调用一个在kivy的kv语言中不起作用的变量

Question

我的问题是，在我在一个屏幕上设置变量之后如何在另一个屏幕上调用它？

以下是我要做的事情的代码：

main.py

import kivy
kivy.require('1.10.0')
from kivy.app import App
from kivy.uix.screenmanager import Screen, ScreenManager

class Manager(ScreenManager):
    pass

class FirstScreen(Screen):
    pass

class SecondScreen(Screen):
    pass

class ExampleApp(App):
    def build(self):
        return Manager()

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

example.kv

#: import sm kivy.uix.screenmanager
#: set Question 'not working'

<Manager>
    transition: sm.FadeTransition()
    FirstScreen:
    SecondScreen:

<FirstScreen>
    BoxLayout:
        TextInput:
            id: txt
            multiline: False
        Button:
            text: 'Press Me'
            on_release:
                Question = txt.text
                app.root.current = 'Next'

<SecondScreen>
    name: 'Next'
    Label:
        text: Question

当它运行时，一切正常。有一个例外。 SecondScreen上的标签显示＆＃34;不工作＆＃34;何时应该读取我在FirstScreen上的文本输入中键入的内容。为什么我不能完成这项任务？

Answer 1

您必须提供id标记并使用ids方法或ObjectProperty来引用变量。有关详细信息，请参阅下面的两个示例。

示例1 - 使用ID方法

id是小部件的弱参数。

main.py

from kivy.app import App
from kivy.uix.screenmanager import Screen, ScreenManager


class Manager(ScreenManager):
    pass


class FirstScreen(Screen):
    pass


class SecondScreen(Screen):
    pass


class ExampleApp(App):
    def build(self):
        return Manager()


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

example.kv

#:kivy 1.10.0
#:import FadeTransition kivy.uix.screenmanager.FadeTransition
#: set Question 'not working'

<Manager>
    transition: FadeTransition()
    FirstScreen:
    SecondScreen:
        id: second_screen

<FirstScreen>
    BoxLayout:
        TextInput:
            id: txt
            text: "Working!"
            multiline: False
        Button:
            text: 'Press Me'
            on_release:
                root.manager.ids.second_screen.ids.label.text = txt.text
                app.root.current = 'Next'

<SecondScreen>
    name: 'Next'
    Label:
        id: label
        text: Question

输出 - 使用ids方法

示例2 - 使用ObjectProperty

使用ObjectProperty的“最佳实践”。这样可以创建直接引用，提供更快的访问速度，并且更加明确。

main.py

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


class Manager(ScreenManager):
    second_screen = ObjectProperty()


class FirstScreen(Screen):
    pass


class SecondScreen(Screen):
    label = ObjectProperty()


class ObjectPropertyApp(App):
    def build(self):
        return Manager()


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

objectproperty.kv

#:kivy 1.10.0
#:import FadeTransition kivy.uix.screenmanager.FadeTransition
#: set Question 'not working'

<Manager>
    second_screen: second_screen
    transition: FadeTransition()
    FirstScreen:
    SecondScreen:
        id: second_screen

<FirstScreen>
    BoxLayout:
        TextInput:
            id: txt
            text: "Working!"
            multiline: False
        Button:
            text: 'Press Me'
            on_release:
                root.manager.second_screen.label.text = txt.text
                app.root.current = 'Next'

<SecondScreen>
    name: 'Next'
    label: label
    Label:
        id: label
        text: Question

输出 - 使用ObjectProperty