如果不获取ValueError，如何访问类的根属性

Question

我是一名kivy/kivymd新手，正在学习如何按照kivymd网站( https://kivymd.readthedocs.io/en/0.104.0/components/navigation-drawer/)制作导航抽屉。我把我的代码放在最下面。

每当我运行代码时，它都会给出这个错误：

 kivy.lang.builder.BuilderException: Parser: File "<inline>", line 10:
 ...
       8:        icon: root.icon 
       9:        theme_text_color: "Custom"
 >>   10:        text_color: root.text_color
      11:        
      12:<ContentNavigationDrawer>:
 ...
 ValueError: None is not allowed for IconLeftWidget.text_color

我知道根是指尖括号中的父类，在本例中是ItemDrawer。所以我认为它应该做ItemDrawer.text_color。我对kivy和kivymd一无所知，我需要帮助来弄清楚如何解决这个问题！

这是我的代码。首先是包含我的字符串的python文件，Builder加载该文件：

proof_helper = """
<ItemDrawer>:
    theme_text_color: "Custom" 
    on_release: self.parent.set_color_item(self) 
    #invokes DrawerList set_color_item method

    IconLeftWidget:
        id: icon
        icon: root.icon 
        theme_text_color: "Custom"
        text_color: root.text_color
        
<ContentNavigationDrawer>:
    orientation: 'vertical'
    padding: '8dp'
    spacing: '8dp'
    
    ScrollView:
        DrawerList:
            id: md_list

Screen:
    MDNavigationLayout:
        ScreenManager:
            Screen:
                BoxLayout:
                    orientation: 'vertical'
                    MDToolbar:
                        title: "Navigation Drawer"
                        elevation: 8
                        left_action_items : [["menu", lambda x: nav_drawer.set_state()]]
                    
                    Widget:
                    
            Screen:
            
        MDNavigationDrawer:
            id: nav_drawer
            ContentNavigationDrawer:
                id: content_drawer
"""

这是我的main.py文件：

from kivymd.app import MDApp
from kivymd.theming import ThemableBehavior
from kivy.lang import Builder
from kivymd.uix.list import MDList, OneLineListItem, OneLineIconListItem
from kivy.core.window import Window
from proof_nav import proof_helper
from kivy.uix.boxlayout import BoxLayout
from kivy.properties import ObjectProperty, StringProperty

Window.size = (300, 500)


class ItemDrawer(OneLineIconListItem):
    icon = StringProperty()


class ContentNavigationDrawer(BoxLayout):
    pass


class DrawerList(ThemableBehavior, MDList):
    def set_color_item(self, instance_item):
        for item in self.children:
            if item.text_color == self.theme_cls.primary_color:
                item.text_color = self.theme_cls.text_color
                break
        instance_item.text_color = self.theme_cls.primary_color


class ProofApp(MDApp):
    def build(self):
        screen = Builder.load_string(proof_helper)
        return screen

    def on_start(self):
        icons_item = {
            "folder": "My files",
            "account-multiple": "Shared with me",
            "star": "Starred",
            "history": "Recent",
            "checkbox-marked": "Shared with me",
            "upload": "Upload",
        }

        for item in icons_item:
            self.root.ids.content_drawer.ids.md_list.add_widget(
                ItemDrawer(icon=item, text=icons_item[item])
            )


ProofApp().run()

Answer 1

OneLineIconListItem的默认text_color为None。如果您希望我们这样做，您必须将它的值设置为None以外的值。

你也可以这样做：

text_color: root.text_color if root.text_color else (0,0,0)