Collapsing toolbar when scrolling list using ViewPager with TabLayout

CollapsingToolbarTabLayout.kt

class ListSelectorActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_list_selector)
        setSupportActionBar(toolbar)

        createViewPageAdapter()

        fab.setOnClickListener {
            viewPager.setCurrentItem(1, true)
        }
    }

    private fun createViewPageAdapter() {
        viewPager.adapter = ListSelectorAdpter(supportFragmentManager, this)
        tabs.setupWithViewPager(viewPager)
    }

}

CollapsingToolbarTabLayout.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".activities.ListSelectorActivity">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <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"
            app:layout_scrollFlags="scroll|enterAlways" />

        <android.support.design.widget.TabLayout
            android:id="@+id/tabs"
            app:tabMode="fixed"
            android:layout_below="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:elevation="0dp"
            app:tabTextColor="#d3d3d3"
            app:tabSelectedTextColor="#ffffff"
            app:tabIndicatorColor="#ff00ff"
            android:minHeight="?attr/actionBarSize"/>

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

    <android.support.v4.view.ViewPager
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        android:src="@drawable/ic_chat" />

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

FragmentViewPager.xml

<!-- FILE USING IN FRAGMENT -->
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_height="match_parent"
    android:paddingStart="@dimen/layoutPaddingStart"
    android:paddingEnd="@dimen/layoutPaddingEnd"
    android:paddingBottom="@dimen/layoutPaddingBottom">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        app:layoutManager="android.support.v7.widget.LinearLayoutManager"/>


</android.support.constraint.ConstraintLayout>