如何设置wifi扫描？

Question

我试图在我的设备上设置wifi扫描。这是我正在使用的一段代码：

  public void start() {
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION);
        fragmentActivity.registerReceiver(mWifiScanReceiver, intentFilter);
        boolean test = wifiManager.startScan();
        //the rest of the code
  }

和：

private final BroadcastReceiver mWifiScanReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context c, Intent intent) {
            // This condition is not necessary if you listen to only one action
            if (intent.getAction().equals(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)) {
                getSSIDs();
            }
        }



        private void getSSIDs() {
            if(!wifiManager.isWifiEnabled()){
                Log.i(TAG, "Enabling wi-fi...");
                if (wifiManager.setWifiEnabled(true)) {
                    Log.i(TAG, "Wi-fi enabled");
                } else {
                    Log.w(TAG, "Wi-fi could not be enabled!");
                    return;
                }
            }
            int count = 0;
            while(!wifiManager.isWifiEnabled()){
                if(count >= 10){
                    Log.i(TAG, "Took too long to enable wi-fi, quitting");
                    return;
                }
                Log.i(TAG, "Still waiting for wi-fi to enable...");
                try {
                    Thread.sleep(1000L);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                count++;
            }
            List<ScanResult> networkList = wifiManager.getScanResults();
            for (ScanResult s : networkList) {
                if (s.SSID.length() > 0 && !ssids.contains(s.SSID)) {
                    ssids.add(s.SSID);
                }
            }
        }
    };

问题是当我第一次运行程序时扫描结果为空。它可能是并发问题，因为第二次设置扫描。你知道如何正确地做到这一点吗？