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/start_nfd_button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="startNFD"
        android:text="Start NFD" />

    <Button
        android:id="@+id/stop_nfd_button"
        android:layout_below="@id/start_nfd_button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="stopNFD"
        android:text="Stop NFD" />

    <Button
        android:id="@+id/start_nfd_explicit_button"
        android:layout_below="@id/stop_nfd_button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="startNFDexplicit"
        android:text="Start NFD explicit!" />

    <Button
        android:id="@+id/start_nfd_jni"
        android:layout_below="@id/start_nfd_explicit_button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="startNfd"
        android:text="Start NFD through JNI" />

    <Button
        android:id="@+id/stop_nfd_jni"
        android:layout_below="@id/start_nfd_jni"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="stopNfd"
        android:text="Stop NFD through JNI" />
</RelativeLayout>