Problem with position of floating action button about expandable-recycler-view HOT 4 CLOSED

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:background="#000000">

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="right|bottom"
        android:layout_marginBottom="16dp"
        android:layout_marginRight="16dp"
        android:src="@drawable/ic_add_white_24dp" />

    <android.support.v7.widget.RecyclerView
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/weatherList"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</RelativeLayout>