Develop Reference

Why my ScreenManager not switching in Kivy

I'm trying to build an interface in python with Kivy. To do this, i want to follow this structure:
[ScreenManager#1] -> [Login Screen]
[ScreenManager#2] -> [All others screens]
My ScreenManager#1 is declared in my App function in python file. My ScreenManager#2 is initialised in a kv file. To simply the help that you can bring to me, i've joined the two in the code below.
my AllScreensScreenManager#2, need to have a template shared with all the other screens. I've gave an id to it and call this one with my button in my LoginScreen, like this was suggested here. But the switch is not working. What i'm doing wrong with it.
import kivy
kivy.require('2.1.0') # replace with your current kivy version !
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager,Screen
Builder.load_string('''
<AllScreens>:
id: second_manager
manager: scr_manager
orientation: "vertical"
BoxLayout:
ScreenManager:
id: scr_manager
transition: "left"
Welcome:
GenerateScreen:
ModifyScreen:
ConsultScreen:
LogoutScreen:
BoxLayout:
size_hint: 1, None
height: "40dp"
pos_hint: {"bottom": 0}
spacing: "5dp"
Button:
id: consult
text: "Consult"
on_press: root.manager.current("consult")
Button:
id: modify
text: "Modify"
on_press: root.manager.current("modify")
Button:
id: generate
text: "Generate"
on_press: root.manager.current("generate")
Button:
id: logout
text: "Logout"
on_press: root.manager.current("logout")
<LoginScreen>:
name: "login"
BoxLayout:
Label:
text: "Login"
Button:
text: "Connect"
on_release: second_manager.current("welcome")
<WelcomeScreen>:
name: "welcome"
BoxLayout:
Label:
text: "welcome"
<ConsultScreen>:
name: "consult"
BoxLayout:
Label:
text: "consult"
<GenerateScreen>:
name: "generate"
BoxLayout:
Label:
text: "password"
''')
class ScreenManagement(ScreenManager):
pass
class LoginScreen(Screen):
print("login screen")
pass
class WelcomeScreen(Screen):
pass
class AllScreens(ScreenManager):
pass
class ConsultScreen(Screen):
pass
class GenerateScreen(Screen):
pass
class MyApp(App):
def build(self):
sm = ScreenManagement()
sm.add_widget(LoginScreen(name="login"))
return sm
if __name__ == '__main__':
MyApp().run()

How do I pass an argument between KivyMD screens?

