Kivy：我想通过单击另一个小部件（例如按钮）来更改小部件的属性（例如文本）

Question

我对 Kivy 完全陌生，想要将屏幕管理器从一个屏幕转换到另一个屏幕。我不知道如何在按钮的 on_press 方法中访问屏幕管理器的属性。

到目前为止，这是我的代码：

from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition
from kivy.uix.button import Button
from kivy.uix.label import Label

class ScreenButton(Button):
    def __init__(self):
        super(Button, self).__init__()
        self.text = "Press Me!"

    def on_press(self, *args):
        sm.current = 'secondscreen'

class MainApp(App):
    def build(self):
        sm = ScreenManager()
        sm.transition = FadeTransition()

        sc1 = Screen(name='firstscreen')
        sc1.add_widget(ScreenButton())

        sc2 = Screen(name='secondscreen')
        sc2.add_widget(Label(text='Another screen!'))

        sm.add_widget(sc1)
        sm.add_widget(sc2)

        return sm

MainApp().run()

我了解，此代码不起作用，因为 sm 未在按钮的方法中定义。但是，例如，如何访问按钮的类定义中的特定小部件？或者有没有更优雅的方式来设置小部件之间的通信以通过彼此改变它们的条件？

感谢您的帮助。

Answer 1

您也可以将 sm (ScreenManager) 作为 kwarg 传递（请参阅###）。这样您就可以重用 ScreenButton 而不必使用全局。

from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition
from kivy.uix.button import Button
from kivy.uix.label import Label

class ScreenButton(Button):

   def __init__(self, **kwargs): ###
       super(ScreenButton, self).__init__()

       self.manager = kwargs.pop('manager', None) ### 
       self.text = "Press Me!"

   def on_press(self, *args):

       self.manager.current = 'secondscreen' ###


class MainApp(App):
    def build(self):

        sm = ScreenManager()

        sm.transition = FadeTransition()

        sc1 = Screen(name='firstscreen')
        sc1.add_widget(ScreenButton(manager=sm)) ###

        sc2 = Screen(name='secondscreen')
        sc2.add_widget(Label(text='Another screen!'))

        sm.add_widget(sc1)
        sm.add_widget(sc2)

        return sm

MainApp().run()

Answer 2

在您的示例中执行此操作的一种方法是将sm 设为全局：

from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition
from kivy.uix.button import Button
from kivy.uix.label import Label

class ScreenButton(Button):
    def __init__(self):
        super(ScreenButton, self).__init__()
        self.text = "Press Me!"

    def on_press(self, *args):
        sm.current = 'secondscreen'


sm = ScreenManager()


class MainApp(App):
    def build(self):
        sm.transition = FadeTransition()

        sc1 = Screen(name='firstscreen')
        sc1.add_widget(ScreenButton())

        sc2 = Screen(name='secondscreen')
        sc2.add_widget(Label(text='Another screen!'))

        sm.add_widget(sc1)
        sm.add_widget(sc2)

        return sm

MainApp().run()

Answer 3

好的，我有一个完全不同的解决方案，而且它需要的工作量要少得多。您将需要 2 个文件，main.py 和screens.kv

这里是 main.py：

import kivy
kivy.require('1.10.0')
from kivy.app import App
from kivy.uix.screenmanager import Screen, ScreenManager, FadeTransition
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.uix.gridlayout import GridLayout

class Manager(ScreenManager):
    pass

class FirstScreen(Screen):
    pass

class SecondScreen(Screen):
    pass

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

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

还有screens.kv：

#: import sm kivy.uix.screenmanager

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

<FirstScreen>
    name: 'First'
    GridLayout:
        Label:
            text: "First Screen"
        Button:
            text: "Press Me!"
            on_release: app.root.current = 'Second'

<SecondScreen>
    name: 'Second'
    GridLayout:
        Label:
            text: "Second Screen"
        Button:
            text: "Press Here!"
            on_release: app.root.current = 'First'

希望这会有所帮助。