def METHOD_NAME(self):
    # insert canvas, if not already
    p_canvas = self.viewer.get_canvas()
    if not p_canvas.has_object(self.canvas):
        p_canvas.add(self.canvas)
    if not self.canvas.has_object(self.picker_obj):
        self.canvas.add(self.picker_obj)
    self.canvas.ui_set_active(True, viewer=self.viewer)