如何使用.py文件在kivy中添加导航？

from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen

# 导入自定义的.py文件
from screen1 import Screen1
from screen2 import Screen2

class MyApp(App):
    def build(self):
        # 创建ScreenManager对象
        sm = ScreenManager()

        # 添加屏幕或导航页面
        sm.add_widget(Screen1(name='screen1'))
        sm.add_widget(Screen2(name='screen2'))

        # 将ScreenManager对象添加到根部件
        return sm

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

from kivy.uix.screenmanager import Screen
from kivy.uix.button import Button

class Screen1(Screen):
    def build(self):
        # 构建屏幕1的布局和组件
        button = Button(text='Go to Screen 2')
        button.bind(on_release=self.switch_screen)
        self.add_widget(button)

    def switch_screen(self, instance):
        # 切换到屏幕2
        self.manager.current = 'screen2'

from kivy.uix.screenmanager import Screen
from kivy.uix.button import Button

class Screen2(Screen):
    def build(self):
        # 构建屏幕2的布局和组件
        button = Button(text='Go to Screen 1')
        button.bind(on_release=self.switch_screen)
        self.add_widget(button)

    def switch_screen(self, instance):
        # 切换到屏幕1
        self.manager.current = 'screen1'