注册全局窗口类，看MSDN介绍：Application Global ClassesAn application global class is a window class registered by an executable or dynamic-link library (DLL) that is available to all other modules in the process. For example, your .dll can call the RegisterClassEx function to register a window class that defines a custom control as an application global class so that a process that loads the .dll can create instances of the custom control. Windows NT/Windows 2000/Windows XP: To create a class that can be used in every process, create the window class in a .dll and load the .dll in every process. To load the .dll in every process, add its name to the AppInit_DLLs value in following registry key: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\WindowsWhenever a process starts, the system loads the specified .dll in the context of the newly started process before calling its entry-point function. The .dll must register the class during its initialization procedure and must specify the CS_GLOBALCLASS style. For more information, see Class Styles. To remove an application global class and free the storage associated with it, use the UnregisterClass function.
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