无法更新kivy进度条

from kivy.app import App
from kivy.uix.progressbar import ProgressBar
from kivy.uix.boxlayout import BoxLayout
from kivy.clock import Clock

class ProgressApp(App):
    def build(self):
        layout = BoxLayout(orientation='vertical')
        self.progress = ProgressBar(max=100)
        layout.add_widget(self.progress)
        Clock.schedule_interval(self.update_progress, 1)  # 每秒更新一次进度
        return layout

    def update_progress(self, dt):
        if self.progress.value < self.progress.max:
            self.progress.value += 10
        else:
            self.progress.value = 0

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