Called by a row when its height changes, triggering the graphic frame
        to recalculate its total height (as the sum of the row heights).

def notify_height_changed(self):
        """
        Called by a row when its height changes, triggering the graphic frame
        to recalculate its total height (as the sum of the row heights).
        """
        new_table_height = sum([row.height for row in self.rows])
        self._graphic_frame.height = new_table_height