如何让kivy只点击顶部小部件

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button

class TopWidget(Button):
    def on_touch_down(self, touch):
        if self.collide_point(*touch.pos):
            # 处理顶部小部件的点击事件
            print("顶部小部件被点击了")
        return super().on_touch_down(touch)

class RootWidget(BoxLayout):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.orientation = 'vertical'
        self.add_widget(TopWidget(text='顶部小部件'))
        self.add_widget(Button(text='其他小部件'))

class MyApp(App):
    def build(self):
        return RootWidget()

if __name__ == '__main__':
    MyApp().run()