KivyMD：AttributeError：“NoneType”对象在添加 MDToolbar 时没有属性“theme_cls”

Question

我正在使用 Kivy 和 KivyMD，我正在尝试实现 MDToolbar。运行我的程序后，我收到此错误：AttributeError: 'NoneType' object has no attribute 'theme_cls'。我只包含了我的程序中的相关代码。在添加 MDToolbar 之前，一切都运行良好。我怎样才能让 MDToolbar 工作？请帮忙！

我的完整错误：

Parser: File "<inline>", line 22:
...
     20:<MDToolbar>
     21:    size_hint_y: None
>>   22:    height: root.theme_cls.standard_increment
     23:    padding: [root.theme_cls.horizontal_margins - dp(12), 0]
     24:    opposite_colors: True
...
AttributeError: 'NoneType' object has no attribute 'theme_cls'
  File "C:\Users\kelleym\AppData\Local\Continuum\anaconda3\lib\site-packages\kivy\lang\builder.py", line 696, in _apply_rule
    setattr(widget_set, key, value)
  File "kivy\weakproxy.pyx", line 35, in kivy.weakproxy.WeakProxy.__setattr__
  File "kivy\properties.pyx", line 497, in kivy.properties.Property.__set__
  File "kivy\properties.pyx", line 544, in kivy.properties.Property.set
  File "kivy\properties.pyx", line 599, in kivy.properties.Property.dispatch
  File "kivy\_event.pyx", line 1214, in kivy._event.EventObservers.dispatch
  File "kivy\_event.pyx", line 1120, in kivy._event.EventObservers._dispatch
  File "kivy\properties.pyx", line 1318, in kivy.properties.ReferenceListProperty.trigger_change
  File "kivy\properties.pyx", line 1333, in kivy.properties.ReferenceListProperty.trigger_change
  File "kivy\properties.pyx", line 599, in kivy.properties.Property.dispatch
  File "kivy\_event.pyx", line 1214, in kivy._event.EventObservers.dispatch
  File "kivy\_event.pyx", line 1120, in kivy._event.EventObservers._dispatch
  File "C:\Users\kelleym\AppData\Local\Continuum\anaconda3\lib\site-packages\kivymd\uix\behaviors\elevation.py", line 105, in _update_shadow
    self._shadow = App.get_running_app().theme_cls.quad_shadow
  File "C:\Users\kelleym\Desktop\Actual Inventory App\main.py", line 313, in <module>
    sm.add_widget(inventory(name='inventory'))

我的代码：

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivymd.theming import ThemeManager

Builder.load_string("""
<inventory>:
    NavigationLayout:
        id: "nav_layout"
        MDToolbar:
            title: "test"
        MDNavigationDrawer:
            drawer_logo: "test.png"
            id: "nav_drawer"
            NavigationDrawerSubheader:
                text: "[color=#black]Categories[/color]"
            NavigationDrawerIconButton:
                icon: 'printer'
                text: "Printers"
                on_release: root.manager.current = 'printers'
            NavigationDrawerIconButton:
                text: "PCs"
                icon: "laptop"
            NavigationDrawerIconButton:
                text: "Monitors"
                icon: "monitor"
            NavigationDrawerIconButton:
                text: "Tablets"
                icon: "tablet"
            NavigationDrawerIconButton:
                text: "Non-HP"
                icon: "close-circle-outline"
            NavigationDrawerIconButton:
                text: "Supplies"
                icon: "water"
            NavigationDrawerIconButton:
                text: "Misc."
                icon: "paperclip"
        Button:
            text: "test"
            on_release: app.nav_drawer.toggle()
""")


class inventory(BoxLayout, Screen):
    pass


sm = ScreenManager()
sm.add_widget(inventory(name='inventory'))


class TestApp(App):
    theme_cls = ThemeManager()

    def build(self):
        return sm


if __name__ == "__main__":
    TestApp().run()

Answer 1

此处的所有代码都适用于 Kivy 1.11.1 和 KivyMD 0.102.0。 KivyMD 处于 alpha 状态，未来可以更改 API。

1. 在 build 函数中创建所有小部件。您应该移动 ScreenManager 的创建：

    def build(self):
        sm = ScreenManager()
        sm.add_widget(inventory(name='inventory'))
        return sm

