Python | Switch widget in Kivy using .kv file

Kivy is a platform independent GUI tool in Python. As it can be run on Android, IOS, linux and Windows etc. It is basically used to develop the Android application, but it does not mean that it can not be used on Desktops applications.

???????? Kivy Tutorial – Learn Kivy with Examples.

Switch widget:

The Switch widget is active or inactive, as a mechanical light switch. The user can swipe to the left/right to activate/deactivate it. 
The value represented by the switch is either True or False. That is the switch can be either in On position or Off position.
To work with Switch you must have to import: 

from kivy.uix.switch import Switch

Attaching Callback to Switch:

• A switch can be attached with a call back to retrieve the value of the switch.
• The state transition of a switch is from either ON to OFF or OFF to ON.
• When switch makes any transition the callback is triggered and new state can be retrieved i.e came and any other action can be taken based on the state.
• By default, the representation of the widget is static. The minimum size required is 83*32 pixels.
• The entire widget is active, not just the part with graphics. As long as you swipe over the widget’s bounding box, it will work.

Basic Approach:

1) import kivy
2) import kivyApp
3) import Switch
4) import Gridlayout
5) import Label
6) Set minimum version(optional)
7) create Layout class(In this you create a switch):
        --> define the callback of the switch in this
8) create App class
9) create .kv file (name same as the app class):
        1) create boxLayout
        2) Give Label
        3) Create Switch
        4) Bind a callback if needed
10) return Layout/widget/Class(according to requirement)
11) Run an instance of the class

Below is the Implementation:
We have explained how to create button, attach a callback to it and how to disable a button after making it active/inactive.
main.py file:

Python3

# Program to explain how switch works

# import kivy module
import kivy

# base Class of your App inherits from the App class.
# app:always refers to the instance of your application
from kivy.app import App

# this restrict the kivy version i.e
# below this kivy version you cannot
# use the app or software
kivy.require('1.9.0')

# The Switch widget is active or inactive
# The state transition of a switch is from
# either on to off or off to on.
from kivy.uix.switch import Switch

# The GridLayout arranges children in a matrix.
# It takes the available space and
# divides it into columns and rows,
# then adds widgets to the resulting “cells”.
from kivy.uix.gridlayout import GridLayout

# The Label widget is for rendering text.
from kivy.uix.label import Label

# A Gridlayout with a label a switch
# A class which contains all stuff about the switch
class SimpleSwitch(GridLayout):

    # number of rows
    rows = 4

    # Callback for the switch state transition
    # Defining a Callback function
    # Contains Two parameter switchObject, switchValue
    def switch_callback(self, switchObject, switchValue):

        # Switch value are True and False
        if(switchValue):
            print('Switch is ON:):):)')
        else:
            print('Switch is OFF:(:(:(')


# Defining the App Class
class SwitchApp(App):
     # define build function
     def build(self):
          # return the switch class
          return SimpleSwitch()


# Run the kivy app
if __name__ == '__main__':
     SwitchApp().run()

.kv file : in this we have done the callbacks and done the button disable also.

Python3

# .kv file in which the whole functions of a switch
# Along with labels are present

<SimpleSwitch>:

    # creating box layout for better view
    BoxLayout:
        size_hint_y: None
        height: '48dp'

        # Adding label to switch
        Label:
            text: 'Switch normal'

        # creating the switch
        Switch:

            # False means OFF and True means ON
            active: False

            # Arranging a callback to the switch
            on_active: root.switch_callback(self, self.active)

    # Another for another switch

    BoxLayout:
        size_hint_y: None
        height: '48dp'

        Label:
            text: 'Switch active'
        Switch:
            active: True
            on_active: root.switch_callback(self, self.active)


    BoxLayout:
        size_hint_y: None
        height: '48dp'

        Label:
            text: 'Switch off & disabled'

        Switch:
            # disabled True means After making switch False
            # it is disabled now you cannot change its state
            disabled: True
            active: False

    BoxLayout:
        size_hint_y: None
        height: '48dp'

        Label:
            text: 'Switch on & disabled'
        Switch:
            disabled: True
            active: True

Output:
Image 1: 

Image 2: 

Image to show callbacks: