activity_bluetooth.xml

<!-- activity_bluetooth.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"
    tools:context=".BluetoothActivity">

    <Button
        android:id="@+id/btnScan"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Scan"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="16dp"/>

    <ListView
        android:id="@+id/listView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@id/btnScan"
        android:layout_marginTop="16dp" />

</RelativeLayout>