view添加底部阴影

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="rectangle">
            <solid android:color="#17000000" />
        </shape>
    </item>

    <item
        android:bottom="4dp"
        android:left="0dp"
        android:right="0dp"
        android:top="0dp">
        <shape android:shape="rectangle">
            <solid android:color="#FFFFFFFF" />
        </shape>
    </item>

</layer-list>