The DefFrameProc function provides default processing for any window messages that the window procedure of a multiple document interface (MDI) frame window does not process. All window messages that are not explicitly processed by the window procedure must be passed to the DefFrameProc function, not the DefWindowProc function.
LRESULT DefFrameProc(
HWND hWnd, // handle to MDI frame window
HWND hWndMDIClient, // handle to MDI client window
UINT uMsg, // message
WPARAM wParam, // first message parameter
LPARAM lParam // second message parameter
);
The return value specifies the result of the message processing and depends on the message. If the hWndMDIClient parameter is NULL, the return value is the same as for the DefWindowProc function.
When an application's window procedure does not handle a message, it typically passes the message to the DefWindowProc function to process the message. MDI applications use the DefFrameProc and DefMDIChildProc functions instead of DefWindowProc to provide default message processing. All messages that an application would usually pass to DefWindowProc (such as nonclient messages and the WM_SETTEXT message) should be passed to DefFrameProc instead. The DefFrameProc function also handles the following messages:
| Message | Response |
|---|---|
| WM_COMMAND | Activates the MDI child window that the user chooses. This message is sent when the user chooses an MDI child window from the Window menu of the MDI frame window. The window identifier accompanying this message identifies the MDI child window to be activated. |
| WM_MENUCHAR | Opens the window menu of the active MDI child window when the user presses the alt+ – (minus) key combination. |
| WM_SETFOCUS | Passes the keyboard focus to the MDI client window, which in turn passes it to the active MDI child window. |
| WM_SIZE | Resizes the MDI client window to fit in the new frame window's client area. If the frame window procedure sizes the MDI client window to a different size, it should not pass the message to the DefWindowProc function. |
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Unsupported.
Header: Declared in winuser.h.
Import Library: Use user32.lib.
Unicode: Implemented as Unicode and ANSI versions on Windows NT.
Multiple Document Interface Overview, Multiple Document Interface Functions, DefMDIChildProc, DefWindowProc, WM_SETTEXT