跨屏幕的 Kivy 引用

Question

我想从其他根小部件访问根小部件 ID，但我似乎无法完全掌握在 Kivy 中引用的工作原理，并且使用具有不同屏幕的 ScreenManager 对我来说更加困难。

我想实现以下目标：

编辑：单个文件版本

(这段代码假设你要构建一个复杂的应用程序，所以我不想在启动时加载所有代码。因此在切换屏幕时加载kv_strings，而不是放入ScreenManager的kv代码中。代码基于 Kivy Showcase。）

代码 main.py，编辑 2：工作代码（查看答案原因）

#!/usr/bin/kivy
# -*- coding: utf-8 -*-

from kivy.app import App
from kivy.uix.screenmanager import Screen
from kivy.uix.boxlayout import BoxLayout
from kivy.lang import Builder
from kivy.clock import Clock
from kivy.properties import StringProperty, ObjectProperty


kv_foo = '''
<FooScreen>:
    id: fooscreen_id

    BoxLayout:
        id: content
        orientation: 'vertical'
        spacing: '20dp'
        padding: '8dp'
        size_hint: (1, 1)

BoxLayout:
    orientation: 'vertical'

    Label:
        id: important_text
        size_hint_y: 0.3
        text: app.imp_text

    Button:
        id: magic_change
        size_hint_y: 0.3
        text: "Change text above to text below (after screen switch)"
        on_press: app.change_text()

    ScreenManager:
        id: sm
        on_current_screen:
            idx = app.screen_names.index(args[1].name)
'''


class FooScreen(Screen):
    # 'content' refers to the id of the BoxLayout in FooScreen in foo.kv
    def add_widget(self, *args):
        if 'content' in self.ids:
            return self.ids.content.add_widget(*args)
        return super(FooScreen, self).add_widget(*args)


class FooApp(App):
    imp_text = StringProperty("Should change to text from id: magic_text")
    screen_magic = ObjectProperty()
    magic_layout = ObjectProperty()

    def build(self):
        self.title = 'Foo'
        self.root = root = Builder.load_string(kv_foo)

        # Trying stuff with References
        self.sm = self.root.ids.sm  # ScreenManager

        # Setting up screens for screen manager
        self.screens = {}
        self.available_screens = [kv_mainmenu, kv_magic]
        self.screen_names = ['MainMenu', 'Magic']
        self.go_screen(0)

    # Go to other screen
    def go_screen(self, idx):
        print("Change MainScreen to: {}".format(idx))
        self.index = idx
        # Go to not main menu
        if idx == 0:
            self.root.ids.sm.switch_to(self.load_screen(idx), direction='right')
        # Go to main menu
        else:
            self.root.ids.sm.switch_to(self.load_screen(idx), direction='left')

    # Load kv files
    def load_screen(self, index):
        if index in self.screens:
            return self.screens[index]
        screen = Builder.load_string(self.available_screens[index])
        self.screens[index] = screen
        # if index refers to 'Magic' (kv_magic), create reference
        if index == 1:
            Clock.schedule_once(lambda dt: self.create_reference())
        return screen

    # Trying to get id's
    def create_reference(self):
        print("\nrefs:")
        # Get screen from ScreenManager
        self.screen_magic = self.sm.get_screen(self.screen_names[1])
        # screen.boxlayout.magiclayout
        self.magic_layout = self.screen_magic.children[0].children[0]

    def change_text(self):
        # Get text from id: magic_text
        if self.magic_layout:
            self.imp_text = self.magic_layout.ids['magic_text'].text


kv_mainmenu = '''
FooScreen:
    id: mainm
    name: 'MainMenu'

    Button:
        text: 'Magic'
        on_release: app.go_screen(1)
'''

kv_magic = '''
<MagicLayout>
    id: magic_layout
    orientation: 'vertical'

    Label:
        id: magic_text
        text: root.m_text

FooScreen:
    id: magic_screen
    name: 'Magic'

    MagicLayout:
        id: testmagic
'''


class MagicLayout(BoxLayout):
    m_text = StringProperty("Reference between widgets test")


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

问题

如何设置正确的引用以使“更改上面的文本...”按钮可以检索 magic_text.text（“小部件之间的引用测试”）并将 self.imp_text 更改为 magic_text.text？

Answer 1

我找到了一种在不使用全局变量的情况下引用未在应用启动时加载的 Kivy 小部件的方法。感谢@inclement ScreenManager.get_screen()。

我必须添加以下代码：

class FooApp(App):
    screen_magic = ObjectProperty()
    magic_layout = ObjectProperty()

    ...

    # Trying to get id's
    def create_reference(self):
        print("\nrefs:")
        # Get screen from ScreenManager
        self.screen_magic = self.sm.get_screen(self.screen_names[1])
        # screen.boxlayout.magiclayout
        self.magic_layout = self.screen_magic.children[0].children[0]

    def change_text(self):
        # Get text from id: magic_text
        if self.magic_layout:
            self.imp_text = self.magic_layout.ids['magic_text'].text

self.screen_magic 分配了我需要的屏幕 (<FooScreen>)，self.magic_layout 分配了我需要的小部件 (<MagicLayout>)。然后我可以使用来自<MagicLayout> 的ID 来访问标签magic_text 的文本。

（完整代码见更新问题）