KIVYMD 中堆叠类的属性名称无效

问：

from kivymd.app import MDApp
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.core.window import Window
from kivy.properties import ObjectProperty
from kivymd.uix.scrollview import MDScrollView
Window.clearcolor = (0, 0.6, 0.1, 1.0)
Window.size = (300, 500)

KV='''
#:import Snackbar kivymd.uix.snackbar.Snackbar
#signin screen with options as PATIENT, DOCTOR or GUEST
<HomeScreen>:
    name: "home_screen"
    MDScreen:
        FitImage:
            source: 'background_img.jpg'
        MDLabel:
            text:' Create an account! | SIGN-IN  '
            font_style:'H5'
            size_hint_y:None
            bold:True
            height:self.texture_size[1]
            halign:'center'
            pos_hint: {"center_x": .5, "center_y": .7}
        MDIconButton:
            text:'PATIENT'
            icon:'account'
            pos_hint: {"center_x": .4, "center_y": .4}
            width:100
            on_press:
                root.manager.current = 'p_login_screen'
                root.manager.transition.direction = "left"
                Snackbar(text="Fill in the above details to continue...").open()
        MDIconButton:
            text:'DOCTOR'
            icon:'doctor'
            pos_hint: {"center_x": .6, "center_y": .4}
            width:100
            on_press: 
                root.manager.current = 'd_login_screen'
                root.manager.transition.direction = "left"
                Snackbar(text="Fill in the above details to continue...").open()
        MDLabel:
            text:'or'
            font_style:'Subtitle2'
            size_hint_y:None
            bold:True
            height:self.texture_size[1]
            halign:'center'
            pos_hint: {"center_x": .5, "center_y": .3}
        MDTextButton:
            text:'Login as guest'
            font_style:'Caption'
            icon:'guest'
            pos_hint: {"center_x": .5, "center_y": .2}
            width:100
            on_press: root.manager.current = 'main.py'
            on_release: Snackbar(text="You have created account successfully!").open()
        MDLabel:
            text:'____________________________'
            font_style:'Subtitle2'
            size_hint_y:None
            bold:True
            height:self.texture_size[1]
            halign:'center'
            pos_hint: {"center_x": .5, "center_y": .156}
        MDTextButton:
            text:'Already a member?'
            font_style:'Caption'
            pos_hint: {"center_x": .5, "center_y": .1}
            width:100
            on_press: root.manager.current = 'main.py'
            on_release: Snackbar(text="You have created account successfully!").open()
#Patients login pages with various details
<P_login_Screen>
    name: "p_login_screen"
    MDScreen:
        MDLabel:
            text:'Create a patient account!'
            font_style:'H5'
            size_hint_y:None
            bold:True
            height:self.texture_size[1]
            halign:'center'
            pos_hint: {"center_x": .5, "center_y": .85}
            
        MDTextField:
            hint_text: "Enter name:"
            multiline:False
            required: True
            max_text_length: 25
            size_hint_x:None 
            line_color_focus: 0, 1, 0, 1
            mode: "round"
            icon_left: "account"
            icon_right_color: app.theme_cls.primary_color
            text_color_focus:1,0.5,1,1 
            pos_hint: {"center_x": .5, "center_y": .7}
            width:300
        MDTextField:
            hint_text: "Enter Gender:"
            multiline:False
            required: True
            line_color_focus: 0,1,0, 1
            mode: "round"
            size_hint_x:None 
            icon_left: "eye"
            icon_right_color: app.theme_cls.primary_color
            text_color_focus:1,0.5,1,1
            pos_hint: {"center_x": .5, "center_y": .6}
            width:300
        MDTextField:
            width:300
            hint_text: "Enter Age:"
            multiline:False
            max_text_length: 2
            required: True
            size_hint_x:None 
            line_color_focus: 0,1,0, 1
            mode: "round"
            icon_left: "help"
            text_color_focus:1,0.5,1,1
            pos_hint: {"center_x": .5, "center_y": .5}
        MDTextField:
            hint_text: "Enter Phone number:"
            multiline:False
            max_text_length: 10 
            required: True
            size_hint_x:None 
            line_color_focus: 0,1,0, 1
            mode: "round"
            icon_left: "phone"
            icon_right_color: app.theme_cls.primary_color
            text_color_focus:1,0.5,1,1
            pos_hint: {"center_x": .5, "center_y": .4}
            width:300
        MDTextField:
            hint_text: "Enter E-Mail:"
            multiline:False
            helper_text: "Enter valid email"
            required: True
            line_color_focus: 0,1,0, 1
            mode: "round"
            size_hint_x:None 
            icon_left: "gmail"
            icon_right_color: app.theme_cls.primary_color
            validator: "email"
            text_color_focus:1,0.5,1,1
            pos_hint: {"center_x": .5, "center_y": .3}
            width:300
        
