Set custom shadow to AppBarLayout or Toolbar

Question

I want to set custom shadow to Toolbar. Currently is shown default shadow, but it not appropriate for me. So how can I set a custom shadow?

Activity layout:

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbarMain"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize" />

</android.support.design.widget.AppBarLayout>

Answer 1

Finally I found it out. But this approach do not give the same shadow as BottomNavigationView has. This is a minor issue, but maybe you have suggestions?

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:elevation="0dp">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbarMain"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:minHeight="?attr/actionBarSize" />

</android.support.design.widget.AppBarLayout>

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1"
    android:background="@color/PageBackground">

    <FrameLayout
        android:id="@+id/frameContainer"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1" />

    <View
        android:layout_width="match_parent"
        android:layout_height="2dp"
        android:background="@drawable/app_bar_shadow" />

</RelativeLayout>

app_bar_shadow.xml:

<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <gradient
        android:angle="270"
        android:startColor="#15000000"
        android:endColor="@android:color/transparent"
        android:type="linear" />
</shape>