在kivy中输入文本时，如何使用提示或弹出提示？

from kivy.uix.textinput import TextInput
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout

class MyBoxLayout(BoxLayout):
    def __init__(self, **kwargs):
        super(MyBoxLayout, self).__init__(**kwargs)
        self.orientation = 'vertical'
        self.text_input = TextInput(hint_text='请输入文本')
        self.add_widget(self.text_input)

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

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

from kivy.uix.textinput import TextInput
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.popup import Popup
from kivy.uix.label import Label

class MyBoxLayout(BoxLayout):
    def __init__(self, **kwargs):
        super(MyBoxLayout, self).__init__(**kwargs)
        self.orientation = 'vertical'
        self.text_input = TextInput()
        self.text_input.bind(on_text_validate=self.show_popup)
        self.add_widget(self.text_input)

    def show_popup(self, instance):
        popup = Popup(title='提示', content=Label(text='您输入的文本是：' + instance.text), size_hint=(None, None), size=(400, 200))
        popup.open()

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

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