[Verständnisproblem] Bluetooth LE Geräte scannen - Scan klappt, Anzeige nicht

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothManager;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListView;
import java.util.ArrayList;


public class MainActivity extends Activity {

    private ListView list;
    private Handler mHandler;
    private boolean mScanning;
    private BluetoothAdapter mBluetoothAdapter;
    private LeDeviceAdapter mLeDeviceListAdapter;
    private ArrayList<String> bcnList;

    private BluetoothAdapter.LeScanCallback mLeScanCallback =
            new BluetoothAdapter.LeScanCallback() {

                @Override
                public void onLeScan(final BluetoothDevice device, int rssi, byte[] scanRecord) {
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            if (!bcnList.contains(device.getAddress())){
                                bcnList.add(device.getAddress());
                                mLeDeviceListAdapter.notifyDataSetChanged();
                            }
                        }
                    });
                }
            };

    private static final int SCAN_PERIOD = 5000;
    private static final int REQUEST_ENABLE_BT = 1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        bcnList = new ArrayList<String>();
        mHandler = new Handler();
        final BluetoothManager bluetoothManager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
        mBluetoothAdapter = bluetoothManager.getAdapter();
    }

    @Override
    protected void onResume() {
        super.onResume();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        switch (id){
            case R.id.scan:
                mLeDeviceListAdapter = new LeDeviceAdapter(this, bcnList);
                scanLeDevice(true);
                fillList();
                return true;
            case R.id.action_settings:
                return true;
            default:
                return super.onOptionsItemSelected(item);

        }
    }

    private void scanLeDevice(final boolean enable) {
        if (enable) {
            // Stops scanning after a pre-defined scan period.
            mHandler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    mScanning = false;
                    mBluetoothAdapter.stopLeScan(mLeScanCallback);
                    invalidateOptionsMenu();
                }
            }, SCAN_PERIOD);

            mScanning = true;
            mBluetoothAdapter.startLeScan(mLeScanCallback);
        } else {
            mScanning = false;
            mBluetoothAdapter.stopLeScan(mLeScanCallback);
        }
        invalidateOptionsMenu();
    }

    private boolean fillList(){
        list = (ListView) findViewById(R.id.list);
        list.setAdapter(mLeDeviceListAdapter);
        return true;
    }
}

import android.app.Activity;
import android.content.Context;
import android.text.Layout;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

import java.util.ArrayList;

/**
 * Created by miho on 08.09.14.
 */
public class LeDeviceAdapter extends ArrayAdapter<String> {

    private ArrayList<String> bcnList;
    private Activity context;

    public LeDeviceAdapter(Activity context, ArrayList<String> addresses) {
        super(context, R.layout.list_single);
        this.context = context;
        bcnList = addresses;
    }


    @Override
    public View getView(int position, View view, ViewGroup parent){
        LayoutInflater inflater = context.getLayoutInflater();
        View row = inflater.inflate(R.layout.list_single, null, true);
        TextView address = (TextView) row.findViewById(R.id.txt);
        address.setText(bcnList.get(position));
        return row;
    }
}