Android :: Code For Scanning WiFi Network - Null Point Exception

I am trying out this code for scanning wifi networks but getting null pointer exception not sure what problem I registered all permission in manifest.

IntentFilter i = new IntentFilter();
i.addAction(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION);
registerReceiver(new BroadcastReceiver(){
@Override
public void onReceive(Context context, Intent intent) {
// TODO Auto-generated method stub
Log.i(TAG, "opening wifimanager");
WifiManager mWifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
mWifiManager.getScanResults();
} } ,i);
mWifiManager.startScan();