Overridable method called when a view is unloaded (either on view change or on application shutdown).
        Handles by default the unregistering of all event handlers previously registered by
        the view.

def unload(self):
        """
        Overridable method called when a view is unloaded (either on view change or on application shutdown).
        Handles by default the unregistering of all event handlers previously registered by
        the view.
        """
        self.is_loaded = False
        for evt in self._event_cache:
            self.context.unregister(
                evt['event'], evt['callback'], evt['selector'])
        self._event_cache = {}