KivyMD 在更改屏幕上未使用 root.ids 创建 MDList 项目小部件并显示错误答案

【问题标题】：KivyMD on changing screen not creating MDList Items widget using root.ids and showing errorKivyMD 在更改屏幕上未使用 root.ids 创建 MDList 项目小部件并显示错误
【发布时间】：2021-06-09 10:32:48
【问题描述】：

我正在尝试使用 Kivymd 在 Python 中构建一个应用程序，并且我刚刚开始学习这个 kivymd 框架，所以我面临的问题是当我尝试将屏幕从 LoginScreen 更改为 HomeScreen 时，它会引发错误。我无法理解我的代码有什么问题。

我希望它将屏幕更改为 HomeScreen，然后在按下“加入聊天”按钮时显示列表。

代码如下：

main.py

from kivymd.app import MDApp
from kivy.lang import Builder
from kivy.uix.screenmanager import Screen,ScreenManager
from kivymd.uix.list import MDList, OneLineIconListItem,IconLeftWidget


class LoginScreen(Screen):
    pass

class HomeScreen(Screen):
    pass



class DemoApp(MDApp):
    def build(self):
        self.theme_cls.theme_style="Dark"
        
        self.sm=ScreenManager()
        self.sm.add_widget(LoginScreen(name="login"))
        self.sm.add_widget(HomeScreen(name="home"))

        screen=Builder.load_file("helper_file.kv")
        return screen
    
    def do_login(self):
        self.sm.current = "home"
        for i in range(20):
            st_name="student "
            list_item = OneLineIconListItem(text=f"student {str(i)}")
            list_item.add_widget(IconLeftWidget(icon= "alpha-a-box"))
            self.root.ids.users_lst.add_widget(list_item)

DemoApp().run()

helper_file.kv

ScreenManager:
    LoginScreen:
    HomeScreen:

<LoginScreen>:
    name: "login"
    Screen:
        MDLabel:
            text: "Demo App"
            halign: "center"
            pos_hint: {"center_x": .5, "center_y": .8}
            theme_text_color: "Primary"
        MDTextField:
            hint_text: "Enter username"
            helper_text: "to join the chat (test mode)"
            helper_text_mode: "on_focus"
            icon_right: "android"
            icon_right_color: app.theme_cls.primary_color
            pos_hint:{'center_x': 0.5, 'center_y': 0.5}
            size_hint_x:None
            width:311
        MDRoundFlatButton:
            text: "Join Chat"
            pos_hint: {"center_x": .5, "center_y": .4}
            on_release: app.do_login()
        MDLabel:
            text: "This is testing mode only"
            halign: "center"
            pos_hint: {"center_x": .5, "center_y": .2}
            theme_text_color:"Hint"

<HomeScreen>:
    name: "home"
    Screen:
        BoxLayout:
            orientation: "vertical"
            MDToolbar:
                title: "Demo Chat Application"
            ScrollView:
                MDList:
                    id: users_lst

运行此程序时，登录屏幕运行良好，但按下“加入聊天”按钮时会引发以下错误：

self.root.ids.users_lst.add_widget(list_item)
   File "kivy\properties.pyx", line 864, in kivy.properties.ObservableDict.__getattr__
 AttributeError: 'super' object has no attribute '__getattr__'

【问题讨论】：

请注意，在您的 build() 方法中，您构建了两次 GUI。一次是Buider.load_file()，一次是涉及self.sm 的行。应该删除涉及self.sm 的行。您的login() 方法中的self.sm.current = "home" 行也应该被删除（它没有做任何事情）。
或者你可以用self.root.current = "home"替换self.sm.current = "home"。

标签： python-3.x kivy kivy-language kivymd

【解决方案1】：

| 1 |

class HomeScreen(Screen):
    pass

<HomeScreen>:
    name: "home"
    Screen:
        BoxLayout:
            orientation: "vertical"
            MDToolbar:
                title: "Demo Chat Application"
            ScrollView:
                MDList:
                    id: users_lst

你有一个屏幕有一个屏幕，那不是你想要做的。

<HomeScreen>:
    name: "home"
    BoxLayout:
        orientation: "vertical"
        MDToolbar:
            title: "Demo Chat Application"
        ScrollView:
            MDList:
                id: users_lst

############################################## ######## ################################################# #####

| 2 |

父母无权访问内在儿童儿童的id。（不清楚我知道，所以我会给你很多打印以帮助你理解）。

    def do_login(self):
        self.root.current = "home"
        for i in range(20):
            st_name = "student "
            list_item = OneLineIconListItem(text=f"student {str(i)}")
            list_item.add_widget(IconLeftWidget(icon="alpha-a-box"))

            print("this is my App:", self)
            print("this is my ScreenManager:", self.sm)
            print("this is my global app visual widget (which is equal to ScreenManager here):", self.root)
            print("this is the ScreenManager's dictionnary containing the widgets referenced with their id:", self.root.ids)
            print("this is the current Screen:",self.root.current_screen)
            print("this is current Screen dictionnary containing the widgets referenced with their id:", self.root.current_screen.ids)
            print("this is the actual MDList", self.root.current_screen.ids["users_lst"])
            self.root.current_screen.ids["users_lst"].add_widget(list_item)

【讨论】：