        MDRectangleFlatButton:
            text:'Sumbit!'
            pos_hint: {"center_x": .5, "center_y": .2}
            width:300
            on_press: root.manager.current = 'main.py'
            on_release: Snackbar(text="You have created account successfully!").open()
        MDIconButton:
            icon:'chevron-left'
            pos_hint: {"center_x": .125, "center_y": .075}
            width:100
            on_press: 
                root.manager.current = 'home_screen'
                root.manager.transition.direction = "right"
    
<D_login_Screen>
    name: "d_login_screen"
    MDScreen:
        MDLabel:
            text:'Create a doctor account!'
            font_style:'H5'
            size_hint_y:None
            bold:True
            height:self.texture_size[1]
            halign:'center'
            pos_hint: {"center_x": .5, "center_y": .85}
            
        MDTextField:
            hint_text: "Enter name:"
            multiline:False
            required: True
            max_text_length: 25
            size_hint_x:None 
            line_color_focus: 0, 1, 0, 1
            mode: "round"
            icon_left: "account"
            icon_right_color: app.theme_cls.primary_color
            text_color_focus:1,0.5,1,1 
            pos_hint: {"center_x": .5, "center_y": .7}
            width:300
        MDTextField:
            hint_text: "Enter Gender:"
            multiline:False
            required: True
            line_color_focus: 0,1,0, 1
            mode: "round"
            size_hint_x:None 
            icon_left: "eye"
            icon_right_color: app.theme_cls.primary_color
            text_color_focus:1,0.5,1,1
            pos_hint: {"center_x": .5, "center_y": .6}
            width:300
        MDTextField:
            width:300
            hint_text: "Enter Age:"
            multiline:False
            max_text_length: 2
            required: True
            size_hint_x:None 
            line_color_focus: 0,1,0, 1
            mode: "round"
            icon_left: "help"
            text_color_focus:1,0.5,1,1
            pos_hint: {"center_x": .5, "center_y": .5}
        MDTextField:
            hint_text: "Enter Phone number:"
            multiline:False
            max_text_length: 10 
            required: True
            size_hint_x:None 
            line_color_focus: 0,1,0, 1
            mode: "round"
            icon_left: "phone"
            icon_right_color: app.theme_cls.primary_color
            text_color_focus:1,0.5,1,1
            pos_hint: {"center_x": .5, "center_y": .4}
            width:300
        MDTextField:
            hint_text: "Enter E-Mail:"
            multiline:False
            helper_text: "Enter valid email"
            required: True
            line_color_focus: 0,1,0, 1
            mode: "round"
            size_hint_x:None 
            icon_left: "gmail"
            icon_right_color: app.theme_cls.primary_color
            validator: "email"
            text_color_focus:1,0.5,1,1
            pos_hint: {"center_x": .5, "center_y": .3}
            width:300
        MDRectangleFlatButton:
            text:'Sumbit!'
            pos_hint: {"center_x": .5, "center_y": .2}
            width:300
            on_press: root.manager.current = 'main.py'
            on_release: Snackbar(text="You have created account successfully!").open()
        MDIconButton:
            icon:'chevron-left'
            pos_hint: {"center_x": .125, "center_y": .075}
            width:100
            on_press: 
                root.manager.current = 'home_screen'
                root.manager.transition.direction = "right"
<MAINScreen>
    name: "main.py"
    <ContentNavigationDrawer>:
    
