Material TabLayout elevation not working

Question

For some reason the elevation attribute does not seem to be working on the new TabLayout in the material design support library. Any ideas? XML:

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

<android.support.design.widget.TabLayout
    android:id="@+id/tab_layout"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:elevation="6dp" />

<android.support.v4.view.ViewPager
    android:id="@+id/view_pager"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1" />
</LinearLayout>

hooked up like this in a parent fragment:

ViewPager viewPager = (ViewPager) view.findViewById(R.id.view_pager);
TabLayout tabLayout = (TabLayout) view.findViewById(R.id.tab_layout);
AppPagerAdapter appPagerAdapter = new AppPagerAdapter(getChildFragmentManager());
viewPager.setAdapter(appPagerAdapter);
tabLayout.setupWithViewPager(viewPager);

image:

The activity has a toolbar but this is outside of the fragment and should not affect the tablayout's ability to have a shadow:

relevant activity xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.bluckapps.appinfomanager.ui.MainActivity">

<android.support.v7.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="?attr/colorPrimary"
    android:elevation="6dp"
    android:minHeight="?attr/actionBarSize"
    tools:ignore="UnusedAttribute" />

<FrameLayout
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1" />

</LinearLayout>

Answer 1

To make the shadow show, you have to set a background on your TabLayout. It can be the same color as your window background (as long as it's a solid color with no alpha).

<android.support.design.widget.TabLayout
    android:id="@+id/tab_layout"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:elevation="6dp"
    android:background="@color/white" />