DefFrameProcA function (winuser.h)

Article
02/09/2023

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.

Syntax

LRESULT DefFrameProcA(
  [in] HWND   hWnd,
  [in] HWND   hWndMDIClient,
  [in] UINT   uMsg,
  [in] WPARAM wParam,
  [in] LPARAM lParam
);

Parameters

[in] hWnd

Type: HWND

A handle to the MDI frame window.

[in] hWndMDIClient

Type: HWND

A handle to the MDI client window.

[in] uMsg

Type: UINT

The message to be processed.

[in] wParam

Type: WPARAM

Additional message-specific information.

[in] lParam

Type: LPARAM

Additional message-specific information.

Return value

Type: LRESULT

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.

Remarks

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.

Note

The winuser.h header defines DefFrameProc as an alias which automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	winuser.h (include Windows.h)
Library	User32.lib
DLL	User32.dll