The DefMDIChildProc function provides default processing for any window message that the window procedure of a multiple document interface (MDI) child window does not process. A window message not processed by the window procedure must be passed to the DefMDIChildProc function, not to the DefWindowProc function.
LRESULT DefMDIChildProc(
HWND hWnd, // handle to MDI child 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.
The DefMDIChildProc function assumes that the parent window of the MDI child window identified by the hWnd parameter was created with the MDICLIENT class.
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 DefMDIChildProc instead. In addition, DefMDIChildProc also handles the following messages:
| Message | Response |
|---|---|
| WM_CHILDACTIVATE | Performs activation processing when MDI child windows are sized, moved, or displayed. This message must be passed. |
| WM_GETMINMAXINFO | Calculates the size of a maximized MDI child window, based on the current size of the MDI client window. |
| WM_MENUCHAR | Passes the message to the MDI frame window. |
| WM_MOVE | Recalculates MDI client scroll bars if they are present. |
| WM_SETFOCUS | Activates the child window if it is not the active MDI child window. |
| WM_SIZE | Performs operations necessary for changing the size of a window, especially for maximizing or restoring an MDI child window. Failing to pass this message to the DefMDIChildProc function produces highly undesirable results. |
| WM_SYSCOMMAND | Handles window menu commands: SC_NEXTWINDOW, SC_PREVWINDOW, SC_MOVE, SC_SIZE, and SC_MAXIMIZE. |
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, DefFrameProc, DefWindowProc, WM_CHILDACTIVATE, WM_GETMINMAXINFO, WM_MENUCHAR, WM_MOVE, WM_SETFOCUS, WM_SETTEXT, WM_SIZE, WM_SYSCOMMAND