如何在kivy中更新函数内部的布局

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout

class MyApp(App):
    def build(self):
        root = BoxLayout(orientation='vertical')
        return root

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

def update_layout():
    # 获取根部件
    root = App.get_running_app().root
    
    # 修改部件属性
    # root.ids.my_button.text = 'New Text'
    
    # 添加新部件
    # new_label = Label(text='New Label')
    # root.add_widget(new_label)
    
    # 删除部件
    # root.remove_widget(root.ids.my_button)

def build(self):
    root = BoxLayout(orientation='vertical')
    
    # 添加一个按钮
    button = Button(text='Update Layout')
    button.bind(on_release=update_layout)
    root.add_widget(button)
    
    return root