android manual shadow

drawable-shadow.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <gradient
        android:angle="90"
        android:endColor="#44000000"
        android:startColor="@android:color/transparent" />
</shape>

layout-shadow.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <View
        android:layout_width="match_parent"
        android:layout_height="4dp"
        android:background="@drawable/shadow" />
</FrameLayout>