提交按钮的Kivy绑定文本输入提供文本：'NoneType‘对象没有属性'text’

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

class MyBoxLayout(BoxLayout):
    def __init__(self, **kwargs):
        super(MyBoxLayout, self).__init__(**kwargs)
        
        self.orientation = 'vertical'
        
        self.text_input = TextInput()
        self.add_widget(self.text_input)
        
        self.submit_button = Button(text='提交')
        self.submit_button.bind(on_release=self.submit)
        self.add_widget(self.submit_button)
        
    def submit(self, instance):
        text = self.text_input.text
        # 在这里可以进行提交操作，例如保存文本到数据库或进行其他处理
        print('提交的文本：', text)

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

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