Remove android.widget.Toolbar shadow

Use attribute app:elevation="0dp" to your Toolbar or AppBarLayout to remove the shadow.

#. If you are using Toolbar only, then add attribute app:elevation="0dp" to Toolbar.

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:popupTheme="@style/AppTheme.PopupOverlay"
        app:elevation="0dp"/>

#. If you are using AppBarLayout as a container of Toolbar, then add attribute app:elevation="0dp" to AppBarLayout.

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay"
        app:elevation="0dp">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

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

OUTPUT:

UPDATE:

If you want to remove it programmatically then you can use below code:

getSupportActionBar().setElevation(0);

Hope this will help~

Instead of android:elevation try app:elevation:

<android.support.design.widget.AppBarLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/appbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"       
    app:elevation="0dp">
</android.support.design.widget.AppBarLayout>

Use app:elevation="0dp" instead of android:elevation on your toolbar. If it is not work, put your toolbar inside of a AppBarLayout and set app:elevation="0dp":

<android.support.design.widget.AppBarLayout
            android:id="@+id/appBarLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:elevation="0dp">
            ...
</android.support.design.widget.AppBarLayout>