如何在kivy语言和python类中将按钮放在按钮上方

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

class CustomLayout(BoxLayout):
    def __init__(self, **kwargs):
        super(CustomLayout, self).__init__(**kwargs)
        
        # 创建按钮
        button1 = Button(text='按钮1')
        button2 = Button(text='按钮2')
        
        # 将按钮添加到布局中
        self.add_widget(button1)
        self.add_widget(button2)
        
        # 设置按钮的位置
        button1.pos_hint = {'center_x': 0.5, 'center_y': 0.5}
        button2.pos_hint = {'center_x': 0.5, 'center_y': 0.5}
        
        # 设置按钮的大小
        button1.size_hint = (None, None)
        button2.size_hint = (None, None)
        button1.size = (100, 50)
        button2.size = (100, 50)
        
        # 将按钮放在按钮上方
        self.bind(minimum_height=self.setter('height'))

class MyApp(App):
    def build(self):
        return CustomLayout()

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