How to disable a widget when a button from a different class is pressed? - kivy

Question

Im making a Button which disables a TopAppBar menu form my user interface, the problem is that the Button is on one class an the TopAppBar in another, because one belongs to the screen and the other is shared between multiple screens.
code:
from kivymd.app import MDApp
from kivy.lang import Builder
from kivy.core.window import Window
from kivymd.uix.screen import MDScreen
Window.size = (300, 500)
navigation_helper = """
<UserScreen>
name: 'user_screen'
MDBoxLayout:
orientation: "vertical"
pos_hint: {"top": 1}
adaptive_height: True
padding: (0, "80dp" , 0, 0)
FloatLayout:
MDRaisedButton:
id: save_btn_user
text: "Guardar"
md_bg_color: "white"
text_color: "black"
font_size: 16.2
pos_hint: {"left":1, "bottom": 1}
size_hint: (.2,.2)
disabled: True
on_press: root.save_btn_press()
MDRaisedButton:
id: edit_btn_user
text: "Editar"
md_bg_color: "white"
text_color: "black"
font_size: 16.2
pos_hint: {"right":1, "bottom": 1}
size_hint: (.2,.2)
disabled: False
on_press:
root.disable_top_bar()
<MainScreen>:
name: "main_screen"
BoxLayout:
orientation: 'vertical'
MDTopAppBar:
id: title_bar
title: 'Dietas'
md_bg_color: 0.08,0.07,0.45
specific_text_color: 1,1,1
left_action_items: [["menu", lambda x: nav_drawer.set_state('toggle')]]
Widget:
MDNavigationLayout:
ScreenManager:
id: scr
UserScreen:
MDNavigationDrawer:
id: nav_drawer
BoxLayout:
orientation: 'vertical'
spacing: '8dp'
ScrollView:
MDList:
OneLineIconListItem:
text: 'Usuario'
on_press:
scr.current= 'user_screen'
title_bar.title = "Usuario"
nav_drawer.set_state('close')
IconLeftWidgetWithoutTouch:
icon: 'account'
on_press:
scr.current= 'user_screen'
title_bar.title = "Usuario"
nav_drawer.set_state('close')
MainScreen:
"""
class UserScreen(MDScreen):
def disable_top_bar(self):
self.a=MainScreen()
self.a.disable_top_barr()
class MainScreen(MDScreen):
def disable_top_barr(self):
self.ids.title_bar.disabled = True
print("testmsg")
class DemoApp(MDApp):
def build(self):
self.theme_cls.theme_style = ("Dark")
screen = Builder.load_string(navigation_helper)
return screen
DemoApp().run()
As you may have seen, I tried creating two method, one in the TopAppBar class disabling it and printing a test message(that its shown) and the other in the Button class calling that function.

Answer 1

With the following approach
def disable_top_bar(self):
self.a=MainScreen()
self.a.disable_top_barr()
you will see no change in your GUI because each time you call that method, it will create a new instance of MainScreen (which is not related to your GUI) and call the asked method on it.
In order to access that specific instance you can use the method get_running_app of MDApp as follows,
def disable_top_bar(self):
# First access the running app instance.
app = MDApp.get_running_app()
# Access the target screen that you set as the root widget.
main_screen = app.root
# Call the method.
main_screen.disable_top_barr()
As a note avoid using predefined names like a, b, g etc. when working with KivyMD widgets.