Child Window Activation

Any number of child windows can appear in the client window at any one time, but only one can be active. The active child window is positioned in front of all other child windows, and its border is highlighted.

The user can activate an inactive child window by clicking it. An MDI application activates a child window by sending a WM_MDIACTIVATE message to the MDI client window. As the client window processes this message, it sends a WM_MDIACTIVATE message to the window procedure of the child window to be activated and to the window procedure of the child window being deactivated.

To prevent a child window from activating, handle the WM_NCACTIVATE message to the child window by returning FALSE.

Windows keeps track of each child window's position in the stack of overlapping windows. This stacking is known as the Z order. The user can activate the next child window in the Z order by choosing the Next command from the window menu in the active window. An application activates the next (or previous) child window in the Z order by sending a WM_MDINEXT message to the client window.

To retrieve the handle of the active child window, the MDI application sends a WM_MDIGETACTIVE message to the client window.

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