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SetWindowSubclass function

Installs or updates a window subclass callback.

Syntax


BOOL SetWindowSubclass(
  _In_  HWND hWnd,
  _In_  SUBCLASSPROC pfnSubclass,
  _In_  UINT_PTR uIdSubclass,
  _In_  DWORD_PTR dwRefData
);

Parameters

hWnd [in]

Type: HWND

The handle of the window being subclassed.

pfnSubclass [in]

Type: SUBCLASSPROC

A pointer to a window procedure. This pointer and the subclass ID uniquely identify this subclass callback. For the callback function prototype, see SUBCLASSPROC.

uIdSubclass [in]

Type: UINT_PTR

The subclass ID. This ID together with the subclass procedure uniquely identify a subclass. To remove a subclass, pass the subclass procedure and this value to the RemoveWindowSubclass function. This value is passed to the subclass procedure in the uIdSubclass parameter.

dwRefData [in]

Type: DWORD_PTR

DWORD_PTR to reference data. The meaning of this value is determined by the calling application. This value is passed to the subclass procedure in the dwRefData parameter. A different dwRefData is associated with each combination of window handle, subclass procedure and uIdSubclass.

Return value

Type: BOOL

TRUE if the subclass callback was successfully installed; otherwise, FALSE.

Remarks

Subclass callbacks are identified by the combination of the callback address and the caller-defined subclass ID. If the callback address and ID pair have not yet been installed, then this function installs the subclass. If the pair has already been installed, then this function just updates the reference data.

Each callback can store a single DWORD of reference data, which is passed to the callback function when it is called to filter messages. No reference counting is performed for the callback; it may repeatedly call SetWindowSubclass to alter the value of its reference data element.

Warning  You cannot use the subclassing helper functions to subclass a window across threads.

Requirements

Minimum supported client

Windows XP [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]

Header

Commctrl.h

Library

Comctl32.lib

DLL

Comctl32.dll (version 5.8 or later)

See also

GetWindowSubclass
DefSubclassProc
RemoveWindowSubclass

 

 

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