当 ScreenManager 位于 Kivy 中的 Widget 的 BoxLayout 内时，尝试在屏幕之间切换

Question

I have a problem, when pressing the button "Next screen", that's not working, and My First Windows is not changing to SecondWindow(Screen)..the app.root.current= 'second' is not working in in the kv.file. And I want to change just the part of the screens(WindowManager:FirstWindow, SecondWindow) and not all MyLayout.. The part of Mylayout have to stay there and just change the screens that those are below of this.

py.file

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.uix.boxlayout import BoxLayout
from kivy.lang import Builder
from kivy.core.spelling import Spelling
from kivy.uix.screenmanager import ScreenManager, Screen


kv= Builder.load_file('test2.kv')

class MyLayout(Widget):
    def spinner_clicked(self,value):
           self.ids.Label1.text= f'You selected: {value}' 



#Definine our different screens
class FirstWindow(Screen):
    pass

class SecondWindow(Screen):
    pass

class WindowManager(ScreenManager):
    pass 


class AwesomeApp(App):
    def build(self):
        return MyLayout()

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

kv.file

<MyLayout>

    BoxLayout:
        orientation:"vertical"
        size: root.width, root.height
        GridLayout:
            cols:3
            rows:3
            

            Spinner:
                id: spinner_id
                text: "Menu"
                values: ["Catalogue","Buy","Payment Methods", "Contact"]
                on_text: root.spinner_clicked(spinner_id.text)

        

            Label:
                id: Label1
                text: "My Panel"

            Button:
                text:"Buy"

    
        #THESE SCREENS ARE NOT CHANGING
        WindowManager:
            FirstWindow:
            SecondWindow:  
    
<FirstWindow>:
    name: "first"
    BoxLayout:
        orientation: "vertical"
        size: root.width, root.height

        Label:
            text: "First Screen"
            font_size: 32

        Button:
            text: "Next Screen"
            font_size: 32
            on_release: 
                app.root.current= "second"
                root.manager.transition.direction= "left" #up

<SecondWindow>:
    name: "second"
    BoxLayout:
        orientation: "vertical"
        size: root.width, root.height

        Label:
            text: "Second Screen"
            font_size: 32

        Button:
            text: "Go Back"
            font_size: 32
            on_release: 
                app.root.current= "first"
                root.manager.transition.direction= "right"

Answer 1

Change your app.root.current references in your kv to root.manager.current as I suggested in your previous question.