Fatal exception in main thread

Question

I am new to android. My project is related to networking. I am getting this error FATAL EXCEPTION: main

android.os.NetworkOnMainThreadException
at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java1133)

... ...

My code is :

package com.example.simpleclientactivity;
    import java.io.IOException;
    import java.io.PrintWriter;
    import java.net.Socket;
    import java.net.UnknownHostException;

    import android.app.Activity;
    import android.content.Context;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.Button;
    import android.widget.EditText;
    import android.widget.Toast;

    public class SimpleClientActivity extends Activity {

     private Socket client;
     private PrintWriter printwriter;
     private EditText textField1;
     private Button button;
     private String messsage;

     @Override
     public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);

      textField1 = (EditText) findViewById(R.id.editText1); //reference to the text field
      button = (Button) findViewById(R.id.button1);   //reference to the send button

      //Button press event listener
      button.setOnClickListener(new View.OnClickListener() {

       public void onClick(View v) {

          Context context = getApplicationContext();
          CharSequence text = "Hello toast!";
          int duration = Toast.LENGTH_SHORT;

          Toast toast = Toast.makeText(context, text, duration);
          toast.show();
          messsage = textField1.getText().toString(); //get the text message on the text field      
          textField1.setText("");      //Reset the text field to blank

          try {

                 client = new Socket("10.0.2.2", 4444);  //connect to server
                 printwriter = new PrintWriter(client.getOutputStream(),true);
                 printwriter.write(messsage);  //write the message to output stream

                 printwriter.flush();
                 printwriter.close();
                 client.close();   //closing the connection

                } catch (UnknownHostException e) {
                 e.printStackTrace();
                } catch (IOException e) {
                 e.printStackTrace();
                }
        }
      });

     }
    }

Here is main.xml code

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <EditText
        android:id="@+id/editText1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"`enter code here`
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="83dp"
        android:ems="10"
        android:text="Client" >

        <requestFocus />
    </EditText>

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/editText1"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="53dp"
        android:text="Send" />

</RelativeLayout>

It's not even displaying the toast message after clicking the button. However it's showing error in android.os.NetworkOnMainThreadException.

you cant connect to internet in `UI` Thread, use `AsyncTask` class — Shayan Pourvatan, Dec 19 '13 at 06:44
it would have taken less time to search an answer for this then to post this question... — Vikram Singh, Dec 19 '13 at 07:08

Hariharan · Accepted Answer · 2013-12-20T04:27:26.210

Try this..

This exception is thrown when an application attempts to perform a networking operation on its main thread

 button.setOnClickListener(new View.OnClickListener() {

       public void onClick(View v) {

          Context context = getApplicationContext();
          CharSequence text = "Hello toast!";
          int duration = Toast.LENGTH_SHORT;

          Toast toast = Toast.makeText(context, text, duration);
          toast.show();
          messsage = textField1.getText().toString(); //get the text message on the text field      
          textField1.setText("");      //Reset the text field to blank

            new MyClass().execute(messsage);


        }
      });

MyClass.class AsyncTask

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

    private Exception exception;

    protected String doInBackground(String... messsage) {
        try {

                 client = new Socket("10.0.2.2", 4444);  //connect to server
                 printwriter = new PrintWriter(client.getOutputStream(),true);
                 printwriter.write(messsage);  //write the message to output stream

                 printwriter.flush();
                 printwriter.close();
                 client.close();   //closing the connection

                } catch (UnknownHostException e) {
                 e.printStackTrace();
                } catch (IOException e) {
                 e.printStackTrace();
                }
    }

    protected void onPostExecute(String result) {
        // TODO: check this.exception 
        // TODO: do something with the feed
    }
}

You cannot perform network IO on the UI thread on Honeycomb. Technically it is possible on earlier versions of Android, but is a really bad idea as it will cause your app to stop responding, and can result in the OS killing your app for being badly behaved. You'll need to run a background process or use AsyncTask to perform your network transaction on a background thread.

There is an article about Painless Threading on the Android developer site which is a good introduction to this, and will provide you with much better depth of answer than can be realistically provided here.

score 0 · Answer 2 · answered Dec 19 '13 at 06:47

0

You have to put your code that access the internet on a thread

new Thread(new Runnable(){
  @Override
  public void run(){
    //your code that access internet here
  }
}).start();

answered Dec 19 '13 at 06:47

Rick Royd Aban

904
6
33

score 0 · Answer 3 · answered Dec 19 '13 at 06:52

try this code

   package com.example.simpleclientactivity;
   import java.io.IOException;
  import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class SimpleClientActivity extends Activity {

 private Socket client;
 private PrintWriter printwriter;
 private EditText textField1;
 private Button button;
 private String messsage;

 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);

  textField1 = (EditText) findViewById(R.id.editText1); //reference to the text field
  button = (Button) findViewById(R.id.button1);   //reference to the send button

  //Button press event listener
  button.setOnClickListener(new View.OnClickListener() {

   public void onClick(View v) {

      Context context = getApplicationContext();
      CharSequence text = "Hello toast!";
      int duration = Toast.LENGTH_SHORT;

      Toast toast = Toast.makeText(context, text, duration);
      toast.show();
      messsage = textField1.getText().toString(); //get the text message on the text field      
      textField1.setText("");      //Reset the text field to blank

    new GetCategory().execute(message);
    }
  });

 }


    //add inner class

   class GetCategory extends AsyncTask<Void, Void, ArrayList<AbstractDetail>>{



    protected  ArrayList<AbstractDetail>  doInBackground(String... messsage) {
        try {

             client = new Socket("10.0.2.2", 4444);  //connect to server
             printwriter = new PrintWriter(client.getOutputStream(),true);
             printwriter.write(messsage);  //write the message to output stream

             printwriter.flush();
             printwriter.close();
             client.close();   //closing the connection

            } catch (UnknownHostException e) {
             e.printStackTrace();
            } catch (IOException e) {
             e.printStackTrace();
            }
        return null;

    }

    protected void onPostExecute(ArrayList<AbstractDetail> result)
    {


        }

    }


}






}

score 0 · Answer 4 · answered Dec 19 '13 at 07:29

Problem

You can not access network over UI thread. You are accessing Network through UI thread that's why you are getting NetworkOnMainThreadException.

Solution

Create new thread and access Network over that Thread. OR
Use AsyncTask to do network related work on doInBackgroung() and for updating UI onPostExecute().

Fatal exception in main thread

4 Answers4

try this code