如何在Kivy上双击时回调和打印MDLabel的文本？

from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.behaviors import ButtonBehavior
from kivy.uix.image import Image
from kivy.clock import Clock

class MDLabel(BoxLayout, ButtonBehavior):
    def __init__(self, **kwargs):
        super(MDLabel, self).__init__(**kwargs)
        self.orientation = 'vertical'
        self.label = Label(text='Hello Kivy!')
        self.add_widget(self.label)
        self.bind(on_double_tap=self.on_double_tap)

    def on_double_tap(self, *args):
        print(self.label.text)

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

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