An application sends the WM_MDISETMENU message to a multiple document interface (MDI) client window to replace the entire menu of an MDI frame window, to replace the Window menu of the frame window, or both.
WM_MDISETMENU wParam = (WPARAM) (HMENU) hmenuFrame; // handle of frame menu lParam = (LPARAM) (HMENU) hmenuWindow; // handle of Window menu
If the message succeeds, the return value is the handle of the old frame window menu.
If the message fails, the return value is zero.
After sending this message, an application must call the DrawMenuBar function to update the menu bar.
If this message replaces the Window menu, the MDI child window menu items are removed from the previous Window menu and added to the new Window menu.
If an MDI child window is maximized and this message replaces the MDI frame window menu, the System menu icon and restore icon are removed from the previous frame window menu and added to the new frame window menu.