Please help! App showing only black window!

Busola Oronti

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Apr 22, 2025, 1:47:56 PMApr 22

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Hi everyone,

Please I need your help! I'm relatively new to kivy and KivyMD.

I'm trying to build an app that has two screens at the moment - the Login and Home Screen. I got the code to run, but it only shows black screen. Do you know what I'm doing wrong?

Below is my code:

import os

from kivy.lang import Builder
from kivymd.app import MDApp
from kivymd.uix.screenmanager import MDScreenManager
from kivymd.uix.screen import MDScreen
#from kivymd.uix.appbar import MDActionBottomAppBarButton

# Simulated user credentials for authentication
user_credentials = {
    "admin": "admin123",
    "user": "user123",
    "test": "test123",
}

# Authentication function
def authenticate(username, password):
    return user_credentials.get(username) == password

KV = '''
#:import MDTopAppBar kivymd.uix.appbar.MDTopAppBar
#:import MDBottomAppBar kivymd.uix.appbar.MDBottomAppBar
#:import MDIconButton kivymd.uix.button.MDIconButton
#:import MDLabel kivymd.uix.label.MDLabel
#:import MDTextField kivymd.uix.textfield.MDTextField
#:import MDCard kivymd.uix.card.MDCard
#:import FitImage kivymd.uix.fitimage.FitImage
##:import MDActionBottomAppBarButton kivymd.uix.appbar.MDActionBottomAppBarButton

MDScreenManager:
    #id: screen_manager

    #LoginScreen:
    #HomeScreen:

<LoginScreen>:
    name: "login"
    #MDScreen:
    radius: [25, 25, 25, 25]
    md_bg_color: app.theme_cls.backgroundColor

    MDBoxLayout:
        orientation: "vertical"
        size_hint: 0.9, 0.9  # Essential for full-screen expansion
        spacing: "20dp"
        padding: "10dp"
        #md_bg_color: app.theme_cls.primaryColor

        MDCard:
            orientation: "vertical"
            adaptive_size: True
            theme_bg_color: "Custom"
            md_bg_color: self.theme_cls.backgroundColor
            padding: 10
            radius: [15]
            
            FitImage:
                source: "login_image2.png" if os.path.exists("login_image2.png") else ""
                pos_hint: {"top": 1}
                size_hint: 1, None
                fit_mode: "contain"
                height: "150dp"  # Explicit height for the image

        MDTextField:
            id: username_input
            hint_text: "Username"
            size_hint: 1, None
            height: "40dp"
            pos_hint: {"center_x": 0.5}

        MDTextField:
            id: password_input
            hint_text: "Password"
            password: True
            size_hint: 1, None
            height: "40dp"
            pos_hint: {"center_x": 0.5}
            icon_right: "eye-off-outline"
            icon_right_color: app.theme_cls.primary_color
            on_icon_right_release: app.toggle_password_visibility(self)

        Widget:
            size_hint_y: None
            height: "20dp"        
    
        MDButton:
            style: "elevated"
            theme_shadow_color: "Custom"
            shadow_color: "grey"
            pos_hint: {"center_x": .5, "center_y": .5}
            size_hint: 0.5, None
            height: "40dp"
            on_release: 
                app.validate_user(
                username_input.text, 
                password_input.text,
                )

                MDButtonText:
                    text: "Login"
                    font_style: "Title"

        MDLabel:
            id: result_label
            text: ""
            halign: "center"
            markup: True
            size_hint_y: None
            height: "30dp"

<HomeScreen>:
    name: "home"
    
    MDBoxLayout:
        orientation: "vertical"
        
        MDTopAppBar:
            title: "Home Screen"
            left_action_items: [["logout", lambda x: app.logout()]]
            
        MDLabel:
            text: "Welcome to the Home Screen!"
            halign: "center"
'''
class LoginScreen(MDScreen):
    pass

class HomeScreen(MDScreen):
    pass

class ACORNApp(MDApp):
    def file_exists(self, filename):
        return os.path.exists(filename)
    
    def build(self):
        self.theme_cls.primary_palette = "Teal"
        self.theme_cls.theme_style = "Dark"
        #return Builder.load_string(KV)
        #return MDScreenManager()

