How to get field value from another screen?

Question

I have a field in the TokenScreen , and I have a MDList in the ListScreen. The problem is , that I can't find a way to get a value from the field in the TokenScreen , and pass it to the ListScreen class , in order to fill the container with widgets. I tried to use init , but it is not possible.

It should get text value from the MDField and pass it to the g = Github(TOKEN)

py file :

class passVarClass():
    def __init__(self):
        self.tokenPassVar = ""


class MainApp(MDApp):
    screen = Screen()

    def build(self):
        self.theme_cls.primary_palette = 'Blue'
        screen = Builder.load_file('layout.kv')
        return screen

    def set_screen(self, screen):
        self.root.current = screen
        print("switching screen to tokenscreen")


class TokenScreen(Screen):
    def on_pre_leave(self, *args):
        objectPass = passVarClass()

        objectPass.tokenPassVar = self.ids.tokenFieldID.text
        print(objectPass.tokenPassVar + "test_tokenClass")

    # pass


class ListScreen(Screen):
    def on_pre_enter(self, *args):

        objectPass = passVarClass()

        g = Github(objectPass.tokenPassVar)
        user = g.get_user()
        repos = user.get_repos()
        for x in repos:
            if x.language is not None:
                self.ids.container.add_widget(
                    TwoLineListItem(text=x.name, secondary_text=x.language)
                )

        pass


class RepoScreen(Screen):
    pass


sm = ScreenManager()
sm.add_widget(TokenScreen(name='tokenscreen'))
sm.add_widget(ListScreen(name='listscreen'))
sm.add_widget(RepoScreen(name='reposcreen'))

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

kv file:

ScreenManager:
    id:scr_mngr
    TokenScreen:
    ListScreen:
    RepoScreen:

<TokenScreen>:
    id:tokenscreenID
    name:'tokenscreen'
    MDToolbar:
        id:toolbarID
        title:"TokenScreen"
        md_bg_color: app.theme_cls.primary_color
        elevation : 10
        left_action_items : [["arrow-left",lambda x: x]]
        pos_hint:{"top":1}
    MDTextFieldRound:
        id:tokenFieldID
        name:"tokenFieldName"
        hint_text:"token"
        mode:"rectangle"
        pos_hint: {'center_x':0.5,'center_y':0.6}
        size_hint_x:None
        width:250
    MDRectangleFlatButton:
        text:"test"
        pos_hint:{'center_x':0.5,'center_y':0.5}
        on_press: root.manager.current = 'listscreen'
        on_press:print("Switching to listscreen")
<ListScreen>:
    id:listScreenID
    name:'listscreen'
    BoxLayout:
        orientation: 'vertical'
    MDToolbar:
        id:toolbarID
        title:"ListScreen"
        md_bg_color: app.theme_cls.primary_color
        elevation : 10
        left_action_items : [["arrow-left",lambda x: app.set_screen("tokenscreen")]]
        pos_hint:{"top":1}
    ScrollView:
        y: -toolbarID.height
        MDList:
            id:container
<RepoScreen>:
    id:repoScreenID
    name:'reposcreen'

Answer 1

you must define a property. Read this source first:

https://kivy.org/doc/stable/api-kivy.properties.html

and This is a simple example of a property definition:

.kv

Manager:
    mgr: sc_mgr
    Main:
        id: sc_mgr
    About:

<MyPaintWidget>:
    on_touch_down: self.on_touch_down
    on_touch_move: self.on_touch_move

<Main>:
    name: "main"
    draw: main_draw
    BoxLayout:
        orientation: "vertical"

        MyPaintWidget:
            id: main_draw
            size_hint: 1, 0.9

        GridLayout:
            size_hint: 1, 0.1
            cols: 3
            padding: 10

            Button:
                text: "About"
                on_press:
                    root.manager.current= "about"
                    root.manager.transition.direction= "left"
            Label:
            
            Button:
                text: "Clear"
                on_release: app.root.cleaner()

<About>:
    name: "about"
    BoxLayout:
        orientation: "vertical"
        padding: 10

        Label:
            size_hint: 1, 0.9
            text: "This is a test app."

        Button:
            size_hint: 1, 0.9
            text:"Back to Main"
            on_press:
                root.manager.current= "main"
                root.manager.transition.direction= "right"

.py

from random import random
from kivy.app import App
from kivy.uix.widget import Widget
from kivy.graphics import Ellipse, Color, Line
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.lang import Builder
from kivy.properties import ObjectProperty

class Main(Screen):
    draw = ObjectProperty(None)

class About(Screen):
    pass

class Manager(ScreenManager):
    mgr = ObjectProperty(None)

    def cleaner(self):
        self.mgr.draw.clean()


class MyPaintWidget(Widget):

    def clean(self):
        self.canvas.clear()
    
    def on_touch_down(self, touch):
        # self.rect.pos = touch.pos
        color = (random(),random(),random())
        with self.canvas:
            Color(*color)
            Ellipse(pos=(touch.x, touch.y), size=(20,20))
            touch.ud['line'] = Line(points=(touch.x, touch.y))

    def on_touch_move(self, touch):
        # self.rect.pos = touch.pos
        touch.ud['line'].points += [touch.x, touch.y]
        

main_style = Builder.load_file("ms_paint.kv")

class MyPaintApp(App):
    def build(self):
        return main_style


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