How to Store in Global Variable from local variable?

Question

At the last Toast, It will print blank Toast.Why? I am passing local variable to a global variable and thus printed it. Why Java does not allow this? And What is the Solution Of this?

Here is the code...

String sb_temp=" ";  //global variable


public void getsortedsignal()
{

    final WifiManager wm=(WifiManager)getApplicationContext().getSystemService(Context.WIFI_SERVICE);

    if(wm.isWifiEnabled()==false) {
        Toast.makeText(getApplicationContext(), "Wifi Is Disabled.. Please Enable it", Toast.LENGTH_LONG).show();
        wm.setWifiEnabled(true);
    }

    registerReceiver(new BroadcastReceiver() {


        @Override
        public void onReceive(Context context, Intent intent) {
            StringBuilder sb = new StringBuilder();

            wm.startScan();

            scanResults = wm.getScanResults();

            //Making it in Asencending Order
            Comparator<ScanResult> comparator = new Comparator<ScanResult>() {
                @Override
                public int compare(ScanResult lhs, ScanResult rhs) {
                    return (lhs.level > rhs.level ? -1 : (lhs.level == rhs.level ? 0 : 1));
                }
            };

            Collections.sort(scanResults, comparator);

            //Exact 5 Ap's Values
            for (int i = 0; i < 5; i++) {

                sb.append(scanResults.get(i).SSID + "--").toString();
                sb.append(scanResults.get(i).BSSID + "--").toString();
                sb.append((-1 * scanResults.get(i).level) + "\n").toString();
            }


            sb_temp=sb.toString();

            //Toast.makeText(getApplicationContext(), sb_temp, Toast.LENGTH_SHORT).show();

        }

    }, new IntentFilter(WifiManager.RSSI_CHANGED_ACTION));

    Toast.makeText(getApplicationContext(), sb_temp, Toast.LENGTH_SHORT).show();   //Problem is Here!!!!!!!!

}

Answer 1

The problem is before your global variable gets updated the Toast is called. Receiving happens on a background thread whereas Toast is being displayed on main Thread. If you want to display toast then you can put Toast in the receiver itself.

Moreover there is a chance that your global variable is null if there is some error while receiving

Also you can update global variable using a function and then calling a toast inside it. Like:

    for (int i = 0; i < 5; i++) {

        sb.append(scanResults.get(i).SSID + "--").toString();
        sb.append(scanResults.get(i).BSSID + "--").toString();
        sb.append((-1 * scanResults.get(i).level) + "\n").toString();
    }


    updateGloablString(sb);

......

private void updateGlobalString(String sb){
 sb_temp=sb.toString();
Toast.makeText(getApplicationContext(), sb_temp, Toast.LENGTH_SHORT).show();

}