When going from the first screen to the second screen, I want to pass a variable as an argument so that kivyMD can update the second screen from text stored in an excel file. The following is a skeleton of my app's functionality:
The user reaches Screen 1 thru the navigation drawer in KivyMD, screen 1 presents the user with two options on two small clickable MDCards:
"Change text to 1"
"Change text to 2"
After clicking on one of these, the app switches to screen 2 with a single big MDCard, the text on this MDCard should change to reflect the option the user chose.
However, kivy is pulling the text that is to be displayed on the big MDCard from an excel file.
The variable that I want to pass from screen 1 to screen 2 is simply a number (1 or 2) that will tell kivy which row in the excel file it should pull the text from
If the user clicks "Change text to 1" then the first screen should pass "1" as the argument row_x to the function def change_text() (see screen 2 .py) so that the text in row 1 of excel can be displayed on the second screen. How can I achieve this?
I have 4 files in total; 3 are .py files (one for the main app, one for screen 1, and one for screen 2), and the excel file
NOTE: in the code below, Screen 1 & 2 are called Element 1 & 2 respectfully
Main.py:
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
from kivy.properties import ObjectProperty
from kivymd.app import MDApp
from element_1 import element_1_screen
from element_2 import element_2_screen
MainNavigation = '''
<ContentNavigationDrawer>:
ScrollView:
MDList:
OneLineListItem:
text: 'Go to Element 1'
on_press:
root.nav_drawer.set_state("close")
root.screen_manager.current = "go_to_element_1_screen"
Screen:
MDToolbar:
id: toolbar
pos_hint: {"top": 1}
elevation: 10
left_action_items: [["menu", lambda x: nav_drawer.set_state("open")]]
MDNavigationLayout:
x: toolbar.height
ScreenManager:
id: screen_manager
Screen:
name: "words_nav_item"
element_1_screen:
name: "go_to_element_1_screen"
element_2_screen:
name: "go_to_element_2_screen"
MDNavigationDrawer:
id: nav_drawer
ContentNavigationDrawer:
screen_manager: screen_manager
nav_drawer: nav_drawer
'''
class ContentNavigationDrawer(BoxLayout):
screen_manager = ObjectProperty()
nav_drawer = ObjectProperty()
class mainApp(MDApp):
def build(self):
self.theme_cls.primary_palette = "Red"
return Builder.load_string(MainNavigation)
mainApp().run()
Screen 1 / Element 1
from kivy.lang import Builder
from kivymd.uix.screen import MDScreen
element_1_contents = '''
<element_1_screen>:
MDGridLayout:
rows: 2
size: root.width, root.height
pos_hint: {"center_x": .8, "center_y": .2}
spacing: 40
MDCard:
orientation: 'vertical'
size_hint: None, None
size: "360dp", "120dp"
ripple_behavior: True
on_release:
root.manager.current = "go_to_element_2_screen"
MDLabel:
id: LabelTextID
text: "Change Text to 1"
halign: 'center'
MDCard:
orientation: 'vertical'
size_hint: None, None
size: "360dp", "120dp"
ripple_behavior: True
on_release:
root.manager.current = "go_to_element_2_screen"
MDLabel:
id: LabelTextID
text: "Change Text to 2"
halign: 'center'
'''
class element_1_screen(MDScreen):
def __init__(self, **kwargs):
super().__init__(**kwargs)
Builder.load_string(element_1_contents)
Screen 2 / Element 2
from kivy.lang import Builder
from kivymd.uix.screen import MDScreen
import openpyxl
element_2_contents = '''
<element_2_screen>:
MDCard:
orientation: 'vertical'
size_hint: None, None
size: "360dp", "360dp"
pos_hint: {"center_x": .5, "center_y": .5}
ripple_behavior: True
focus_behavior: True
on_release: root.manager.current = "go_to_element_1_screen"
MDLabel:
id: TextID
text: "NOTHING HAS CHANGED"
halign: 'center'
MDLabel:
text: "(Click here to return)"
halign: 'center'
'''
class element_2_screen(MDScreen):
def __init__(self, **kwargs):
super().__init__(**kwargs)
path = "data.xlsx"
self.wb_obj = openpyxl.load_workbook(path)
self.sheet_obj = self.wb_obj.active
Builder.load_string(element_2_contents)
def change_text(self, row_x=0):
row_number = self.sheet_obj.cell(row_x, column=1)
self.ids.TextID.text = str(row_number.value)
And the excel file only has two entries in Column A:
Row 1: You have chosen 1
Row 2: You have chosen 2

I found the answer and now it works flawlessly. Someone over on Reddit (u/Username_RANDINT) helped me, this is what they said:
The ScreenManager has a get_screen() method. You could use it to get
the instance of the second screen and call the change_text() method on
that. In the same place where you switch screens, add another line:
on_release:
root.manager.current = "go_to_element_2_screen"
root.manager.get_screen("go_to_element_2_screen").change_text(1)
Then the same for the other card, just pass in 2 instead of 1.

Kivy Python: buttons and classes for multiple screens

I have a problem with my Kivy Python Code. I have 2 screens: 1st is to navigate to the second screen and on the 2nd screen there is a button to add text to a scrollview...navigating is working but it does not add any text to the scrollview...I think I need some help here! AttributeError: 'super' object has no attribute 'getattr'
import kivy
from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.gridlayout import GridLayout
from kivy.uix.textinput import TextInput
from kivy.uix.button import Button
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.clock import Clock, mainthread
from kivy.core.window import Window
from kivy.uix.scrollview import ScrollView
from kivy.effects.scroll import ScrollEffect
from kivy.lang import Builder
Builder.load_string("""
<MenuScreen>:
name: 'mainmenu'
BoxLayout:
spacing: 1
orientation: "vertical"
Label:
text: "MAIN MENU"
Button:
text: 'Go to Screen 2'
on_release:
root.manager.current = 'screen2'
root.manager.transition.direction = "left"
Button:
text: 'Quit'
on_release: root.manager.current = app.exit_software()
<Screen2>:
name: 'screen2'
BoxLayout:
spacing: 1
orientation: "vertical"
ScrollView:
id: scroll_view
always_overscroll: False
BoxLayout:
size_hint_y: None
height: self.minimum_height
orientation: 'vertical'
Label:
id: label
text: "You can add some Text here by pressing the button"
size_hint: None, None
size: self.texture_size
Button:
text: 'Add text!'
size_hint_y: 0.1
on_release: app.add_text()
Button:
text: 'Back to main menu'
size_hint_y: 0.1
on_release:
root.manager.current = 'mainmenu'
root.manager.transition.direction = "right"
""")
# Declare both screens
class MenuScreen(Screen):
pass
class Screen2(Screen):
pass
class AddTextApp(App):
def __init__(self,**kwargs):
super().__init__(**kwargs)
def build(self):
# Create the screen manager
sm = ScreenManager()
sm.add_widget(MenuScreen(name='mainmenu'))
sm.add_widget(Screen2(name='screen2'))
return sm
def add_text(self):
self.root.ids.label.text += f"Some new Text\n"
self.root.ids.scroll_view.scroll_y = 0
def exit_software(self):
App.get_running_app().stop()
if __name__ == '__main__':
AddTextApp().run()
Thank you very much in advance!

