kivy 17 screen manager

#screen.py

from kivy.app import App

from kivy.base import runTouchApp

from kivy.lang import Builder

from kivy.properties import ListProperty

from kivy.uix.boxlayout import BoxLayout

from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition

import time

import random

class FirstScreen(Screen):

    pass

class SecondScreen(Screen):

    pass

class ColourScreen(Screen):

    colour = ListProperty([1, 0, 0, 1])

class MyScreenManager(ScreenManager):

    def new_colour_screen(self):

        name = str(time.time())

        s = ColourScreen(name=name, colour=[random.random() for _ in range(3)] + [1])

        self.add_widget(s)

        self.current = name

root_widget = Builder.load_string('''

#:import FadeTransition kivy.uix.screenmanager.FadeTransition

MyScreenManager:

    transition: FadeTransition()

    FirstScreen:

    SecondScreen:

    

<FirstScreen>

    name: 'first'

    BoxLayout:

        orientation: 'vertical'

        Label:

            text: 'first screen'

            font_size: 30

        Image:

            source: 'img/1.jpg'

            allow_stretch: True

            keep_ratio: False

        BoxLayout:

            Button:

                text: 'goto second screen'

                font_size: 30

                on_release: app.root.current = 'second'

            Button:

                text: 'get random colour screen'

                font_size: 30

                on_release: app.root.new_colour_screen()

<SecondScreen>

    name: 'second'

    BoxLayout:

        orientation: 'vertical'

        Label:

            text: 'second screen'

            font_size: 30

        Image:

            source: 'img/5.jpg'

            allow_stretch: True

            keep_ratio: False

        BoxLayout:

            Button:

                text: 'goto first screen'

                font_size: 30

                on_release: app.root.current = 'first'

            Button:

                text: 'get random colour screen'

                font_size: 30

                on_release: app.root.new_colour_screen()

            

<ColourScreen>:

    BoxLayout:

        orientation: 'vertical'

        Label:

            text: 'colour {:.2},{:.2},{:.2} screen'.format(*root.colour[:3])

            font_size: 30

        Widget:

            canvas:

                Color:

                    rgba: root.colour

                Ellipse:

                    pos: self.pos

                    size: self.size

        BoxLayout:

            Button:

                text: 'goto first screen'

                font_size: 30

                on_release: app.root.current = 'first'

            Button:

                text: 'get random colour screen'

                font_size: 30

                on_release: app.root.new_colour_screen()

''')

class ScreenManagerApp(App):

    def build(self):

        return root_widget

ScreenManagerApp().run()

reference:

https://www.youtube.com/watch?v=xx-NLOg6x8o&list=PLdNh1e1kmiPP4YApJm8ENK2yMlwF1_edq&index=14