通过py文件访问在kv文件中创建的kivy屏幕管理器

Question

i want to create the ScreenManager in the kv file, but i also need th change the shown screen in the .py file. Thats because i have to create some buttons
dynamically and bind a specific function to them, which will change to a specific (button related) screen. Creating the buttons is way more convient in python. So the main question is: how to access the screenmanager created in a kv file through the py file? To explain it a bit futher, here is some code:

kv file

#: kivy 1.10.1

ScreenManager:
    id: screen_manager

    FirstScreen:
        id: first_screen
        name: 'FirstScreen'
        manager: 'screen_manager'
    SecondScreen:
        id: second_screen
        name: 'SecondScreen'
        manager: 'screen_manager'

py file

from kivy.modules import console
from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition
from kivy.properties import ObjectProperty


class FirstScreen(Screen):
    MenuScreen = ObjectProperty(None)

    def SwitchToSecond(self):
        print(ScreenManagement.current)
        ScreenManagement.current = "TestScreen"


class SecondScreen(Screen):
    pass


class testApp(App):
    pass

if __name__ == "__main__":
    testApp().run()

thank you for any guidance in advance

Answer 1

Here is a simple example using the ScreenManager (I also added a method inside of the MyScreenManager class that accepts a value , which would correspond to the name of the screen you would like to change to, but not necessary for this app to run):

Python

import kivy
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition

class Screen1(Screen):

    pass

class Screen2(Screen):

    pass

class Screen3(Screen):

    pass

class MyScreenManager(ScreenManager):

    def changescreen(self, value):

        self.current = value

#Main application
class TestApp(App):

    def build(self):
        self.sm = MyScreenManager()
        return self.sm

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

kv

<MyScreenManager>:

    Screen1:
        name: 'screen1'
    Screen2:
        name: 'screen2'
    Screen3:
        name: 'screen3'

<Screen1>:

    GridLayout:

        rows: 2
        padding: 20
        spacing: 20

        Button:
            text: 'Go to Screen 2'
            on_press: root.manager.current = 'screen2'

        Button:
            text: 'Go to Screen 3'
            on_press: root.manager.current = 'screen3'

        Label:
            text: 'You are on ' + root.name

<Screen2>:

    GridLayout:

        rows: 2
        padding: 20
        spacing: 20

        Button:
            text: 'Go to Screen 1'
            on_press: root.manager.current = 'screen1'

        Button:
            text: 'Go to Screen 3'
            on_press: root.manager.current = 'screen3'

        Label:
            text: 'You are on ' + root.name

<Screen3>:

    GridLayout:

        rows: 2
        padding: 20
        spacing: 20

        Button:
            text: 'Go to Screen 1'
            on_press: root.manager.current = 'screen1'

        Button:
            text: 'Go to Screen 2'
            on_press: root.manager.current = 'screen2'

        Label:
            text: 'You are on ' + root.name

Answer 2

If you want to access the ScreenManager within a Screen you must use its manager attribute, but for this you must not create a property with the same name, in your case you are doing it which is considered a bad practice.

Modifying your code and adding some elements we obtain the following example:

*.kv

#: kivy 1.10.1

ScreenManager:
    id: screen_manager

    FirstScreen:
        id: first_screen
        name: 'FirstScreen'
        Button:
            text: "First"
            on_press: first_screen.SwitchToSecond()
    SecondScreen:
        id: second_screen
        name: 'SecondScreen'
        Label:
            text: "second"

.*py

from kivy.modules import console
from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition
from kivy.properties import ObjectProperty


class FirstScreen(Screen):
    MenuScreen = ObjectProperty(None)

    def SwitchToSecond(self):
        self.manager.current = "SecondScreen"


class SecondScreen(Screen):
    pass


class testApp(App):
    pass

if __name__ == "__main__":
    testApp().run()