The error occurred because self.root.ids gets access to widgets located in the root widget of the main class. To access the secondary screen elements, you need to add it to the main class (in your case, in ScreenManager) and set its id. Also, you have a lot of imported excess, so that it is clearly visible, I advise you to use Pycharm or something like that.
from kivy.app import App
from kivy.uix.screenmanager import Screen
from kivy.lang import Builder
kv = """
<MenuScreen>:
name: 'mainmenu'
BoxLayout:
spacing: 1
orientation: "vertical"
Label:
text: "MAIN MENU"
Button:
text: 'Go to Screen 2'
on_release:
root.manager.current = 'screen2'
root.manager.transition.direction = "left"
Button:
text: 'Quit'
on_release: root.manager.current = app.exit_software()
<Screen2>:
name: 'screen2'
BoxLayout:
spacing: 1
orientation: "vertical"
ScrollView:
id: scroll_view
always_overscroll: False
BoxLayout:
size_hint_y: None
height: self.minimum_height
orientation: 'vertical'
Label:
id: label
text: "You can add some Text here by pressing the button"
size_hint: None, None
size: self.texture_size
Button:
text: 'Add text!'
size_hint_y: 0.1
on_release: app.add_text()
Button:
text: 'Back to main menu'
size_hint_y: 0.1
on_release:
root.manager.current = 'mainmenu'
root.manager.transition.direction = "right"
ScreenManager:
MenuScreen:
id: menu_scr
Screen2:
id: scr_2
"""
class MenuScreen(Screen):
pass
class Screen2(Screen):
pass
class AddTextApp(App):
def __init__(self, **kwargs):
super().__init__(**kwargs)
def build(self):
return Builder.load_string(kv)
def add_text(self):
self.root.ids.scr_2.ids.label.text += f"Some new Text\n"
self.root.ids.scr_2.ids.scroll_view.scroll_y = 0
#staticmethod
def exit_software():
App.get_running_app().stop()
if __name__ == '__main__':
AddTextApp().run()

Only "else statement" shown when running app with python/kivy

I have been working on an app with Kivy that receives 0, 1 or 2 as text input by the user and a label on the final screen shows a text which should differ based on the received input. It does not present with any errors any longer, but the final screen will only show the "else" text ("Bad Luck") even when the requirements of the "if statement" are met.
By searching similar questions, I tried using an "input_filter" for integers in case it resolved the issue, but it didn't.
I am a beginner with no programming background, so please feel free to be as elaborate as you like in your answers. Thank you in advance for your time and any ideas/recommendations you may share. Following are the codes of the .py and .kv files:
.py file:
import kivy
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.label import Label
from kivy.uix.gridlayout import GridLayout
from kivy.uix.textinput import TextInput
from kivy.uix.button import Button
from kivy.uix.widget import Widget
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.properties import NumericProperty, StringProperty, NumericProperty
class MainWindow(Screen):
pass
class SecondWindow(Screen):
pass
class ThirdWindow(Screen):
pass
class FourthWindow(Screen):
pass
class WindowManager(ScreenManager):
pass
class MyApp(App):
def build(self):
kv = Builder.load_file("my.kv")
return kv
if __name__=="__main__":
MyApp().run()
.kv file:
WindowManager:
MainWindow:
SecondWindow:
ThirdWindow:
FourthWindow:
<MainWindow>:
name: "main"
GridLayout:
cols:1
rows:2
Label:
text: "stuff"
Button:
text: "stuff"
on_release:
app.root.current = "second"
root.manager.transition.direction = "left"
<SecondWindow>:
name: "second"
GridLayout:
cols:1
rows:2
GridLayout:
cols:2
Label:
text: "stuff"
TextInput:
id: ti_a
multiline:False
Label:
text: "stuff"
TextInput:
id: ti_b
multiline:False
Label:
text: "stuff"
TextInput:
id: ti_c
multiline:False
Label:
text: "stuff"
TextInput:
id: ti_d
multiline:False
Label:
text: "stuff"
TextInput:
id: ti_e
multiline:False
GridLayout:
cols:2
Button:
text: "stuff"
on_release:
app.root.current = "third"
root.manager.transition.direction = "left"
Button:
text: "Back"
on_release:
app.root.current = "main"
root.manager.transition.direction = "right"
<ThirdWindow>:
name: "third"
GridLayout:
cols:1
rows:2
GridLayout:
cols:2
Label:
text: "stuff"
TextInput:
id: ti_f
multiline:False
GridLayout:
cols:2
Button:
text: "stuff"
on_release:
app.root.current = "fourth"
root.manager.transition.direction = "left"
Button:
text: "Back"
on_release:
app.root.current = "second"
root.manager.transition.direction = "right"
<FourthWindow>:
name: "fourth"
Label:
text: "Stuff" if root.manager.get_screen("second").ids.ti_a.text == "0" and root.manager.get_screen("second").ids.ti_b.text == "0" and root.manager.get_screen("second").ids.ti_c.text == "0" and root.manager.get_screen("second").ids.ti_d.text == "0" and root.manager.get_screen("second").ids.ti_e.text == "1" and root.manager.get_screen("third").ids.ti_f.text == "0" else "Bad Luck"

