KivyMD//Python如何创建加载对话框(弹出窗口)，该对话框在代码在后台运行另一个函数时显示旋转轮

pip install kivy
pip install kivymd

from kivymd.app import MDApp
from kivymd.uix.dialog import MDDialog
from kivymd.uix.label import MDLabel
from kivy.lang import Builder
from kivy.clock import Clock

class MyApp(MDApp):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.dialog = None

    def show_loading_dialog(self):
        content = MDLabel(text="Loading...", halign="center")

        self.dialog = MDDialog(
            title="",
            content=content,
            size_hint=(0.5, None),
            height=dp(120),
        )
        self.dialog.open()
        Clock.schedule_once(self.run_background_function)

    def run_background_function(self, *args):
        # 在此处运行后台函数
        pass

    def on_stop(self):
        if self.dialog:
            self.dialog.dismiss()

    def build(self):
        return Builder.load_string(
            '''
BoxLayout:
    orientation: 'vertical'

    MDToolbar:
        title: 'KivyMD Loading Dialog'

    MDRaisedButton:
        text: 'Show Loading Dialog'
        pos_hint: {'center_x': 0.5}
        on_release: app.show_loading_dialog()
            '''
        )

MyApp().run()