Dynamically setting attributes to MDTextField in KivyMD

Question

I have code below which dynamically creates a bunch of text fields in KivyMD. However, one attribute I need to set, on_text, will not accept my settings through python (no error thrown, just a blank field on debug), but will accept them through KV.

My questions are: Why is it not accepting my on_text update, and how can I work around it programmatically while maintaining python/KV separation?

Here's the python code:

from kivy.clock import mainthread
from kivymd.app import MDApp
from kivymd.icon_definitions import md_icons
from kivymd.uix.textfield import MDTextField
from kivy.uix.screenmanager import Screen, ScreenManager, NoTransition
from kivy.uix.widget import Widget
from kivy.core.window import Window
from kivymd.uix.gridlayout import GridLayout
from kivy.lang import Builder

Builder.load_file('./main.kv')
        
class HomeScreen(Screen):

    def build(self):
        return HomeScreen()

        
class PRApp(MDApp):

    def build(self):
        self.theme_cls.theme_style = "Light"
        self.theme_cls.primary_palette = "Gray"
        self.sm = ScreenManager(transition=NoTransition())
        self.sm.add_widget(HomeScreen(name="home_screen"))

        return self.sm

    def add_rm_textboxes(self):  # sourcery skip: use-fstring-for-concatenation
        for i in range(1,21):
            textbox = MDTextField(hint_text=str(i)+" RM",mode="fill",helper_text="Enter your TESTED "+str(i)+" RM",helper_text_mode="on_focus")
            textbox.on_text = print(textbox.text)
            textbox.name = "rm"+str(i)
            self.sm.current_screen.ids.pr_grid.add_widget(textbox)

    def wait(self):
        pass
            


PRApp().run()

And here's my KV code:

<HomeScreen>:
    id: home_screen
    BoxLayout:
        orientation: 'vertical'

        MDBottomNavigation:

            id: bottom_nav

            MDBottomNavigationItem:
                name: 'home_screen'
                text: "Home"
                icon: 'home'
                BoxLayout:
                    orientation: 'vertical'

                    MDToolbar:
                        title: "PR!"
                        anchor_title: 'center'

                    MDLabel:
                        text: "This is the home screen"
                        halign: 'center'

            MDBottomNavigationItem:
                name: 'routine_screen'
                text: "Routines"
                icon: 'notebook'
                on_tab_press: app.wait()

                MDLabel:
                    text: "Routines"
                    halign: 'center'


            MDBottomNavigationItem:
                name: 'profile_screen'
                text: "Profile"
                icon: 'account-circle-outline'
                on_tab_press: app.add_rm_textboxes()

                MDLabel:
                    text: "Profile"
                    halign: 'center'


                MDGridLayout:
                    id: pr_grid
                    cols: 2

Answer 1

Whenever you bind a callback to an event or a property that callback is supposed to be a function / method (name) not what it returns. That's why you got None when you did textbox.bind(text = print("test")), you could've done it like, textbox.bind(text = lambda *args : print("test")). Also note that a property callback is different from an event callback in kivy.

Here is a modified version of that portion,

    def add_rm_textboxes(self):  # sourcery skip: use-fstring-for-concatenation
        for i in range(1,21):
            textbox = MDTextField(hint_text=str(i)+" RM",mode="fill",helper_text="Enter your TESTED "+str(i)+" RM",helper_text_mode="on_focus")
            textbox.bind(text = self.callback_method)
#            textbox.bind(text = lambda *args : print("test"))
            textbox.name = "rm"+str(i)
            self.sm.current_screen.ids.pr_grid.add_widget(textbox)


    def callback_method(self, txtbx, txt):
        print(f"{txtbx.text = }, {txt = }, {txtbx.name = }")