window

Arguments: dialog-item

Returns the widget-window instance for a widget when it is currently on a parent window, and otherwise returns nil. The argument should be an instance of a dialog-item subclass.

Due to a legacy design decision in Common Graphics, a widget is implemented as two separate objects. The logical object that an application normally deals with is an instance of a dialog-item subclass, and is alternately called either a dialog-item, a widget, a control, or a component in our documentation (though "component" can refer to other interface objects as well).

When a dialog-item is placed onto a parent window (by including it in the :dialog-items argument to make-window or by calling add-component), then the second object, a widget-window instance, is created internally to implement the window that then appears on the screen for the widget. If the parent window is later closed, or if the widget is removed from the parent window by calling remove-component, then the widget-window is destroyed and the window of the widget will again be nil.

Most applications should be able to work with the dialog-item only. If needed, though, an application could pass the window of a widget to any function that takes a window (basic-pane) argument. And if an application needs to add methods to a generic function that will be called on the window of a widget rather than on the widget itself, then the method could specialize on the widget-window class. This generally requires defining subclasses for both the dialog-item class and the widget-window class, and then adding a trivial widget-device method that tells the dialog-item subclass which widget-window subclass to instantiate internally when it is added to a parent window.

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This page was not revised from the 9.0 page.
Created 2015.5.21.