The problem is that kivy doesn't recognize the expression:
root.manager.get_screen("second").ids.ti_a.text
as a property that it can bind to, so the value of Label text in your FourthWindow is only evaluated once (when the FourthWindow is created). Any changes to the other Labels in your app will have no effect on FourthWindow. See the documentation.
The fix is to write your own code to update that Label by adding an id to that Label:
<FourthWindow>:
name: "fourth"
Label:
id: lab
text: ""
And adding a on_pre_enter() method to FourthWindow:
class FourthWindow(Screen):
def on_pre_enter(self, *args):
if self.manager.get_screen("second").ids.ti_a.text == "0" and \
self.manager.get_screen("second").ids.ti_b.text == "0" and \
self.manager.get_screen("second").ids.ti_c.text == "0" and \
self.manager.get_screen("second").ids.ti_d.text == "0" and \
self.manager.get_screen("second").ids.ti_e.text == "1" and \
self.manager.get_screen("third").ids.ti_f.text == "0":
self.ids.lab.text = 'Stuff'
else:
self.ids.lab.text = 'Bad Luck'
This will evaluate your expression and set the text each time just before the FourthWindow is displayed.

kivymd refences with ids

I'm trying to use the id function to reference text_input from MDTextField, however I can't understand how does the id function works. Does anyone know what is wrong in my code?
The first code is the Main App and the second one is where all the widgets are. I've already searched for a solution in internet, but I can't understand why my code does not work.
from kivy.lang import Builder
from kivymd.app import MDApp
from kivy.uix.screenmanager import Screen, ScreenManager
from Screen_helper import Home
class MenuScreen(Screen):
pass
class ProfileScreen(Screen):
pass
sm = ScreenManager()
sm.add_widget(MenuScreen(name='Menu'))
sm.add_widget(MenuScreen(name='Profile'))
class Mainapp(MDApp):
def build(self):
screen = Screen()
helper = Builder.load_string(Home)
screen.add_widget(helper)
key = self.root.ids.username_input
return screen
Mainapp().run()
Home = '''
ScreenManager:
MenuScreen:
ProfileScreen:
<MenuScreen>:
name: 'Menu'
MDRectangleFlatButton:
id: my_button
text: 'Profile'
pos_hint: {'center_x': 0.5, 'center_y': 0.1}
on_press: root.manager.current = 'Profile'
MDTextField:
id: username_input
input_filter: "int"
hint_text: 'CHIAVE NUMERICA'
helper_text: 'compresa tra 0 e 95'
helper_text_mode: 'on_focus'
icon_right: 'key-variant'
icon_right_color: app.theme_cls.primary_color
pos_hint: {'center_x':0.5,'center_y':0.55}
size_hint_x:None
width:230
input_filter: 'int'
<ProfileScreen>:
name: 'Profile'
MDLabel:
text: 'Welcome'
halign: 'center'
MDRectangleFlatButton:
text: 'back'
pos_hint: {'center_x': 0.5, 'center_y': 0.3}
on_press: root.manager.current = 'Menu' '''

Give an id to the MenuScreen class and then access to the widget.
Add this to the kv file.
<MenuScreen>:
id: menu
To access the widget you can now do this in python:
key = self.root.menu.ids.username_input