activity_montar_barreta.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    android:background="@color/grey"
    tools:context=".MainActivity">

    <android.support.v7.widget.Toolbar
        android:id="@+id/tb_mont"
        android:elevation="4dp"
        android:layout_height="?attr/actionBarSize"
        android:layout_width="match_parent"
        android:minHeight="?attr/actionBarSize"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:background="?attr/colorPrimary"
        app:theme="@style/AppTheme.AppBarOverlay"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Dark" />

  <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_montar_barreta"
        android:scrollbars="vertical"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"

      android:layout_below="@+id/tb_mont"
      android:layout_alignParentLeft="true"
      android:layout_alignParentStart="true" />

    </RelativeLayout>