从另一个.py文件访问Python字典不会更新Kivy标签

from kivy.app import App
from kivy.uix.label import Label
from kivy.properties import StringProperty

class MyLabel(Label):
    text_value = StringProperty()  # 定义一个与字典值关联的属性

    def __init__(self, **kwargs):
        super(MyLabel, self).__init__(**kwargs)
        self.text_value = "初始值"  # 设置初始值

    def update_text(self, new_text):
        self.text_value = new_text  # 更新属性值

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

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

from kivy.lang import Builder
from kivy.app import App

Builder.load_string('''
<MyLabel>:
    text: root.text_value  # 将标签的text属性与属性绑定
''')

class AnotherClass:
    def __init__(self, app):
        self.app = app

    def update_label_text(self, new_text):
        self.app.root.update_text(new_text)  # 调用Kivy标签的更新方法

if __name__ == '__main__':
    app = App.get_running_app()
    another_class = AnotherClass(app)
    another_class.update_label_text("新的值")