如何在KivyMD (Python)中组合导航抽屉和多屏幕？

from kivymd.app import MDApp
from kivymd.uix.screen import MDScreen
from kivymd.uix.navigationdrawer import NavigationLayout
from kivymd.uix.button import MDFlatButton
from kivymd.uix.boxlayout import MDBoxLayout

class MainScreen(MDScreen):
    pass

class SecondScreen(MDScreen):
    pass

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

        # 创建导航抽屉
        nav_drawer = MDBoxLayout(orientation='vertical')
        nav_drawer.add_widget(MDFlatButton(text="主页", on_release=self.show_main_screen))
        nav_drawer.add_widget(MDFlatButton(text="第二页", on_release=self.show_second_screen))
        nav_layout.add_widget(nav_drawer)

        # 创建主屏幕
        self.main_screen = MainScreen()
        nav_layout.add_widget(self.main_screen)

        return nav_layout

    def show_main_screen(self, *args):
        # 切换到主屏幕
        self.root.ids.nav_layout.ids.scr_mngr.current = "main_screen"

    def show_second_screen(self, *args):
        # 切换到第二屏幕
        self.root.ids.nav_layout.ids.scr_mngr.current = "second_screen"

TestApp().run()