how to implement BlueTooth class; what should it extend; compile errors at startActivityForResult and registerReceiver

I have created one tab layout in main activity. It sets 3 tabs. In settings tab(which is extending ListFragment) I am handling click event on list. When 1st element is clicked, it creates BlueTooth object bt. Bluetooth extends activity.Inside that I am handling bluetooth functions.But bluetooth functions do not seem to be called. Pasting the code settings tab

   //Our class extending fragment
    public class settings extends ListFragment /*Fragment*/implements OnItemClickListener {
        String[] title = {
                "Register",
                "Set Password",
                "Edit Password",
                "Delete Password",
                "Add location to turn-off place list",
                "Disable turn-off Places",
                "Enable turn-off Places",
                "Edit Distance",
                "Factory Reset"
        };

        List<String> mStrings = new ArrayList<String>();
        List<String> mDevices = new ArrayList<String>();

        String[] strings = new String[mStrings.size()];
        //Overriden method onCreateView
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

            //Returning the layout file after inflating
            //Change R.layout.tab1 in you classes
            return inflater.inflate(R.layout.fragment_pager_list, container, false);
        }
        @Override
        public void onActivityCreated(Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);
            for(int i=0;i<title.length;i++) {
                mStrings.add(title[i]);

            }
            strings = mStrings.toArray(strings);
            setListAdapter(new ArrayAdapter<String>(getActivity(),
                    android.R.layout.simple_list_item_1,
                    mStrings));
            getListView().setOnItemClickListener(this);
        }



        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position,long id) {
            //Toast.makeText(getActivity(), "Item: " + position, Toast.LENGTH_SHORT).show();
            switch(position)
            {
                case 0:

                    Intent intent = new              Intent(getActivity().getApplicationContext(), BlueTooth.class);
startActivity(Intent intent);
                    mDevices.add("Dev1");
                    setListAdapter(new ArrayAdapter<String>(getActivity(),
                            android.R.layout.simple_list_item_1,
                            mDevices));
                    break;
                .....



            }
        }
    }

Bluetooth class:

public class BlueTooth extends Activity {

    private BluetoothAdapter mBTA;
    private SignBroadcastReceiver mReceiver;
    boolean discoverFlag = false;
    /** Called when the activity is first created. */

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.main);

        //register local BT adapter
        mBTA = BluetoothAdapter.getDefaultAdapter();
        //check to see if there is BT on the Android device at all
        if (mBTA == null) {
            int duration = Toast.LENGTH_SHORT;
            Toast.makeText(this, "No Bluetooth on this handset", duration).show();
        }
        //let's make the user enable BT if it isn't already
        /*if (!mBTA.isEnabled()) {
            Intent enableBT = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBT, 0xDEADBEEF);
        }*/
        Intent discoverableIntent =
                new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
        discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300);
        startActivityForResult(discoverableIntent,0);

        if(discoverFlag) {
            //cancel any prior BT device discovery
            if (mBTA.isDiscovering()) {
                mBTA.cancelDiscovery();
            }
            //re-start discovery
            mBTA.startDiscovery();

            //let's make a broadcast receiver to register our things
            mReceiver = new SignBroadcastReceiver();
            IntentFilter ifilter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
            this.registerReceiver(mReceiver, ifilter);
        }
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent intent) {
        System.out.println(resultCode);
        if (resultCode ==  RESULT_CANCELED) {
            System.out.println("one");
            Toast.makeText(this, "Item: " +  RESULT_CANCELED, Toast.LENGTH_SHORT).show();
        } else {
            System.out.println("two");
            Toast.makeText(this, "Item: " + -1, Toast.LENGTH_SHORT).show();
            discoverFlag= true;
        }
    }
}

Atleast the discovery user interface should show.But it is not showing. I think I need to pass an intent while creating Bluetooth object.How to do that? I have added Activity class because I saw it in an example code. In normal class bluetooth functions are not getting implemented. It shows compiler errors.

manifest file

    <?xml version="1.0" encoding="utf-8"?>
    <manifest xmlns:android="http://schemas.android.com/apk/res/android"
        package="com.example.root.securityalert">

        <application
            android:allowBackup="true"
            android:icon="@mipmap/ic_launcher"
            android:label="@string/app_name"
            android:roundIcon="@mipmap/ic_launcher_round"
            android:supportsRtl="true"
            android:theme="@style/AppTheme">
            <activity android:name=".MainActivity">
                <intent-filter>
                    <action android:name="android.intent.action.MAIN" />

                    <category android:name="android.intent.category.LAUNCHER" />
                </intent-filter>
            </activity>
<activity android:label="@string/app_name" android:name="BlueTooth"/>
        </application>
        <uses-permission android:name="android.permission.BLUETOOTH" />
        <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
        <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />

    </manifest>

I fixed the code. Now it launches the intent. But I have another problem, launching activity creates a new UI which I do not want.I want to use the previous UI of ListFragment class. So, what should I extend the BlueTooth class from? using plain BlueTooth class gives compile errors at 1.this.registerReceiver(mReceiver, ifilter); and 2.startActivityForResult(discoverableIntent,0); 3.@Override public void onActivityResult(int requestCode, int resultCode, Intent intent)