Child Window Creation

To create a child window, an MDI application either calls the CreateMDIWindow function or sends the WM_MDICREATE message to the MDI client window. A more efficient way to create an MDI child window is to call the CreateWindowEx function, specifying the WS_EX_MDICHILD extended style. A thread in an MDI application can use CreateMDIWindow or CreateWindowEx to create a child window in a different thread. The WM_MDICREATE message is used only in the context of the same thread.

To destroy a child window, an MDI application sends a WM_MDIDESTROY message to the MDI client window.