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我是使用 kivymd 并尝试使用 KivyMD 在 NavigationDrawer 中的屏幕之间切换的初学者，我正在阅读一些文档并最终得到了这段代码，但它不适用于我：

from kivy.lang import Builder
from kivy.core.window import Window
from kivy.uix.boxlayout import BoxLayout
from kivy.properties import ObjectProperty
from kivymd.theming import ThemableBehavior
from kivymd.uix.list import MDList
from kivymd.app import MDApp



Window.size = (300, 500)
navigation_helper = """
Screen:
    MDToolbar:
        id: toolbar
        pos_hint: {"top": 1}
        elevation: 10
        title: "MDNavigationDrawer"
        left_action_items: [["menu", lambda x: nav_drawer.set_state("open")]]
        
    NavigationLayout:
        x: toolbar.height

        ScreenManager:
            id: screen_manager

            Screen:
                name: "scr 1"

                MDLabel:
                    text: "Go to Hell"
                    halign: "center"

            Screen:
                name: "scr 2"

                MDLabel:
                    text: "Hell"
                    halign: "center"

        MDNavigationDrawer:
            id: nav_drawer

            ContentNavigationDrawer:
                screen_manager: screen_manager
                nav_drawer: nav_drawer
           
                ScrollView:
                    MDList:

                        OneLineListItem:
                            text: "Screen 1"
                            on_press:
                                root.nav_drawer.set_state("close")
                                root.screen_manager.current = "scr 1"
            
                        OneLineListItem:
                            text: "Screen 2"
                            on_press:
                                root.nav_drawer.set_state("close")
                                root.screen_manager.current = "scr 2"


"""



class DemoApp(MDApp):
    class ContentNavigationDrawer(BoxLayout):
        screen_manager = ObjectProperty()
        nav_drawer = ObjectProperty()

    class DrawerList(ThemableBehavior, MDList):
        pass

    def build(self):
        screen = Builder.load_string(navigation_helper)
        return screen

    def on_start(self):
        pass


DemoApp().run()

但它给了我这个错误“AttributeError：'Screen'对象没有属性'nav_drawer'”，我不确定我做错了什么。

4

1 回答 1

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id当您在定义 的同一规则中使用 an 引用对象时id，您不需要在它前面加上root：

                    OneLineListItem:
                        text: "Screen 1"
                        on_press:
                            nav_drawer.set_state("close")
                            screen_manager.current = "scr 1"

                    OneLineListItem:
                        text: "Screen 2"
                        on_press:
                            nav_drawer.set_state("close")
                            screen_manager.current = "scr 2"
于 2020-07-21T17:18:14.213 回答