The 'onClose' callback

Event number: 10
Generated for: All objects, but usually applies to Window, Form, Document or Dialog, or an APL (child task) object.

The onClose callback indicates a request to close an object (usually a window). It can be generated as a result of the user clicking the close box of a window, or by the system. If you have defined an onClose callback, the window is not closed automatically; your onClose callback should do this if appropriate, by invoking the Close method with an argument of 1 to cause an unconditional close. You might also wish to delete the window as well.

The onClose callback is treated specially in one way. Normally when an APL callback is defined for an event, it is run after the system default handler for that event. The default handler for a Close event is to close and delete the object, but doing this would make it impossible for your onClose handler to suppress the close action. For this reason, setting the onClose callback property automatically disables the default system handler for the close event on that object.

For an APL (child task) object, the onClose callback is triggered when the child task is about to terminate for any reason.