当我在弹出窗口中按下按钮时更改屏幕上的文本输入字段Python Kivy

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

class MyLayout(BoxLayout):
    def __init__(self, **kwargs):
        super(MyLayout, self).__init__(**kwargs)
        self.orientation = 'vertical'
        
        self.text_input = TextInput(text='初始文本')
        self.add_widget(self.text_input)
        
        self.button = Button(text='更改文本', on_press=self.change_text)
        self.add_widget(self.button)

    def change_text(self, instance):
        self.text_input.text = '按钮按下，文本已更改'

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

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