How to add an id in Kivy's .kv file?

Question

I'm struggling to come up with a simple example for using IDs. Later I want to use the IDs to change parameters, for instance to change the text in a label or a button. So how do I get started? I can't find simple example for using IDs.

import kivy
from kivy.uix.gridlayout import GridLayout
from kivy.app import App

class TestApp(App):
    pass

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

The .kv file:

#:kivy 1.0

Button:
    text: 'this button \n is the root'
    color: .8, .9, 0, 1
    font_size: 32

    Label: 
        text: 'This is a label'
        color: .9, 0, .5, .5

In this case I would like to use an ID for the label and be able to change the text.

Answer 1

You can find some info about the kv language here . You need to use kivy properties for that.

here is an example on how you can change the label text when you press the button: python file:

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

class GridScreen(GridLayout):
    label = ObjectProperty() #accessing the label in python
    def btnpress(self):
        self.label.text = 'btn pressed' #changing the label text when button is pressed

class TestApp(App):
    def build(self):
        return GridScreen()

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

kv file:

<GridScreen>:
    label: label #referencing the label
    rows: 2
    Button:
        text: 'this button \n is the root'
        color: .8, .9, 0, 1
        font_size: 32
        on_press: root.btnpress() #calling the method 

    Label:
        id: label
        text: 'This is a label'
        color: .9, 0, .5, .5