在 Kivy 中创建全局变量

My code is as follows [PYTHON followed by the KIVY]:

from kivy.app import App
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.accordion import Accordion, AccordionItem
from kivy.uix.boxlayout import BoxLayout 
from kivy.uix.textinput import TextInput
from kivy.uix.label import Label
from kivy.uix.button import Button
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.properties import ObjectProperty



class ScreensManaged(ScreenManager):
    pass

class MainScreen(Screen):
    pass

class SettingsScreen(Screen):
    pass

class StoryScreen(Screen):
    pass

class StoryApp(App):
    def build(self):
        return ScreensManaged()

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

还有……

#:kivy 1.8.0

<ScreensManaged>:
    MainScreen:
    SettingsScreen:

<MainScreen>:
    name: "main"
    FloatLayout:
        Button:
            text: "Begin the story!" 
            size_hint: .25, 0.10
            pos_hint: {'x':.70, 'y':.25}
            on_release: app.root.current = "settings"
        Button:
            text: "Settings"
            size_hint: .25, 0.10
            pos_hint: {'x':.70, 'y': .13}
            on_release: app.root.current = "settings"

<SettingsScreen>:
    name: "settings"
    BoxLayout:
        orientation: "vertical"
        Accordion:
            orientation: "vertical"

            AccordionItem:
                title: "Main Character"
                size_hint:.9, 0.10
                pos_hint: {'x':0.05, 'y':0.85}

                Label:
                    text: "First Name"
                TextInput:
                    id: firstName
                    text: "There's an animal in trouble!"

            AccordionItem:
                title: "Love Interest"
                size_hint: .9, 0.10
                pos_hint: {'x':0.05, 'y':0.70}
        Button:
            text: "What's up"
            on_release: app.root.current = "main"

感兴趣的问题领域:

<StoryScreen>:
     Label:
         text: firstname.text

我知道它不能以这种方式工作，因为小部件的属性仅限于类范围 - 但是当我尝试在 Python 中将 StoryScreen 设为 SettingsScreen 的类时，Kivy 不会打开 - 当我尝试创建一个SettingsScreen 类中的全局变量

class SettingsScreen(Screen):
    global first
    first = self.ids['first name']

class SettingsScreen(Screen):
   first = self.ids['first name']
   global first 

class SettingsScreen(Screen):
    global first
    first = self.ids['first name']