donext/DoNExt/app/src/main/res/layout/activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".activities.MainActivity">

    <fragment
        android:id="@+id/fragment_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:name="com.wismna.geoffroy.donext.fragments.MainFragment"
        />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="end|bottom"
        android:layout_margin="@dimen/fab_margin"
        android:onClick="onNewTaskClick"
        android:src="@drawable/ic_add" />

</android.support.design.widget.CoordinatorLayout>