void MDIActivate( CWnd* pWndActivate );
pWndActivate
Points to the MDI child window to be activated.
Activates a different MDI child window. The WM_MDIACTIVATE message is sent to both the child window being activated and the child window being deactivated.
An MDI child window is activated independently of the MDI frame window. When the frame becomes active, the child window that was last activated is sent a WM_NCACTIVATE message to draw an active window frame and caption bar, but it does not receive another WM_MDIACTIVATE message.
CMDIFrameWnd::MDIGetActive, CMDIFrameWnd::MDINext, WM_ACTIVATE, WM_NCACTIVATE