kivymd中的断言错误

Question

我试图在屏幕管理器中添加屏幕，但在屏幕管理器中分配导航抽屉时给出了断言错误

这就是我面临的错误： 自我。应用规则( 文件“/home/hp/.local/lib/python3.8/site packages/kivy/lang/builder.py”，第559行，在应用规则中 断言（规则不在self.rulectx中） 断言者

这是我的代码：

from kivymd.app import MDApp
from kivy.lang.builder import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.properties import ObjectProperty
from kivy.uix.boxlayout import BoxLayout
screen_helper = """
ScreenManager:
    MenuScreen:
    ProfileScreen:
    ContentNavigationDrawer:
<MenuScreen>:
    name: 'menu'
    MDRectangleFlatButton:
        text: 'Profile'
        pos_hint: {'center_x':0.5,'center_y':0.6}
        on_press: root.manager.current = 'profile'
    MDRectangleFlatButton:
        text: 'Upload'
        pos_hint: {'center_x':0.5,'center_y':0.5}
        on_press: root.manager.current = 'upload'
    
<ProfileScreen>:
    name: 'profile'
    MDLabel:
        text: 'Profile'
        halign: 'center'
    MDRectangleFlatButton:
        text: 'Back'
        pos_hint: {'center_x':0.5,'center_y':0.1}
        on_press: root.manager.current = 'menu'
<ContentNavigationDrawer>:
    name : 'upload'
    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"


    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: "Screen 1"
                        halign: "center"

                Screen:
                    name: "scr 2"

                    MDLabel:
                        text: "Screen 2"
                        halign: "center"

            MDNavigationDrawer:
                id: nav_drawer

                ContentNavigationDrawer:
                    screen_manager: screen_manager
                    nav_drawer: nav_drawer
"""


class MenuScreen(Screen):
    pass


class ProfileScreen(Screen):
    pass


class ContentNavigationDrawer(Screen):
    screen_manager = ObjectProperty()
    nav_drawer = ObjectProperty()


# Create the screen manager
sm = ScreenManager()
sm.add_widget(MenuScreen(name='menu'))
sm.add_widget(ProfileScreen(name='profile'))
sm.add_widget(ContentNavigationDrawer(name='upload'))


class DemoApp(MDApp):

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


DemoApp().run()

Answer 1

我认为问题在于你在{}中的规则：

<ContentNavigationDrawer>:

包括：

            ContentNavigationDrawer:
                screen_manager: screen_manager
                nav_drawer: nav_drawer

这个规则组合告诉kivy，每当它创建一个ContentNavigationDrawer时，它应该创建另一个ContentNavigationDrawer作为第一个的子级。然后它会尝试再次应用原始<ContentNavigationDrawer>:，创建第三个ContentNavigationDrawer，再次应用规则创建第四个，依此类推。这将创建一个无限循环。Kivy使用assertion来避免这种循环。因此，您不能使用创建这样一个循环的规则