源模板，而DLL中的资源模板是存在于DLL模板中，
因此要使用这一语句切换到 DLL 。