Search for Wi-Fi networks and list them on Android

I can not find the problem, there are no mistakes but it does not work for me.

public class ConfigWifiBT extends Activity implements View.OnClickListener {

    WifiManager wifi;
    ListView lv;
    Button buttonScan;
    int size = 0;
    List<ScanResult> results;

    ListView IdLista;
    private ArrayAdapter mPairedDevicesArrayAdapter;


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

        buttonScan = (Button) findViewById(R.id.scan);
        buttonScan.setOnClickListener(this);


        wifi = (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);
        if (wifi.isWifiEnabled() == false)
        {
            Toast.makeText(getApplicationContext(), "wifi is disabled..making it enabled", Toast.LENGTH_LONG).show();
            wifi.setWifiEnabled(true);
        }

        mPairedDevicesArrayAdapter = new ArrayAdapter(this, R.layout.activity_dispositivos_bt);
        IdLista = (ListView) findViewById(R.id.wifilist);
        IdLista.setAdapter(mPairedDevicesArrayAdapter);
        IdLista.setOnItemClickListener(mDeviceClickListener);

        scanWifiNetworks();
    }

    private AdapterView.OnItemClickListener mDeviceClickListener = new AdapterView.OnItemClickListener() {
        public void onItemClick(AdapterView av, View v, int arg2, long arg3) {

            String info = ((TextView) v).getText().toString();
            String address = info.substring(info.length() - 17);
            Log.d("Wifi info:",info+" - "+address);
        }
    };

    public void onClick(View view)
    {
        scanWifiNetworks();
    }

    private void scanWifiNetworks(){
        registerReceiver(wifi_receiver, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
        wifi.startScan();
        Log.d("WifScanner1", "scanWifiNetworks");
        Toast.makeText(this, "Scanning....", Toast.LENGTH_SHORT).show();
    }

    BroadcastReceiver wifi_receiver= new BroadcastReceiver()
    {
        @Override
        public void onReceive(Context c, Intent intent)
        {
            Log.d("WifScanner2", "onReceive");
            results = wifi.getScanResults();
            size = results.size();
            unregisterReceiver(this);

            try
            {
                while (size >= 0)
                {
                    size--;
                    mPairedDevicesArrayAdapter.add(results.get(size).SSID);
                }
            }
            catch (Exception e)
            {
                Log.w("WifScanner3", "Exception: "+e);
            }
        }
    };
}

Layout, ignore the name of the same, activity_bug_devices:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:padding="10dp"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:id="@+id/wifilist"
        android:layout_width="match_parent"
        android:layout_height="312dp"
        android:layout_weight="0.97" />


    <Button
        android:id="@+id/scan"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:layout_gravity="bottom"
        android:layout_margin="15dp"
        android:background="@android:color/holo_green_light"
        android:text="Scan Again" />
</LinearLayout>

The log that appears in Logcat is: W / WifScanner3: Exception: java.lang.ArrayIndexOutOfBoundsException: length = 0; index = -1