<RelativeLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_height="match_parent"
        android:layout_width="match_parent">
    <ScrollView
                android:layout_width="match_parent"
                android:layout_height="match_parent">
        <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="vertical">

A LOT OF CONTENT


        </LinearLayout>
    </ScrollView>

    <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:id="@+id/add"
            android:text="@string/add"
            android:paddingTop="23dp"/>
</RelativeLayout>

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent">
    <ScrollView
        android:layout_width="match_parent"
        android:layout_above="@+id/add"
        android:layout_height="match_parent">
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">

            A LOT OF CONTENT


        </LinearLayout>
    </ScrollView>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:id="@+id/add"
        android:text="@string/add"
        android:paddingTop="23dp"/>
</RelativeLayout>