What is an android.os.NetworkOnMainThreadException

May be this can help you solving your issue

@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.main);       
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
        StrictMode.setThreadPolicy(policy);
    }

NetworkOnMainThreadException: The exception that is thrown when an application attempts to perform a networking operation on its main thread.

You can create an AsyncTask class as follows:

private class MyAsyncTask extends AsyncTask<Void, Void, Void>
{

    @Override
    protected void onPostExecute(Void result) {
        //Task you want to do on UIThread after completing Network operation
        //onPostExecute is called after doInBackground finishes its task.
    }

    @Override
    protected Void doInBackground(Void... params) {
       //Do your network operation here
        return null;
    }
}

Also, don't forget to call the doInBackground() function, which can be easily called by using MyAsyncTask.execute(). Hope this helps..

This work for me.

Please try to ip address inside of localhost

Android Permission:

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Class RetrieveFeedTask code:

class RetreiveFeedTask extends AsyncTask<String, Void, Void> {

  private Exception exception;

  protected Void doInBackground(String... datas) {
     try {
        Socket s = new Socket("10.10.10.46", 8888);

        DataOutputStream dout = new DataOutputStream(s.getOutputStream());
        for (String string : datas) {
           dout.writeUTF(string);
        }

        dout.flush();
        dout.close();
        s.close();
     } catch (Exception e) {
        this.exception = e;
     }
     return null;
  }

  protected void onPostExecute(Void void1) {
     // do nothing;
  }

  public RetreiveFeedTask() {
  }

  public Exception getException() {
     return exception;
  }

}


 @Override
 public void onClick(View v) {
     switch (v.getId()) {
     case R.id.btn:

        RetreiveFeedTask feedTask = new RetreiveFeedTask();
        feedTask.execute(new String[] { "hello", "hello" });
        if (feedTask.getException() != null) {
           Log.d(TAG, feedTask.getException().toString());
        }
  }

Always use Threads, preferably AsyncTask, to perform network or any other time taking operations . Read this.

P.S. A little search on Google could give you hundreds of results.

Try this AsyncTask tutorial. For best practice use Async methods.

for simple try this code in onCreate method

StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder().detectAll().penaltyLog().penaltyDeath().build());
StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder().detectAll().penaltyLog().penaltyDeath().build());

But sometimes it is difficult to remember to make all the right things in your application during development. That is were StrictMode comes in. It allows to setup policies in your application to avoid doing incorrect things. For example the following setup will crash your application if it violates some of the Android policies. StrictMode should only be used during development and not in your live application.

Better avoid using StrictMode, go for using AsyncTask method.