This event handler can be reimplemented in a subclass to receive widget hide events. The event is passed in the event parameter.
Hide events are sent to widgets immediately after they have been hidden.
Note: A widget receives spontaneous show and hide events when its mapping status is changed by the window system, e.g. a spontaneous hide event when the user minimizes the window, and a spontaneous show event when the window is restored again. After receiving a spontaneous hide event, a widget is still considered visible in the sense of isVisible().