¿Cuál es el propósito de la declaración de devolución en doInBackground () de ASynctask?

Este aspecto de mi sistema de inicio de sesión funciona muy bien si tengo la declaración de devolución establecida en 0 o 1, pero falla si utilizo null. Esto es todo adaptado de http://256design.com/blog/android-login-asynctask/ donde esta vuelta particular mira como se enumera debajo de mi propio código.

public LoginTask(Polling activity, ProgressDialog progressDialog) { this.activity = activity; this.progressDialog = progressDialog; } protected Integer doInBackground(String... arg0) { EditText userName = (EditText)activity.findViewById(R.id.emailEditText); EditText passwordEdit = (EditText)activity.findViewById(R.id.passEditText); String email = userName.getText().toString(); String password = passwordEdit.getText().toString(); UserFunctions userFunction = new UserFunctions(); JSONObject json = userFunction.loginUser(email, password); progressDialog.dismiss(); // check for login response //Log.v("test", Integer.toString(jsonParser.getResponseCode())); try { if (json.getString(KEY_SUCCESS) != null) { //loginErrorMsg.setText(""); //loginFragment.loginErrorMsg.setText("Success"); String res = json.getString(KEY_SUCCESS); if(Integer.parseInt(res) == 1){ //user successfully logged in // Store user details in SQLite Database DatabaseHandler db = new DatabaseHandler(activity.getApplicationContext()); JSONObject json_user = json.getJSONObject("user"); //Log.v("name", json_user.getString(KEY_NAME)); // Clear all previous data in database userFunction.logoutUser(activity.getApplicationContext()); db.addUser(json_user.getString(KEY_NAME), json_user.getString(KEY_EMAIL), json.getString(KEY_UID), json_user.getString(KEY_CREATED_AT)); // Close Login Screen //finish(); //loginErrorMsg = (TextView)activity.findViewById(R.id.loginErrorMsg); //loginErrorMsg.setText("logged in"); //passwordEdit.setText(""); }else{ // Error in login //progressDialog.setMessage("Incorrect username or password"); //loginErrorMsg.setText("Incorrect username/password"); } } } catch (NullPointerException e) { e.printStackTrace(); } catch (JSONException e) { e.printStackTrace(); } return 1; } 

El tutorial que he utilizado, eche un vistazo a responseCode:

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 protected Integer doInBackground(String... arg0) { String result = ""; int responseCode = 0; try { HttpClient client = new DefaultHttpClient(); HttpPost httppost = new HttpPost("http://www.256design.com/projectTransparency/project/headerLogin.php"); List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(); nameValuePairs.add(new BasicNameValuePair("emailAddress", arg0[0])); nameValuePairs.add(new BasicNameValuePair("password", arg0[1])); httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs)); int executeCount = 0; HttpResponse response; do { progressDialog.setMessage("Logging in.. ("+(executeCount+1)+"/5)"); // Execute HTTP Post Request executeCount++; response = client.execute(httppost); responseCode = response.getStatusLine().getStatusCode(); // If you want to see the response code, you can Log it // out here by calling: // Log.d("256 Design", "statusCode: " + responseCode) } while (executeCount < 5 && responseCode == 408); BufferedReader rd = new BufferedReader(new InputStreamReader( response.getEntity().getContent())); String line; while ((line = rd.readLine()) != null) { result = line.trim(); } id = Integer.parseInt(result); } catch (Exception e) { responseCode = 408; e.printStackTrace(); } return responseCode; } 

 if(headerCode == 202) activity.login(id); 

 protected class InitTask extends AsyncTask<Context, Integer, Integer> 

 @Override protected Integer doInBackground( Context... params ) { return super.doInBackground( params ) }