onPostExecute只被调用一次

Question

执行AsyncTask时遇到问题：onPostExecute（）方法只执行一次。第二次没有更新。

记录：

05-31 23:15:35.261 31682-32136/com.stimulus D/result45: Qu'est ce que c'est ?
05-31 23:15:35.301 31682-31682/com.stimulus D/result50: Qu'est ce que c'est ?
05-31 23:15:38.201 31682-31878/com.stimulus D/result45: C'est quoi ?
05-31 23:15:38.261 31682-31682/com.stimulus D/result50: Qu'est ce que c'est ?

代码：

class NextQuestionChooseAsync extends AsyncTask<String, Void, ArrayList<String>> {

        private Dialog loadingDialog;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            loadingDialog = ProgressDialog.show(QuestionActivity.this, "Please wait", "Loading...");
        }

        @Override
        protected ArrayList<String> doInBackground(String... params) {

            InputStream is = null;


            email = (String) getIntent().getSerializableExtra("email");
            password = (String) getIntent().getSerializableExtra("password");
            idSession = (int) getIntent().getSerializableExtra("idSession");
            String json = null;
            String result = null;
            String question = null;

            try {
                //Http request to communicate with our system
                HttpClient httpClient = new DefaultHttpClient();

                List<BasicNameValuePair> parameters = new LinkedList<BasicNameValuePair>();
                parameters.add(new BasicNameValuePair("idsession", String.valueOf(idSession)));


                HttpGet httpGet = new HttpGet();
                URI website = new URI("http://192.168.1.33:5001/nextquestion" + "?"+ URLEncodedUtils.format(parameters, "utf-8"));
                httpGet.setURI(website);

                String base64EncodedCredentials = Base64.encodeToString(
                        (email + ":" + password).getBytes(),
                        Base64.NO_WRAP);

                Log.d("test",base64EncodedCredentials);

                httpGet.setHeader("Authorization", "Basic " + base64EncodedCredentials);

                HttpResponse response = httpClient.execute(httpGet);

                statusCode = response.getStatusLine().getStatusCode();

                HttpEntity entity = response.getEntity();
                is = entity.getContent();

                BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"), 8);
                StringBuilder sb = new StringBuilder();

                String line = null;
                while ((line = reader.readLine()) != null) {
                    sb.append(line + "\n");
                }
                result = sb.toString();

                Log.d("result1", result);

                //Manage JSON result
                JSONObject jsonObject = new JSONObject(result);

                question = jsonObject.getString("question");

                Log.d("result45",question);

                questionInformation.add(question);

            } catch (ClientProtocolException e) {
                e.printStackTrace();
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (JSONException e) {
                e.printStackTrace();
            } catch (URISyntaxException e) {
                e.printStackTrace();
            }

            return questionInformation;

        }

        @Override
        protected void onPostExecute(ArrayList<String> status) {
            loadingDialog.dismiss();
            String question = questionInformation.get(0);

            Log.d("result50",question);
            tv_title_question.setText(question);

        }
    }
    NextQuestionChooseAsync nqca = new NextQuestionChooseAsync();
    nqca.execute();
}

为什么第二次方法onPostExecute（）中的值问题没有改变？

谢谢你的帮助。