Fehler: "die Methode getText() muss aufgerufen werden, aus der UI-thread, derzeit abgeleitete thread-worker."

Während der Arbeit am Projekt bekomme ich eine Fehlermeldung auf die folgende Aktivität.
1. Login.java
auf die folgende Zeile von code.

Zeile: "String username = user.getText().toString();"
Fehler: "die Methode getText() muss aufgerufen werden, aus der UI-thread, derzeit abgeleitete thread-worker."

Ist meine ganze Tätigkeit Code.

package com.example.mysqltest;

import java.util.ArrayList;
import java.util.List;

import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class Login extends Activity implements OnClickListener {

    private EditText user, pass;
    private Button mSubmit, mRegister;

    //Progress Dialog
    private ProgressDialog pDialog;

    //JSON parser class
    JSONParser jsonParser = new JSONParser();

    //php login script location:

    //localhost :
    //testing on your device
    //put your local ip instead,  on windows, run CMD > ipconfig
    //or in mac's terminal type ifconfig and look for the ip under en0 or en1
    //private static final String LOGIN_URL = "http://xxx.xxx.x.x:1234/webservice/login.php";



    //testing from a real server:
    //private static final String LOGIN_URL = "http://www.example.com/webservice/login.php";

    //JSON element ids from repsonse of php script:
    private static final String TAG_SUCCESS = "success";
    private static final String TAG_MESSAGE = "message";

    public static String username;
    public static String password;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        //TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);

        //setup input fields
        user = (EditText) findViewById(R.id.username);
        pass = (EditText) findViewById(R.id.password);

        //setup buttons
        mSubmit = (Button) findViewById(R.id.login);
        mRegister = (Button) findViewById(R.id.register);

        //register listeners
        mSubmit.setOnClickListener(this);
        mRegister.setOnClickListener(this);


    }

    @Override
    public void onClick(View v) {
        //TODO Auto-generated method stub
        switch (v.getId()) {
            case R.id.login:
                username = user.getText().toString();
                password = pass.getText().toString();
                new AttemptLogin().execute();
                break;
            case R.id.register:
                Intent i = new Intent(this, Register.class);
                startActivity(i);
                break;

            default:
                break;
        }
    }

    class AttemptLogin extends AsyncTask<String, String, String> {

        /**
         * Before starting background thread Show Progress Dialog
         */
        boolean failure = false;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(Login.this);
            pDialog.setMessage("Attempting login...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }

        @Override
        protected String doInBackground(String... args) {
            //TODO Auto-generated method stub
            //Check for success tag
            int success;

            try {
                //Building Parameters
                List<NameValuePair> params = new ArrayList<NameValuePair>();
                params.add(new BasicNameValuePair("username", username));
                params.add(new BasicNameValuePair("password", password));

                Log.d("request!", "starting");
                //getting product details by making HTTP request
                JSONObject json = jsonParser.makeHttpRequest(
                        LOGIN_URL, "POST", params);

                //check your log for json response
                Log.d("Login attempt", json.toString());

                //json success tag
                success = json.getInt(TAG_SUCCESS);
                if (success == 1) {
                    Log.d("Login Successful!", json.toString());
                    Intent i = new Intent(Login.this, ReadComments.class);
                    finish();
                    startActivity(i);
                    return json.getString(TAG_MESSAGE);
                } else {
                    Log.d("Login Failure!", json.getString(TAG_MESSAGE));
                    return json.getString(TAG_MESSAGE);

                }
            } catch (JSONException e) {
                e.printStackTrace();
            }

            return null;

        }

        /**
         * After completing background task Dismiss the progress dialog
         **/
        protected void onPostExecute(String file_url) {
            //dismiss the dialog once product deleted
            pDialog.dismiss();
            if (file_url != null) {
                Toast.makeText(Login.this, file_url, Toast.LENGTH_LONG).show();
            }

        }

    }

}