Size and Position Messages

Windows sends the WM_GETMINMAXINFO message to a window whose size or position is about to change. For example, the message is sent when the user chooses the Move or Size command from the window menu or clicks the sizing border or title bar; the message is also sent when an application calls SetWindowPos to move or size the window. WM_GETMINMAXINFO includes a pointer to a MINMAXINFO structure containing the default maximized size and position for the window, as well as the default minimum and maximum tracking sizes. An application can override the defaults by processing WM_GETMINMAXINFO and setting the appropriate members of MINMAXINFO. A window must have the WS_THICKFRAME or WS_CAPTION style to receive WM_GETMINMAXINFO. A window with the WS_THICKFRAME style receives this message during the window-creation process, as well as when it is being moved or sized.

Windows sends the WM_WINDOWPOSCHANGING message to a window whose size, position, position in the Z order, or show state is about to change. This message includes a pointer to a WINDOWPOS structure that specifies the window's new size, position, position in the Z order, and show state. By setting the members of WINDOWPOS, an application can affect the window's new size, position, and appearance.

After changing a window's size, position, position in the Z order, or show state, Windows sends the WM_WINDOWPOSCHANGED message to the window. This message includes a pointer to WINDOWPOS that informs the window of its new size, position, position in the Z order, and show state. Setting the members of the WINDOWPOS structure that is passed with WM_WINDOWPOSCHANGED has no effect on the window. A window that must process WM_SIZE and WM_MOVE messages must pass WM_WINDOWPOSCHANGED to the DefWindowProc function; otherwise, Windows does not send WM_SIZE and WM_MOVE messages to the window.

Windows sends the WM_NCCALCSIZE message to a window when the window is created or sized. Windows uses the message to calculate the size of a window's client area and the position of the client area relative to the upper left corner of the window. A window typically passes this message to the default window procedure; however, this message can be useful in applications that customize a window's nonclient area or preserve portions of the client area when the window is sized. For more information about window size, see Painting and Drawing.

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