尝试在 MDTextField (KivyMD) 中访问后未显示用户文本

如何解决尝试在 MDTextField (KivyMD) 中访问后未显示用户文本

在使用 KivyMD 在 mddialog 中创建 MDTextField 后，我尝试访问用户在 MDTextField 中输入的文本并将标签的文本更改为输入的任何内容，但无济于事。这是我的代码如下：

# importing all the necessary modules and inheriting my dialog from Boxlayout

from kivymd.app import MDApp
from kivy.lang import Builder
from kivy.uix.Boxlayout import BoxLayout   
from kivymd.uix.dialog import mddialog     

# creating a string which will contain all my kv deFinitions that I would put in a .kv file

the_kv_file = '''
<ContentOfAppointmentDialog>:
    orientation: "vertical"
    spacing: "10dp"
    size_hint: None,None
    size: "250dp","150dp"

    MDTextField:
        hint_text: "Enter details"
        id: the_textfield
        helper_text: "Be detailed and precise"
        helper_text_mode: "on_focus"
        max_text_length: 75
        multiline: True
        mode: "rectangle"

    MDFlatButton:
        text: "disCARD"
        on_release: app.CloseDialog()
    MDFlatButton:
        text: "DONE"
        on_release: app.ChangingLabel()

MDFloatLayout:
   MDLabel:
       id: label_to_change
       text: "hello"
   MDFloatingActionButton:
       icon: 'pencil'
       on_press: app.OpenDialog()  
'''
# Creating the classes of My main app and the dialog as well as the required functions

class ContentOfAppointmentDialog(BoxLayout):    # this defines the dialogs layout
    pass


class MainApp(MDApp):   # my main app
    def build(self):
        self.main_screen = Builder.load_string(the_kv_file)
        self.dialog = mddialog(title="my example",type="custom",content_cls=ContentOfAppointmentDialog()) # defining the dialog
        self.AccessDialog = ContentOfAppointmentDialog()

        return self.main_screen

    def OpenDialog(self):   # opens dialog
        self.dialog.open()


    def CloseDialog(self):  # closes dialog
        self.dialog.dismiss()

# this is the function that is not working as I intended it to    
    def ChangingLabel(self):    # function that is supposed to change the label to what users input is
        self.main_screen.ids.label_to_change = self.AccessDialog.ids.the_textfield.text
        self.dialog.dismiss()


MainApp().run()