Android arrayadapter without specifying object

i want to use listview with ArrayAdapter

After scanning for WiFi, the code for broadcast receiver is as below

public void onReceive(Context context, Intent intent) {
        // TODO Auto-generated method stub
        scanResultDevices.notifyDataSetInvalidated();
        wifiResults = wm.getScanResults();
        scanResultDevices = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1);
        scanResultAdapter = new ArrayAdapter<ScanResult>(getApplicationContext(),android.R.layout.simple_list_item_1);
        Log.e("inside","BD REceiver");
        if(wifiResults != null){
            for(ScanResult s : wifiResults){
                scanResultAdapter.add(s);
                scanResultDevices.add(s.SSID);
            }
        scanResult.setAdapter(scanResultDevices);
        scanResultDevices.notifyDataSetChanged();
        }
        unregisterReceiver(scanComp);
    }

But this shows null pointer exception at scanResult.setAdapter(scanResultDevices)

I know how to use new ArrayAdapter<T>(context, textViewResourceId, objects). But in this specific case i want to try new ArrayAdapter<T>(context, textViewResourceId). If what i am trying is not possible, then how can i do it correctly?

EDIT:

Updated code

 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_test);
    View v = findViewById(R.id.dialogtitle);
    scanResult = (ListView) findViewById(R.id.scanResult);

    //scanResult.setAdapter(scanResultDevices);

    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setMessage("Scan For Device").setCustomTitle(v).setPositiveButton("SCan",this).create();
    builder.show();
}

The code for onClick:

@Override
public void onClick(DialogInterface dialog, int which) {
    // TODO Auto-generated method stub
    wm = (WifiManager) getSystemService(WIFI_SERVICE);
    if(!wm.isWifiEnabled()){
        wm.setWifiEnabled(true);
        Toast.makeText(getApplicationContext(), "Turning on Wifi", Toast.LENGTH_SHORT);
        Log.e("Wifi","Not-on!Enabling");
    }
    MyDialogFragment alert = new MyDialogFragment();
    alert.show(getFragmentManager(), "SCAN_DIALOG");
    wm.startScan();

    registerReceiver(scanComp, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));


//  if(wifiResults.isEmpty())

}