1. NavigationLayout 不能使用两个以上的小部件，其中一个是 MDNavigationDrawer，第二个是布局。创建BoxLayout并放入MDToolbar和Button：

    NavigationLayout:
        MDNavigationDrawer:
            # ...
            NavigationDrawerSubheader:
                # ...
        BoxLayout:
            orientation: "vertical"
            MDToolbar:
                title: "test"
            Button:
                text: "test"
                on_release: app.nav_drawer.toggle()

1. kv 代码中的Id 属性应不带"":

    NavigationLayout:
        id: nav_layout
        MDNavigationDrawer:
            id: nav_drawer

4. 要通过 id 调用小部件，您应该使用 app.root.ids.nav_drawer。

5. 要切换 NavigationDrawer，您应该调用 NavigationLayout：app.root.ids.nav_layout.toggle_nav_drawer()。

6. 通常 NavigationLayout 用作根小部件。将 ScreenManager 添加到 BoxLayout。

7. 您可以使用 kv 代码将屏幕添加到 ScreenManager：

        ScreenManager:
            id: screen_manager

            Inventory:
                name: "inventory"

8. 不要组合布局。不要写class Inventory(BoxLayout, Screen):。在屏幕内创建 BoxLayout：

<Inventory>:
    BoxLayout:
        orientation: "vertical"

---

最终代码为：

from kivy.app import App
from kivy.lang import Builder
from kivy.properties import ObjectProperty
from kivy.uix.screenmanager import Screen
from kivymd.theming import ThemeManager

root_kv = """
NavigationLayout:
    id: nav_layout

    MDNavigationDrawer:
        id: nav_drawer
        drawer_logo: "test.png"

        NavigationDrawerSubheader:
            text: "Categories"
        NavigationDrawerIconButton:
            text: "Printers"
            icon: "printer"
            on_release: app.screen_manager.current = "printers"
        NavigationDrawerIconButton:
            text: "PCs"
            icon: "laptop"
        NavigationDrawerIconButton:
            text: "Monitors"
            icon: "monitor"
        NavigationDrawerIconButton:
            text: "Tablets"
            icon: "tablet"
        NavigationDrawerIconButton:
            text: "Non-HP"
            icon: "close-circle-outline"
        NavigationDrawerIconButton:
            text: "Supplies"
            icon: "water"
        NavigationDrawerIconButton:
            text: "Misc."
            icon: "paperclip"

    BoxLayout:
        orientation: "vertical"

        ScreenManager:
            id: screen_manager

            Inventory:
                name: "inventory"


<Inventory>:
    BoxLayout:
        orientation: "vertical"

        MDToolbar:
            title: "test"

        Button:
            text: "test"
            on_release: app.root.toggle_nav_drawer()
"""


class Inventory(Screen):
    pass


class MainApp(App):
    theme_cls = ThemeManager()
    screen_manager = ObjectProperty()

    def build(self):
        self.root = Builder.load_string(root_kv)
        self.screen_manager = self.root.ids.screen_manager


if __name__ == "__main__":
    MainApp().run()

Answer 2

另一个有效的例子

from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
from kivy.properties import StringProperty, ListProperty

from kivymd.app import MDApp
from kivymd.theming import ThemableBehavior
from kivymd.uix.list import OneLineIconListItem, MDList

KV = '''
# 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: "KivyMD library"
        font_style: "Button"
        size_hint_y: None
        height: self.texture_size[1]

    MDLabel:
        text: "kivydevelopment@gmail.com"
        font_style: "Caption"
        size_hint_y: None
        height: self.texture_size[1]

    ScrollView:

        DrawerList:
            id: md_list



Screen:

    MDNavigationLayout:

        ScreenManager:

            Screen:

                BoxLayout:
                    orientation: 'vertical'

                    MDToolbar:
                        title: "Navigation Drawer"
                        elevation: 10
                        left_action_items: [['menu', lambda x: nav_drawer.set_state("open")]]

                    Widget:


        MDNavigationDrawer:
            id: nav_drawer
            
            ContentNavigationDrawer:
                id: content_drawer
                nav_drawer: nav_drawer
'''


class ContentNavigationDrawer(BoxLayout):
    pass


class ItemDrawer(OneLineIconListItem):
    icon = StringProperty()
    text_color = ListProperty((0, 0, 0, 1))


class DrawerList(ThemableBehavior, MDList):
    def set_color_item(self, instance_item):
        """Called when tap on a menu item."""

        # Set the color of the icon and text for the menu 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 TestNavigationDrawer(MDApp):
    def build(self):
        return Builder.load_string(KV)

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


TestNavigationDrawer().run()