How null pointer exception can be removed

Question

I am trying to find the signal strength of Wifi but I m getting a null pointer exception. While fetching the network informatiopns like SSID etc. Can anyone suggest me a solution how to remove the null pointer exception.

enter code here:

public class MyReciever extends BroadcastReceiver{
    WifiManager wifi;
    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO Auto-generated method stub
        List<ScanResult> results=wifi.getScanResults();
        ScanResult bestSignal=null;

        for(ScanResult result:results)
        {
            if(bestSignal==null || WifiManager.compareSignalLevel(bestSignal.level, result.level)<0)
                bestSignal=result;
        }

        String message=String.format("%s networks found. %s is the strongest", results.size(),bestSignal.SSID);
        Toast.makeText(context, message, Toast.LENGTH_LONG).show();

        Log.d("Debug","onRecieve() message:" +message);
    }

}



public class MainActivity extends Activity {

    TextView textStatus;
    WifiManager wifi;
    BroadcastReceiver receiver;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textStatus=(TextView)findViewById(R.id.textStatus);

        wifi=(WifiManager)getSystemService(Context.WIFI_SERVICE);

        WifiInfo info=wifi.getConnectionInfo();
        textStatus.append("\n\nWifi Status: " +info.toString());

        List<WifiConfiguration> configs=wifi.getConfiguredNetworks();
        for(WifiConfiguration config:configs)
        {
            textStatus.append("\n\n" +config.toString());
        }

        if(receiver==null)
                receiver = new MyReciever();

        registerReceiver(receiver, new IntentFilter(
                WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
        Log.d("TAG", "onCreate()");
    }

    @Override
    public void onStop() {
        unregisterReceiver(receiver);
            super.onStop();
    }
    }

1. See the exception stacktrace in logcat. 2. Find the corresponding code line. 3. Look up the line in your code and figure out what is the null that is dereferenced there. 4. Edit the question to contain the additional information at least from steps 1 and 2. — laalto
– laalto, Commented Oct 21, 2013 at 10:20
10-21 06:23:52.851: E/AndroidRuntime(1045): FATAL EXCEPTION: main 10-21 06:23:52.851: E/AndroidRuntime(1045): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.wifi/com.example.wifi.MainActivity}: java.lang.NullPointerException 10-21 06:23:52.851: E/AndroidRuntime(1045): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211) 10-21 06:23:52.851: E/AndroidRuntime(1045): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261) — Dexter
– Dexter, Commented Oct 21, 2013 at 10:28

Jayasagar · Accepted Answer · 2013-10-21 10:29:23Z

1

Problem could be at String message=String.format("%s networks found. %s is the strongest", results.size(),bestSignal.SSID);

When there is no 'bestSignal' found, variable 'bestSignal' will be null and you are trying to execute bestSignal.SSID which might cause NPE.

Change you code like if (bestSignal != null) { String message=String.format("%s networks found. %s is the strongest", results.size(),bestSignal.SSID); }

Hope it helps :)

answered Oct 21, 2013 at 10:29

Jayasagar

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