如何在Kivy上按下按钮时显示文本

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

class MyApp(App):
    def update_label(self, button):
        self.label.text = "Button pressed!"

    def build(self):
        layout = BoxLayout(orientation='vertical')
        button = Button(text='Press me')
        button.bind(on_press=self.update_label)
        self.label = Label(text='Label')
        layout.add_widget(button)
        layout.add_widget(self.label)
        return layout

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