        # Create screen manager
        self.sm = MDScreenManager()
        self.sm.add_widget(LoginScreen())
        self.sm.add_widget(HomeScreen())

        return self.sm
    
    def toggle_password_visibility(self, text_field):
        """
        Toggles the visibility of the password in the given MDTextField.
        """
        if text_field.password:
            text_field.password = False
            text_field.icon_right = "eye-outline"  # Change icon to show password
        else:
            text_field.password = True
            text_field.icon_right = "eye-off-outline"  # Change icon to hide password
    
    
    def validate_user(self, username, password):
        """
        Validates the username and password entered by the user.
        """
        if authenticate(username, password):
            self.sm.current = "home"  # Switch to the HomeScreen
        else:
            self.sm.get_screen("login").ids.result_label.text = "[color=#FF0000]Invalid username or password[/color]"

    def logout(self):
        """
        Logs the user out and switches back to the LoginScreen.
        """

        # Clear the login fields
        login_screen = self.sm.get_screen("login")
        login_screen.ids.username_input.text = ""
        login_screen.ids.password_input.text = ""
        login_screen.ids.result_label.text = ""
        
        self.sm.current = "login"  # Switch back to the LoginScreen


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

Thanks!

Bussy

Busola Oronti

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Apr 22, 2025, 2:20:09 PMApr 22

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I'm using Kivymd 2.0.1 dev 0 if this helps.

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ElliotG

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Apr 22, 2025, 9:13:05 PMApr 22

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You have defined the root widget, the screen manger in kv. You also have the screens defined in kv, so you need to load the kv string. I removed the code where you also created the screenmanager in python. In the App class you can access the root widget, your screen manger, as self.root.

I made a few other changes so you can run the code and move forward.

from kivy.lang import Builder
from kivymd.app import MDApp

from kivymd.uix.screen import MDScreen

# Simulated user credentials for authentication
user_credentials = {
"admin": "admin123",
"user": "user123",
"test": "test123",
}

# Authentication function

def authenticate(username, password):

# return user_credentials.get(username) == password # this is not correct...
# assuming the username should be "user123" and the password should be "test123"
return user_credentials.get('user') == username and user_credentials.get('test') == password

KV = '''
#:import os os

MDScreenManager:
LoginScreen:
HomeScreen:

<LoginScreen>:
name: "login"

icon_right_color: app.theme_cls.primary_palette
# on_icon_right_release: app.toggle_password_visibility(self)

def build(self):
self.theme_cls.primary_palette = "Teal"
self.theme_cls.theme_style = "Dark"

return Builder.load_string(KV)

def toggle_password_visibility(self, text_field):
"""
Toggles the visibility of the password in the given MDTextField.
"""
if text_field.password:
text_field.password = False
text_field.icon_right = "eye-outline" # Change icon to show password
else:
text_field.password = True
text_field.icon_right = "eye-off-outline" # Change icon to hide password

def validate_user(self, username, password):
"""
Validates the username and password entered by the user.
"""

if authenticate(username, password):

self.root.current = "home" # Switch to the HomeScreen
else:
self.root.get_screen("login").ids.result_label.text = "[color=#FF0000]Invalid username or password[/color]"

def logout(self):
"""
Logs the user out and switches back to the LoginScreen.
"""
# Clear the login fields

login_screen = self.root.get_screen("login")

login_screen.ids.username_input.text = ""
login_screen.ids.password_input.text = ""
login_screen.ids.result_label.text = ""

self.root.current = "login" # Switch back to the LoginScreen

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

main.py

Amar kumar Sahu

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Apr 23, 2025, 1:52:32 AMApr 23

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You can diagnose your code and check the logs and errors from AnvPy

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Busola Oronti

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Apr 23, 2025, 7:50:55 AMApr 23

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Thanks very much ElliotG. I'll try the code as edited and revert.

@Amar: thanks for the tool you suggested.

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