Kivy: Retrieving Text from Widget in another Class?

Question

I am trying to access the TextInput.text of one class (here "UserInput") from another class (here "GetInfoFromAnotherClass"). However, the "Retrieve Info" Button only gives the initial Input and does not update. While from within the class "UserInput" it is no problem --> Button "Get Info". Whatever I put into the text fields, the "Retrieve Info"-Button always returns "First Input". I don't know what to google for anymore. Hope, you guys, can help me out!

Here is a "close to minimal" example of my problem:

import kivy
from kivy.app import App
from kivy.properties import ObjectProperty
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.gridlayout import GridLayout


class Container(GridLayout):
    pass

class UserInput(BoxLayout):
    first_input = ObjectProperty(None)
    second_input = ObjectProperty(None)

    def __init__(self,**kwargs):
        super().__init__(**kwargs)

    def ui_btn(self):
        print(self.first_input.text)
        print(self.second_input.text)


class GetInfoFromAnotherClass(BoxLayout):
    def __init__(self,**kwargs):
        super().__init__(**kwargs)
        self.ui = UserInput()

    def retrieve_info(self):
        print(self.ui.first_input.text)
        print(self.ui.second_input.text)


class MainApp(App):
    def build(self):
        return Container()

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

And main.kv:

#:kivy 1.11.0

# Well this is just for Beauty ;-)
<MyTextInput@TextInput>:
    size_hint_y: None
    height: 50
    multiline: False
    write_tab: False

<MyButton@Button>:
    size_hint_y: None
    height: 50

<Container>:

    cols: 1

    UserInput
    GetInfoFromAnotherClass

<UserInput>:
    first_input: first_input
    second_input: second_input
    size_hint_y: None
    height: self.minimum_height
    padding: 20

    MyTextInput:
        id: first_input
        text: "First Entry"

    MyTextInput:
        id: second_input
        text: "Second Entry"

    MyButton:
        text: "Get Info in the same class"
        on_press: root.ui_btn()

<GetInfoFromAnotherClass>:
    size_hint_y: None
    height: self.minimum_height
    padding: 20

    MyButton:
        text: "Retrieve Info from another Class"
        on_press: root.retrieve_info()

Answer 1

The self.ui = UserInput() call creates a different UserInput instance, one that nobody is using.

One way to access the text boxes is this:

• First give your UserInput instance an id

<Container>:
    cols: 1
    UserInput:
        id: user_input_box
    GetInfoFromAnotherClass:

• Create a variable that stores the currently running App

class GetInfoFromAnotherClass(BoxLayout):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.app = App.get_running_app()
        # self.ui = UserInput()

• After that, use the code below to access the texts..

    def retrieve_info(self):
        print(self.app.root.ids.user_input_box.ids.first_input.text)
        print(self.app.root.ids.user_input_box.ids.second_input.text)