delete-event
This is an event signal, fired when the window manager requests that a widget be deleted. This is generally when a user clicks the X close button on a toplevel window.
The delete event is not propagated. If you want to prevent the end user from using the window decorations to close your application, returning true from the "delete-event" signal will do just that. Allowing it to return false - which it does by default - will cause its default handler to be called. This happens to be the destroy() method, which in turns fires the "destroy" signal. In most cases, it's simpler to connect directly to the latter.
See also: "event".
Callback function
忘却曲線を使ってこの知識を確実に記憶に残す
