activity_main.xml

<android.support.v7.widget.RecyclerView
        android:id="@+id/mRecyclerView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="64dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintVertical_bias="0.09"
        android:scrollbars="vertical"
        app:layout_constraintTop_toTopOf="parent" />