public void Running() {
new Handler().postDelayed(new Runnable() {
                @Override
                public void run() {
                    tv1.setText("counter :   " + time1);
                    time1++;
                    Scan_number++;
                    mwifiManager.startScan();
                    periodic_recieving_wifi_signals();
                    Running();
                }
            }, 1000);}

public void periodic_recieving_wifi_signals() {

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && checkSelfPermission(android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        requestPermissions(new String[]{Manifest.permission.ACCESS_COARSE_LOCATION}, PERMISSIONS_REQUEST_CODE_ACCESS_COARSE_LOCATION);

    } else {
        //flag1 = false;

        registerReceiver(new BroadcastReceiver() {

            @Override
            public void onReceive(Context context, Intent intent) {

                //tv2.setText("Each scan period is   : " + results);
                results = mwifiManager.getScanResults();
                size = results.size();// number of the elements in the list


            }
        }, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));

    }}