WM_WINDOWPOSCHANGING

The WM_WINDOWPOSCHANGING message is sent to a window whose size, position, or place in the Z order is about to change as a result of a call to the SetWindowPos function or another window-management function.

WM_WINDOWPOSCHANGING 
lpwp = (LPWINDOWPOS) lParam; // points to size and position data 
 

Parameters

lpwp

Value of lParam. Pointer to a WINDOWPOS structure that contains information about the window's new size and position.

Return Values

If an application processes this message, it should return zero.

Default Action

For a window with the WS_OVERLAPPED or WS_THICKFRAME style, the DefWindowProc function sends the WM_GETMINMAXINFO message to the window. This is done to validate the new size and position of the window and to enforce the CS_BYTEALIGNCLIENT and CS_BYTEALIGNWINDOW client styles. By not passing the WM_WINDOWPOSCHANGING message to the DefWindowProc function, an application can override these defaults.

Remarks

While this message is being processed, modifying any of the values in WINDOWPOS affects the window's new size, position, or place in the Z order. An application can prevent changes to the window by setting or clearing the appropriate bits in the flags member of WINDOWPOS.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Unsupported.
  Header: Declared in winuser.h.

See Also

Windows Overview, Window Messages, DefWindowProc, EndDeferWindowPos, SetWindowPos, WINDOWPOS, WM_GETMINMAXINFO, WM_MOVE, WM_SIZE, WM_WINDOWPOSCHANGED