Android Bottom Navigation Bar with drop shadow

You can draw your own shadow just above the bottom bar using simple View and its background:

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

drawable/shadow.xml:

<shape xmlns:android="http://schemas.android.com/apk/res/android">    <gradient        android:startColor="#1F000000"        android:endColor="@android:color/transparent"        android:angle="90" /></shape>

Also, there are no compatibility issues if use this approach.

You can use elevation to add shadows to any view

<TextViewandroid:id="@+id/myview"...android:elevation="2dp"android:background="@drawable/myrect" />

Refer this for more information

For those using a CoordinatorLayout with the Bottom Navigation Bar (or BottomAppBar), you can use the following to attach a shadow above the bar:

<View    android:layout_width="match_parent"    android:layout_height="4dp"    android:background="@drawable/shadow"    app:layout_anchor="@+id/toolbar"    app:layout_anchorGravity="top"/>

Obviously, replace the @+id/toolbar with the id of the Bottom Navigation Bar