<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_checked="true">
        <layer-list>
            <!--底层使用下划线的颜色填充-->
            <item>
                <shape>
                    <solid android:color="#3F617F"/>
                </shape>
            </item>
            <!--上面覆盖一层距离底层的底部3dp,填充白色。两层叠加一起就形成了一条下划线效果，原理自行脑补-->
            <item android:bottom="4dp">
                <shape>
                    <solid android:color="#ffffff"/>
                </shape>
            </item>
        </layer-list>
    </item>

    <!--<item android:state_pressed="true">
        <layer-list>
            <item>
                <shape>
                    <solid android:color="#797979"/>
                </shape>
            </item>
            <item android:bottom="3dp">
                <shape>
                    <solid android:color="#ffffff"/>
                </shape>
            </item>
        </layer-list>
    </item>-->

    <item
        android:drawable="@android:color/transparent">
    </item>

</selector>