app/src/main/res/layout/activity_main.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"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/nfd_button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="toggleNfdState"
        android:enabled="false"
        android:text="@string/checking_on_nfd" />

    <Button
        android:id="@+id/launch_logger"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/nfd_button"
        android:onClick="launchLogActivity"
        android:text="@string/launch_logger" />

</RelativeLayout>