kivy:全局变量和ScreenManager

Question

我使用来自First Screen的输入，将该输入存储到全局变量CHOSEN_INPUT中，然后当我转到Second Screen时，该全局变量将显示在那里。

我已经有了开始，但不知道该去哪里。。。也许使用ObjectProperty，但我不知道如何将它从一个类传递到另一个类。

global_test.py

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label
from kivy.uix.button import Button
from kivy.uix.screenmanager import Screen, ScreenManager, NoTransition
from kivy.properties import ObjectProperty

#global variable
CHOSEN_INPUT = ''

class FirstScreen(Screen):
    obj_input = ObjectProperty()
    obj_label = ObjectProperty()
    obj_okay = ObjectProperty()
    def buttonClicked(self):
        global CHOSEN_INPUT
        print('RESULT :', self.obj_input.text)
        self.obj_label.text = "You wrote : " + self.obj_input.text
        CHOSEN_INPUT = self.obj_input.text

class SecondScreen(Screen):
    pass

class FromFirstScreen(BoxLayout):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        global CHOSEN_INPUT
        self.orientation = 'vertical'
        lbl = Label(Text=CHOSEN_INPUT)
        self.add_widget(lbl) 

class Global_VariableApp(App):
    def build(self):
        sm = ScreenManager(transition=NoTransition())
        sm.add_widget(FirstScreen(name='firstcreen'))
        sm.add_widget(SecondScreen(name='secondscreen')) 
        return sm

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

和：

global_variable.kv

<FirstScreen>:
    obj_input: input_box
    obj_label: label_box
    obj_okay: okay_btn
    BoxLayout:
        orientation: 'vertical'
        TextInput:
            id: input_box
            size_hint_y: None
            height: "40dp"
            multiline: False
        Label:
            id: label_box
        Button:
            id: okay_btn
            text: "Okay"
            on_press: root.buttonClicked()
        Button:
            text: "Go To Second Screen"
            on_press: root.manager.current = 'secondscreen' 
<SecondScreen>:
    BoxLayout:
        orientation: 'vertical'
        Button:
            text: "Input from First Screen :"
        FromFirstScreen:
        Button:
            text: "Go To First Screen"
            on_press: root.manager.current = 'firstcreen'

Answer 1

得益于@mcastle的解决方案：从另一个小部件更改Kivy小部件属性

我在类SecondScreen中放入了一个update_text函数：

class SecondScreen(Screen):
    obj_input1_box = ObjectProperty()
    def update_text(self, label_text):
        #print('label_text :', label_text)
        self.obj_input1_box.text = label_text

在kv文件中，我插入了一个函数：root.manager.get_screen('secondscreen').update_text(root.obj_label.text)（并为更新的SecondScreen的文本标签放一个id）：

<FirstScreen>:
    ...
        Button:
            id: okay_btn
            text: "Okay"
            on_press: root.buttonClicked(); root.manager.get_screen('secondscreen').update_text(root.obj_label.text)    ...
<SecondScreen>:
    obj_input1_box: input1_box
    ...
        Label:
            id: input1_box
    ...