In general, an application must destroy all the windows it creates. It does this by using the WinDestroyWindow function. When a window is destroyed, the system hides the window, if it is visible, and then removes any internal data associated with the window. This invalidates the window handle so that it can no longer be used by the application.

An application destroys many of the windows it creates soon after creating them. For example, an application usually destroys a dialog window as soon as the application has sufficient input from the user to continue its task. An application eventually destroys the main window of the application (before terminating).

Destroying a window does not affect the window class from which the window was created. New windows still can be created using that class, and any existing windows of that class continue to operate.

When the application calls WinDestroyWindow, the system searches the descendancy tree for all windows below the specified window and destroys them from the bottom up, so each child receives WM_DESTROY before its parent. Each destroyed window is responsible for cleaning up its own resources in response to the WM_DESTROY message.

If a presentation space was created by the WinGetPS function for any of the windows to be destroyed, it must be released by calling the WinReleasePS function. The application must do this before calling the WinDestroyWindow function. If a presentation space is associated with the device context for the window, the application must disassociate or destroy the presentation space by using the GpiAssociate or GpiDestroyPS function before calling WinDestroyWindow. Failing to release a resource can cause an error.

For more information about presentation spaces and device contexts, see Painting and Drawing.

If the window being destroyed is the active window, both the active and focus states are transferred to another window. The window that becomes the active window is the next window, as determined by the Alt+Esc key combination. The new active window then determines which window receives the keyboard focus.