        MDList:
            spacing:'8dp'
            padding:'8dp'

            MDLabel:
                text:'Health CheckUp App'
                font_style:'Subtitle1'
                size_hint_y:None
                bold:True
                height:self.texture_size[1]

            MDLabel:
                text:'Created by VIGNESH.C'
                font_style:'Caption'
                size_hint_y:None
                height:self.texture_size[1]

            OneLineAvatarIconListItem:
                text: "Home"
                on_press:
                    root.nav_drawer.set_state("close")
                    root.screen_manager.current = "scr 1"
                IconLeftWidget:
                    icon: "home"
                    on_press:
                        root.screen_manager.current = "scr 1"

            OneLineAvatarIconListItem:
                text: "Settings"
                on_press:
                    root.nav_drawer.set_state("close")
                    root.screen_manager.current = "scr 2"
                IconLeftWidget:
                    icon: "widgets"
                    on_press:
                        root.screen_manager.current = "scr 2"


    MDScreen:

        MDTopAppBar:
            pos_hint: {"top": 1}
            elevation: 4
            title: "Health CheckUp App"
            left_action_items: [["menu", lambda x: nav_drawer.set_state("open")]]
            right_action_items: [["account-circle", lambda x: nav_drawer.set_state("open")]]

        MDNavigationLayout:

            MDScreenManager:
                id: screen_manager

                MDScreen:
                    name: "scr 1"
                    MDLabel:
                        text:'Dashboards'
                        font_name:"Comic"
                        color:1,.5,1,1

                        font_size:30
                        pos_hint:{'center_x':.2,'center_y':.7}
                        texture_size: self.size
                        text_size: self.size
                    MDFloatingActionButtonSpeedDial:
                        icon:'phone'
                        data:app.data
                        root_button_anim:True
                        hint_animation:True
                        bg_color_root_button:"red"
                        bg_color_stack_button:"green"
                        bg_hint_color:'grey'
                        color_icon_stack_button:'white'
                        label_text_color: "white"

                MDScreen:
                    name: "scr 2"

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

            MDNavigationDrawer:
                id: nav_drawer
                radius: (0, 16, 16, 0)

                ContentNavigationDrawer:
                    screen_manager: screen_manager
                    nav_drawer: nav_drawer

<RootWidget>:
    HomeScreen:
        name: "home_screen"
    D_login_Screen:
        name:'d_login_screen'
    P_login_Screen:
        name: "p_login_screen"
    MAINScreen:
        name:'main.py'
    ContentNavigationDrawer:
        name:'cont'
            
    
'''
class HomeScreen(Screen):
    pass
class P_login_Screen(Screen):
    pass
class D_login_Screen(Screen):
    pass
class MAINScreen(Screen):
    pass
class ContentNavigationDrawer(MDScrollView):
    screen_manager = ObjectProperty()
    nav_drawer = ObjectProperty()

class RootWidget(ScreenManager):
    pass



Builder.load_string(KV)
class MainApp(MDApp):
    data= {
                'Ambulance':'ambulance',
                'Doctor':'doctor',
                "Home":'home',
            }
    def build(self):
        self.title = "Health CheckUp App"
        return RootWidget()
if __name__ == "__main__":
    MainApp().run()

我收到此错误： >> 249： ： 250：251：MDList：
... 属性名称无效

如何更正我的代码????

无错误页面，带有干净的动画和小部件

需要的是，当我单击“以访客身份登录”时，我应该得到一个包含所有小部件的页面，当我单击左上角的菜单按钮时，我应该得到一个带有屏幕过渡的列表。