raise FactoryException('Unknown class <%s>' % name) kivy.factory.FactoryException: Unknown class <OneLineListItem>

Question

I tried the MC Card Swipe example in the KivyMD documentation and found an error raise FactoryException('Unknown class <%s>' % name) kivy.factory.FactoryException: Unknown class ap

from kivy.lang import Builder
from kivy.properties import StringProperty

from kivymd.app import MDApp
from kivymd.uix.card import MDCardSwipe

KV = '''
<SwipeToDeleteItem>:
    size_hint_y: None
    height: content.height

    MDCardSwipeLayerBox:
        padding: "8dp"

        MDIconButton:
            icon: "trash-can"
            pos_hint: {"center_y": .5}
            on_release: app.remove_item(root)

    MDCardSwipeFrontBox:

        OneLineListItem:
            id: content
            text: root.text
            _no_ripple_effect: True


MDScreen:

    MDScrollView:

        MDList:
            id: md_list
            padding: 0
'''


class SwipeToDeleteItem(MDCardSwipe):
    text = StringProperty()


class Example(MDApp):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.theme_cls.theme_style = "Dark"
        self.theme_cls.primary_palette = "Orange"
        self.screen = Builder.load_string(KV)

    def build(self):
        return self.screen

    def remove_item(self, instance):
        self.screen.ids.md_list.remove_widget(instance)

    def on_start(self):
        super().on_start()
        for i in range(20):
            self.screen.ids.md_list.add_widget(
                SwipeToDeleteItem(text=f"One-line item {i}")
            )


Example().run()

I have tried various things, but still can't find a solution to this problem, Is there something wrong with my coding, please correct it