app/src/main/res/layout/content_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="io.v.todos.MainActivity"
    tools:showIn="@layout/activity_main">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <android.support.v7.widget.RecyclerView android:id="@+id/recycler"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            app:layoutManager="LinearLayoutManager" />
        <TextView android:id="@+id/empty"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#FF0000"
            android:text="No data"/>
    </LinearLayout>
    <android.support.design.widget.FloatingActionButton
        android:layout_height="wrap_content"
        android:layout_width="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        app:fabSize="normal"
        android:src="@android:drawable/ic_input_add"
        android:layout_margin="@dimen/fab_margin"
        android:clickable="true"
        android:onClick="addCallback"/>
</RelativeLayout>