An MDI application controls the size and position of its child windows by sending messages to the MDI client window. To maximize the active child window, the application sends the WM_MDIMAXIMIZE message to the client window. When a child window is maximized, its client area completely fills the MDI client window. In addition, the system automatically hides the child window's title bar, and adds the child window's window menu icon and Restore button to the MDI application's menu bar. The application can restore the client window to its original (premaximized) size and position by sending the client window a WM_MDIRESTORE message.
An MDI application can arrange its child windows in either a cascade or tile format. When the child windows are cascaded, the windows appear in a stack. The window on the bottom of the stack occupies the upper left corner of the screen, and the remaining windows are offset vertically and horizontally so that the left border and title bar of each child window is visible. To arrange child windows in the cascade format, an MDI application sends the WM_MDICASCADE message. Typically, the application sends this message when the user clicks Cascade on the Window menu.
When the child windows are tiled, the system displays each child window in its entirety — overlapping none of the windows. All of the windows are sized, as necessary, to fit within the client window. To arrange child windows in the tile format, an MDI application sends a WM_MDITILE message to the client window. Typically, the application sends this message when the user clicks Tile on the Window menu.
An MDI application should provide a different icon for each type of child window it supports. The application specifies an icon when registering the child window class. The system automatically displays a child window's icon in the lower portion of the client window when the child window is minimized. An MDI application directs the system to arrange child window icons by sending a WM_MDIICONARRANGE message to the client window. Typically, the application sends this message when the user clicks Arrange Icons on the Window menu.