KivyMD AttributeError: 'NoneType' object has no attribute 'theme_cls'

Question

I'm having trouble getting KivyMD working, I've read so many of the questions on here about this error but none of them have worked. The below is a minimum runnable example, I know the issue is with the code in the MyApp class but I don't know exactly why it isn't working. Thanks in advance for your help

main.py

import kivy
from kivy.app import App
from kivy.properties import ObjectProperty, StringProperty, NumericProperty, ListProperty
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.lang import Builder
from kivy.uix.popup import Popup
from kivy.uix.label import Label
from kivy.uix.button import Button
from kivy.core.window import Window
from kivymd.theming import ThemeManager
import mysql.connector


Window.clearcolor = (1,1,1,1)


class Information(Screen):
    pass


class WindowManager(ScreenManager):
    pass


kv = Builder.load_file("kivy.kv")
sm = WindowManager()

screens = [Information(name="information")]
for screen in screens:
    sm.add_widget(screen)

sm.current = "information"


class MyApp(App):
    theme_cls = ThemeManager()

    def build(self):
        return sm


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

kivy.kv

<Information>:
    name: "information"

    FloatLayout:

        ActionBar:
            pos_hint: {'top': 1}
            ActionView:
                background_image: ""
                background_color: 0.2,0.6,1,1
                ActionPrevious:
                    app_icon: "white menu.png"
                    with_previous: False
                ActionOverflow:
                ActionButton:
                    app_icon: "close.png"
                    on_release: print("Button pressed")

        MDRaisedButton:
            text: "Test"

Full Error

 AttributeError: 'NoneType' object has no attribute 'theme_cls'
   File "C:\Users\user\AppData\Local\Programs\Python\Python37-32\lib\site-packages\kivy\lang\builder.py", line 696, in _apply_rule
     setattr(widget_set, key, value)
   File "kivy\weakproxy.pyx", line 35, in kivy.weakproxy.WeakProxy.__setattr__
   File "kivy\properties.pyx", line 497, in kivy.properties.Property.__set__
   File "kivy\properties.pyx", line 544, in kivy.properties.Property.set
   File "kivy\properties.pyx", line 599, in kivy.properties.Property.dispatch
   File "kivy\_event.pyx", line 1214, in kivy._event.EventObservers.dispatch
   File "kivy\_event.pyx", line 1120, in kivy._event.EventObservers._dispatch
   File "kivy\properties.pyx", line 1318, in kivy.properties.ReferenceListProperty.trigger_change
   File "kivy\properties.pyx", line 1333, in kivy.properties.ReferenceListProperty.trigger_change
   File "kivy\properties.pyx", line 599, in kivy.properties.Property.dispatch
   File "kivy\_event.pyx", line 1214, in kivy._event.EventObservers.dispatch
   File "kivy\_event.pyx", line 1120, in kivy._event.EventObservers._dispatch
   File "C:\Users\user\AppData\Local\Programs\Python\Python37-32\lib\site-packages\kivymd\uix\elevation.py", line 126, in _update_shadow
     self._shadow = App.get_running_app().theme_cls.quad_shadow

Answer 1

You just need to do your Builder.load_file() after the MyApp class is defined. You can move it inside the build() method:

class MyApp(App):
    theme_cls = ThemeManager()

    def build(self):
        kv = Builder.load_file("kivy.kv")
        sm = WindowManager()

        screens = [Information(name="information")]
        for screen in screens:
            sm.add_widget(screen)

        sm.current = "information"
        return sm


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