KivyMD自定义类跨应用使用问题：导入后仅显示空白MDCard

出现空白MDCard的核心原因有三个：

1. easymd.py中的KV样式规则未被加载，自定义类的布局逻辑完全没生效
2. SegmentedControl继承自MDCard，而MDCard不是布局容器，无法直接添加子控件
3. 主程序中多余的Segment多重继承类属于无效代码，无任何作用

1. 修改easymd.py文件 #

加载KV样式，并让SegmentedControl支持容纳子控件：

from kivymd.uix.card import MDCard
from kivymd.uix.boxlayout import MDBoxLayout
from kivy.properties import ObjectProperty, BooleanProperty, StringProperty, ColorProperty
from kivy.lang import Builder

kv = '''
<SegmentedControl>:
    id: segment_panel
    size_hint_y: None
    height: self.minimum_height
    md_bg_color: 'red' if not self.segment_color else self.segment_color
    # 内部嵌套布局容器，用于存放子项
    MDBoxLayout:
        id: container
        orientation: 'horizontal'
        size_hint: 1, 1
        spacing: 0

<SegmentedControlItem>:
    id: s1
    text: ''
    color: 'black'
    size_hint_y: None
    height: self.minimum_height
    elevation: 0
    md_bg_color: 'red' if not s1.active else '#4CAF50'
    padding: 20

    MDLabel:
        id: l1
        size_hint_y: None
        text: s1.text
        halign: 'center'
        color: s1.color
        pos_hint: {"center_y": .5}
        height: self.texture_size[1]
'''

# 加载自定义KV样式
Builder.load_string(kv)

class SegmentedControl(MDCard):
    segment_color = ColorProperty(None)
    container = ObjectProperty(None)

    # 重写add_widget，将子项添加到内部布局容器
    def add_widget(self, widget, index=0, canvas=None):
        if isinstance(widget, SegmentedControlItem):
            self.container.add_widget(widget)
        else:
            super().add_widget(widget, index, canvas)

class SegmentedControlItem(MDCard):
    segment_color = ColorProperty(None)
    active = BooleanProperty(True)
    text = StringProperty('')
    color = ColorProperty('black')

2. 修改主程序代码 #

删除无效的多重继承类，简化逻辑：

from kivymd.app import MDApp
from kivy.lang import Builder
from easymd import SegmentedControl, SegmentedControlItem

kv = '''
MDBoxLayout:
    orientation: 'vertical'
    md_bg_color: 'pink'
    padding: 20
    SegmentedControl:
        SegmentedControlItem:
            text: 'Hello'
        SegmentedControlItem:
            text: 'World'
            active: False
'''

class SegmentSwapApp(MDApp):
    def build(self):
        return Builder.load_string(kv)

if __name__ == '__main__':
    SegmentSwapApp().run()

• 加载KV样式：通过Builder.load_string(kv)让自定义类的布局规则生效
• 支持子控件嵌套：在SegmentedControl内部添加MDBoxLayout容器，并重写add_widget方法，确保子项被正确添加到容器中
• 完善属性绑定：给SegmentedControlItem显式定义text、color属性，保证KV中的绑定逻辑正常工作
• 状态可视化：给SegmentedControlItem添加active状态对应的背景色变化，方便区分选中/未选中状态

内容的提问来源于stack exchange，提问作者Mr Stranger