My First Kivy App

# не забудь импортировать необходимые элементы!
# Translation:
# Don't forget to import the necessary elements!

from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.button import Button
from kivy.uix.textinput import TextInput
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.scrollview import ScrollView

class ScrButton(Button):
    def __init__(self, screen, direction='right', goal='main', **kwargs):
        super().__init__(**kwargs)
        self.screen = screen
        self.direction = direction
        self.goal = goal
    def on_press(self):
        self.screen.manager.transition.direction = self.direction
        self.screen.manager.current = self.goal

class MainScr(Screen):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        vl = BoxLayout(orientation='vertical', padding=8, spacing=8)
        hl = BoxLayout()
        txt = Label(text= 'Choose a screen')
        vl.add_widget(ScrButton(self, direction='down', goal='first', text="1"))
        vl.add_widget(ScrButton(self, direction='left', goal='second', text="2"))
        vl.add_widget(ScrButton(self, direction='up', goal='third', text="3"))
        vl.add_widget(ScrButton(self, direction='right', goal='fourth', text="4"))
        hl.add_widget(txt)
        hl.add_widget(vl)
        self.add_widget(hl)

class FirstScr(Screen):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        vl = BoxLayout(orientation='vertical', size_hint=(.5, .5), pos_hint={'center_x': 0.5, 'center_y': 0.5})
        btn = Button(text= 'Choice: 1', size_hint=(.5, 1), pos_hint={'left': 0})
        btn_back = ScrButton(self, direction='up', goal='main', text="Back", size_hint=(.5, 1), pos_hint={'right': 1})
        vl.add_widget(btn)
        vl.add_widget(btn_back)
        self.add_widget(vl)

# WE STOPPED HERE (26th February 2023)
class SecondScr(Screen):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        vl = BoxLayout(orientation='vertical')
        self.txt = Label(text= 'Choice: 2')
        vl.add_widget(self.txt)

        hl_0 = BoxLayout(size_hint=(0.8, None), height='30sp')
        lbl1 = Label(text='Enter password:', halign='right')
        self.input = TextInput(multiline=False)

        hl_0.add_widget(lbl1)
        hl_0.add_widget(self.input)
        vl.add_widget(hl_0)

        hl = BoxLayout(size_hint=(0.5, 0.2), pos_hint={'center_x': 0.5})
        btn_false = Button(text="OK!")
        btn_back = ScrButton(self, direction='right', goal='main', text="Back")

        hl.add_widget(btn_false)
        hl.add_widget(btn_back)
        vl.add_widget(hl)
        self.add_widget(vl)
        btn_false.on_press = self.change_text

    def change_text(self):
        self.txt.text = self.input.text + "? Didn't work ..."

# SCREEN THREE HAS A BUTTON AND A LABEL
class ThirdScr(Screen):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        layout = BoxLayout(orientation='vertical')
        btn_back = ScrButton(self, direction='down', goal='main', text="Back", size_hint=(1, None), height='40sp')
        test_label = Label(text = "Your own screen")
        layout.add_widget(test_label)
        layout.add_widget(btn_back)
        self.add_widget(layout)

# SCREEN FOUR HAS SCROLLING ENABLED!
class FourthScr(Screen):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        vl = BoxLayout(orientation='vertical', spacing=8)
        a = 'START ' + 'Choice: 3 ' * 200
        test_label = Label(text = "Extra exercise",size_hint=(0.3,None))

        btn_back = ScrButton(self, direction='left', goal='main', text="Back", size_hint=(1, .2), pos_hint={'center-x': 0.5})
        self.label = Label(text=a, size_hint_y=None, font_size='24sp', halign='left', valign='top')
        self.label.bind(size=self.resize)

        self.scroll = ScrollView(size_hint=(1, 1))
        self.scroll.add_widget(self.label)

        vl.add_widget(test_label)
        vl.add_widget(btn_back)
        vl.add_widget(self.scroll)
        self.add_widget(vl)

    def resize(self, *args):
        self.label.text_size = (self.label.width, None)
        self.label.texture_update()
        self.label.height = self.label.texture_size[1]

class MyApp(App):
    def build(self):
        sm = ScreenManager()
        sm.add_widget(MainScr(name='main'))
        sm.add_widget(FirstScr(name='first'))
        sm.add_widget(SecondScr(name='second'))
        sm.add_widget(ThirdScr(name='third'))
        sm.add_widget(FourthScr(name='fourth'))
        return sm

MyApp().run()