问带有导航抽屉的kivy屏幕中未显示标签

EN

#:import FadeTransition kivy.uix.screenmanager.FadeTransition
# Menu item in the DrawerList list.
<ItemDrawer>:
    theme_text_color: "Custom"
    on_release: self.parent.set_color_item(self)

    IconLeftWidget:
        id: icon
        icon: root.icon
        theme_text_color: "Custom"
        text_color: root.text_color


<ContentNavigationDrawer>:
    orientation: "vertical"
    padding: "8dp"
    spacing: "8dp"

    AnchorLayout:
        anchor_x: "left"
        size_hint_y: None
        height: avatar.height

        Image:
            id: avatar
            size_hint: None, None
            size: "56dp", "56dp"
            source: "data/logo/kivy-icon-256.png"

    MDLabel:
        text: "Voice Cloning Tool"
        font_style: "Button"
        size_hint_y: None
        height: self.texture_size[1]

    MDLabel:
        text: "MENU"
        font_style: "Caption"
        size_hint_y: None
        height: self.texture_size[1]

    ScrollView:

        DrawerList:
            OneLineListItem:
                text:'Home'
                on_release:app.root.current='home_screen'

            OneLineListItem:
                text:'Record Voice'
                on_release:app.root.current='rec_screen'
            OneLineListItem:

                text:'Help'
            OneLineListItem:

                text:'About'
            OneLineListItem:
                text:'Contact Us'
ScreenManagement:
    transition:FadeTransition()
    HomeScreen:
    RecordScreen:
    AboutScreen:
    ContactUSScreen:

<HomeScreen>:
    name:'home_screen'

    NavigationLayout:

        ScreenManager:

            Screen:
                SliderWin

                BoxLayout:
                    orientation: 'vertical'

                    MDToolbar:
                        title: "Explore Voice cloning Tool"
                        elevation: 10
                        left_action_items: [['menu', lambda x: nav_drawer.toggle_nav_drawer()]]

                    Widget:


        MDNavigationDrawer:
            id: nav_drawer

            ContentNavigationDrawer:
                id: content_drawer

<RecordScreen>:
    name:'rec_screen'

    NavigationLayout:

        ScreenManager:

            Screen:



                BoxLayout:

                    orientation: 'vertical'

                    MDToolbar:
                        title: "Explore Voice cloning Tool"
                        elevation: 10
                        left_action_items: [['menu', lambda x: nav_drawer.toggle_nav_drawer()]]
                    Label:

                        text:'Hello World'
                        size_hint:0.5,0.1
                        pos_hint:{'x':0.5,'y':0.5}
                        color:1,0,1,1

                    Button:
                        text:'Hello World'
                        size_hint:0.5,0.1
                        pos_hint:{'x':0.5,'y':0.5}



        MDNavigationDrawer:
            id: nav_drawer

            ContentNavigationDrawer:
                id: content_drawer