关闭kivy中的webview

from kivy.uix.boxlayout import BoxLayout
from kivy.lang import Builder
from kivy.core.window import Window

Builder.load_string('''
<WebviewContainer>:
    WebView:
        id: webview
        url: 'https://www.example.com'
''')

class WebviewContainer(BoxLayout):
    def __init__(self, **kwargs):
        super(WebviewContainer, self).__init__(**kwargs)
        Window.bind(on_request_close=self._on_request_close)

    def _on_request_close(self, *args):
        webview = self.ids.webview
        webview.unbind(on_loaded=self._on_webview_loaded)
        webview.unbind(on_error=self._on_webview_error)
        webview.unbind(on_finish=self._on_webview_finish)
        webview.unbind(on_abort=self._on_webview_abort)
        webview.unbind(on_update=self._on_webview_update)
        webview.unbind(on_progress=self._on_webview_progress)
        webview.stop()
        return False

from kivy.app import App

class MyWebApp(App):
    def build(self):
        return WebviewContainer()

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