Network on MainThread Exception (One app is working, other one throwing exception)

Question

I am having an awkward issue (may be for me). I am using the timer to perform Tcp listner and socket programming. I am opening a socket to listen any data present on the port sent from another Android device (working correctly) regularly. I have created 2 applications to test the data receiving, one is just dummy and second is my main application. I am getting exception in my main application but not in the dummy application.

Exception is : android.os.NetworkonMainThreadException

The code is exactly same in both apps here it is

onCreate() contains

timer2 = new Timer();
        timer2.schedule(new TimerTask() {           
            @Override
            public void run() {
                TimerMethod();
            }

        }, 0, 1000);

TimerMethod() is as follows

private void TimerMethod()
    {
        this.runOnUiThread(Timer_Tick);
    }

Timer_Tick is:

private Runnable Timer_Tick = new Runnable() {
        public void run() {
            try
            {
                runTcpServer();
            }

            catch(Exception a)
            {
                TextView tv = (TextView) findViewById(R.id.textView1);
                tv.setText(a.toString());
            }

        }
    };

And the main Tcp method to listen the data on the port

public void runTcpServer()
    {
        ServerSocket ss = null;
        try {
            ss = new ServerSocket(TCP_SERVER_PORT);
            //ss.setSoTimeout(10000);
            //accept connections
            Socket s = ss.accept();
            BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
            BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
            //receive a message
            String incomingMsg = in.readLine() + System.getProperty("line.separator");

            TextView tv= (TextView) findViewById(R.id.textView2);
            //Log.d("TcpServer", "received: " + incomingMsg);
            tv.append(incomingMsg);
            //send a message
            String outgoingMsg = "goodbye from port " + TCP_SERVER_PORT + System.getProperty("line.separator");
            out.write(outgoingMsg);
            out.flush();
            Log.d("TcpServer", "sent: " + outgoingMsg);
            //textDisplay.append("sent: " + outgoingMsg);

            //SystemClock.sleep(5000);
            s.close();
        } catch (InterruptedIOException e) {
            //if timeout occurs
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } 
        finally {
            if (ss != null) {
                try {
                    ss.close();
                } catch (IOException e) {
                    Log.d("Error",e.toString());
                }
            }
       }
    }

The exception i am getting is when i am calling the runTcpServer() in Timer_Tick

Arun C · Answer 1 · 2013-06-19T05:32:36.740

2

This is the error

   this.runOnUiThread(Timer_Tick);

Never run network task in UI thread(Main thread)!

Or use this to enable network task in UI thread, but it is not fair

StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();

StrictMode.setThreadPolicy(policy);

edited Jun 19 '13 at 05:32

answered Jun 19 '13 at 05:25

Arun C

9,035
2
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Why it is running in the dummy application created for just testing ? – Jibran Khan Jun 19 '13 at 05:25
Network operations can involve unpredictable delays. To prevent this from causing a poor user experience, always perform network operations on a separate thread from the UI. The AsyncTask class provides one of the simplest ways to fire off a new task from the UI thread. – Arun C Jun 19 '13 at 05:28
to enable network task in UI thread See edit – Arun C Jun 19 '13 at 05:33

score 1 · Accepted Answer · answered Jun 19 '13 at 05:25

1

You are running network related operation on the main ui thread. You should use Asynctask or create a new thread.

http://developer.android.com/reference/android/os/NetworkOnMainThreadException.html

Check the above link

I suggest you use asynctask.

http://developer.android.com/reference/android/os/AsyncTask.html

Use Asynctask and move your runTcpServer(). Also remember you cannot update ui from a background thread. You will have to use runOnUiThread or update ui in onPostExecute

Move all your network related operation to doInbackground(). Move the below to onPostExecute(). You can return the result of computation in doInbackground(). Based on the result update ui in onPostExecute

    TextView tv= (TextView) findViewById(R.id.textView2);
        //Log.d("TcpServer", "received: " + incomingMsg);
    tv.append(incomingMsg);

answered Jun 19 '13 at 05:25

Raghunandan

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Why it is running in the dummy application created for just testing ? the data received is correct. – Jibran Khan Jun 19 '13 at 05:27
What you mean by dummy application created? – Raghunandan Jun 19 '13 at 05:28
A test app with same procedure as mentioned above is working correctly. – Jibran Khan Jun 19 '13 at 05:29
did you test it on a real device and on what version check the first link – Raghunandan Jun 19 '13 at 05:30
also why do you require a timer? – Raghunandan Jun 19 '13 at 05:33
Yes tested on the real device. Its minsdk target is 4 (the one working). – Jibran Khan Jun 19 '13 at 05:36
Need timer to keep running the tcp server to check the data on the port – Jibran Khan Jun 19 '13 at 05:37
`NetworkOnMainThreadException` only thrown for applications targeting the Honeycomb SDK or higher. pls check the first link in the answer – Raghunandan Jun 19 '13 at 05:38

Yahya Arshad · Answer 3 · 2013-06-19T05:45:03.837

The error is visible you are executing timer on UI Thread this.runOnUiThread(Timer_Tick);, Network operation should always be performed on Worker Thread, instead just do new Thread(new Timer_Tick()).start();, executing network operation(as they are long running process) cause UI to not respond till network operation is complete.

Addition I saw this is android question, You can use AsyncTask See http://developer.android.com/reference/android/os/AsyncTask.html After Android OS 2.3 Network Operation on UI thread is not allowed

Network on MainThread Exception (One app is working, other one throwing exception)

3 Answers3