如何在Kivy的滚动视图上创建一个固定按钮？

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

class MyLayout(BoxLayout):
    def __init__(self, **kwargs):
        super(MyLayout, self).__init__(**kwargs)
        
        # 创建一个按钮
        button = Button(text='固定按钮', size_hint=(None, None), size=(150, 50))
        
        # 创建一个滚动视图
        scroll_view = ScrollView()
        
        # 创建一个包含多个按钮的布局
        buttons_layout = BoxLayout(orientation='vertical', size_hint_y=None, spacing=10)
        buttons_layout.bind(minimum_height=buttons_layout.setter('height'))
        
        # 向布局中添加多个按钮
        for i in range(20):
            button = Button(text=f'按钮 {i+1}', size_hint=(None, None), size=(150, 50))
            buttons_layout.add_widget(button)
        
        # 将按钮布局添加到滚动视图中
        scroll_view.add_widget(buttons_layout)
        
        # 将按钮和滚动视图添加到自定义布局中
        self.add_widget(button)
        self.add_widget(scroll_view)

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

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