如何让KivyMD导航抽屉在单独的.py文件中调用其他应用程序？

from kivymd.app import MDApp
from kivymd.uix.navigationdrawer import NavigationLayout, MDNavigationDrawer

class MainApp(MDApp):
    def build(self):
        # 创建导航布局
        layout = NavigationLayout()

        # 创建导航抽屉
        drawer = MDNavigationDrawer()
        layout.add_widget(drawer)

        return layout

if __name__ == "__main__":
    MainApp().run()

from kivymd.app import MDApp
from kivymd.uix.screen import MDScreen

class App1(MDApp):
    def build(self):
        screen = MDScreen()
        # 添加其他应用程序的界面和功能
        return screen

if __name__ == "__main__":
    App1().run()

from kivymd.app import MDApp
from kivymd.uix.navigationdrawer import NavigationLayout, MDNavigationDrawer
from kivy.lang import Builder

class MainApp(MDApp):
    def build(self):
        # 创建导航布局
        layout = NavigationLayout()

        # 创建导航抽屉
        drawer = MDNavigationDrawer()
        drawer.add_widget(Builder.load_file("app1.kv"))  # 加载其他应用程序的界面
        layout.add_widget(drawer)

        return layout

if __name__ == "__main__":
    MainApp().run()