当我到达容纳对象的屏幕时，如何在ScreenManager中使用小部件进行移动？

from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.button import Button
from kivy.uix.floatlayout import FloatLayout
from kivy.animation import Animation

class MyScreenManager(ScreenManager):
    def __init__(self, **kwargs):
        super(MyScreenManager, self).__init__(**kwargs)
        self.transition = None

class MyScreen(Screen):
    def __init__(self, **kwargs):
        super(MyScreen, self).__init__(**kwargs)
        self.layout = FloatLayout()
        self.button = Button(text='Move me!', size_hint=(None, None), pos=(100, 100))
        self.layout.add_widget(self.button)
        self.add_widget(self.layout)

    def on_enter(self):
        # 在进入屏幕时触发
        animation = Animation(pos=(300, 300), duration=1)
        animation.start(self.button)

class MyApp(App):
    def build(self):
        screen_manager = MyScreenManager()
        screen_manager.add_widget(MyScreen(name='screen1'))
        return screen_manager

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