subclass-widget

Arguments: dialog-item

Use of this function is deprecated. Common Graphics now always internally calls this function on all Microsoft widgets, and so there is never a need for an application to call it. Calling this function will now simply do nothing.

Performs what might be called "MS subclassing" on the window of dialog-item. This has nothing to do with CLOS classes, but rather causes lisp to intercept all low-level messages that are sent to widget windows and are normally handled within the Windows operating system where these widgets are implemented. All low-level Windows events for dialog-item will be passed to the pc:control-procedure generic function. In addition, the keypress and mouse-click events will call an event method for the dialog-item's window and that event.

You need to call subclass-widget only if you want to handle these low-level Windows events that are usually handled by MS-Windows internally. For example, when a user types a new value into an (single-line) editable-text widget, you normally know only what the new string and the old string are; if you want to know what actual key was pressed, then you will need to call subclass-widget and then write an event method on the window to handle the keypress event. Or you may want to intercept a mouse click on a widget even when its value is not changed by the click.

If subclass-widget is called on a widget that is already subclassed, no action is taken and nil is returned, otherwise t is returned.

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This page was not revised from the 10.0 page.
Created 2019.8.20.