def _drawing_changed(self, old, new):
        """ Handles the container of drawing components changing.
        """
        if old is not None:
            self.component.remove( old )
        if new is not None:
#            new.bgcolor="pink"
            self.component.add( new )

        w, h = self.component.bounds
        self.component.position = [ self.pos[0] - (w/2), self.pos[1] - (h/2) ]
#        self.component.position = [ self.pos[0], self.pos[1] ]
        self.component.request_redraw()
Handles the container of drawing components changing.