在kivy中使用一个屏幕上另一个屏幕上的变量

from kivy.uix.screenmanager import Screen

class Screen1(Screen):
    variable = "Hello World"

from kivy.uix.screenmanager import ScreenManager, Screen

class Screen2(Screen):
    def get_variable(self):
        screen1 = self.manager.get_screen('screen1')
        variable_value = screen1.variable
        print(variable_value)

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

class MyApp(App):
    def build(self):
        sm = ScreenManager()
        sm.add_widget(Screen1(name='screen1'))
        sm.add_widget(Screen2(name='screen2'))
        return sm

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

Button:
    text: 'Get Variable'
    on_release: app.root.current = 'screen2'; screen2.get_variable()