In the content_main.xml, we add the RecyclerView. Here is the code of this layout:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        tools:showIn="@layout/activity_main"
        tools:context=".ui.MainActivity">
    <android.support.v7.widget.RecyclerView
            android:id="@+id/recyclerview"
            android:background="@android:color/darker_gray"
            tools:listitem="@layout/recyclerview_item"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            android:layout_height="0dp" android:layout_width="0dp"/>
</android.support.constraint.ConstraintLayout>