如何定义当用户在TextInput中输入文本并在Kivy中按enter键时发生的情况?

我正在尝试使用Kivy和Python创建一个简单的聊天机器人应用程序UI,但我还停留在第一阶段。 如何访问BoxLayout中的TextInput小部件以获取其内容?

我读到函数 on\u text\u validate() 每当您在TextInput上按“Enter”时调用。然而,下面的代码似乎不起作用。

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label
from kivy.uix.textinput import TextInput
from kivy.uix.screenmanager import Screen, ScreenManager, FadeTransition
from kivy.uix.scrollview import ScrollView
from kivy.properties import StringProperty
from kivy.lang import Builder

Builder.load_string('''
#:import AnchorLayout kivy.uix.anchorlayout
#:import Layout kivy.uix.layout
<ChatBotScreen>:
    BoxLayout:
        orientation: 'vertical'

        ScrollView:
            Label:
                size_hint_y: None
                height: self.texture_size[1]
                text_size: self.width, None
                botOutput: root.botOutput
        ScrollView:
            Label:
                size_hint_y: None
                height: self.texture_size[1]
                text_size: self.width, None
                userInput: root.userInput
        TextInput:
            id: ti_userinput
            multiline: False
''')

class ChatBotScreen(Screen):
    userInput = StringProperty()
    botOutput = StringProperty()

    def on_text_validate(self):
        text_input_userInput = self.ids['ti_userinput'].text
        self.ids['ti_userinput'].text = ''
        print(text_input_userInput)

    def UserInput(self):
        pass
    def BotOutput(self):
        pass

sm = ScreenManager(transition=FadeTransition())
sm.add_widget(ChatBotScreen(name='mainchat'))    

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

请引导我。