为switchcompat的拇指添加渐变

Question

我想在switchcompat的拇指上添加一个颜色渐变。

<androidx.appcompat.widget.SwitchCompat
            android:layout_width="50dp"
            android:checked="true"
            android:layout_height="50dp"
            android:thumb="@drawable/switch_thumb"      
 />

drawable switch_thumb.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list
        xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="oval">
            <gradient
                    android:startColor="@color/thumb_start_gradient"
                    android:endColor="@color/thumb_end_gradient"/>

        </shape>
    </item>
    <item
            android:bottom="2dp"
            android:left="1dp"
            android:right="1dp"
            android:top="1dp">
        <shape android:shape="oval">
            <gradient
                    android:startColor="@color/thumb_start_gradient"
                    android:endColor="@color/thumb_end_gradient"/>
        </shape>
    </item>
    <item>

        <shape android:shape="oval">
            <solid android:color="#0f0"/>
        </shape>

    </item>
</layer-list>

但是它甚至没有画出开关。