An application sends the WM_MDIMAXIMIZE message to a multiple document interface (MDI) client window to maximize an MDI child window. Windows resizes the child window to make its client area fill the client window. Windows places the child window’s window menu icon in the rightmost position of the frame window’s menu bar, and places the child window’s restore icon in the leftmost position. Windows also appends the title bar text of the child window to that of the frame window.
WM_MDIMAXIMIZE wParam = (WPARAM) (HWND) hwndMax; // handle of child to maximize lParam = 0; // not used; must be zero
The return value is always zero.
If an MDI client window receives any message that changes the activation of its child windows while the currently active MDI child window is maximized, Windows restores the active child window and maximizes the newly activated child window.