Android应用程序上的奇怪错误

Question

我不知道该怎么称呼这个错误。我的应用程序使用自编写的共享首选项类。运行我的应用程序几次后，我的远程服务器无法检索到任何内容。我将发布我的共享首选项和一个我的异步任务。当应用程序没有检索任何内容时，logcat中没有错误。

共享偏好设置课程：

public class SharedPreferences{

    static final String PREF_USER_NAME = "username";
    static final String PREF_USER_ID = "userid";

    static android.content.SharedPreferences getSharedPreferences(Context ctx) {
        return PreferenceManager.getDefaultSharedPreferences(ctx);
    }

    public static void setUserName(Context ctx, String userName) 
    {
        Editor editor = getSharedPreferences(ctx).edit();
        editor.putString(PREF_USER_NAME, userName);
        editor.commit();
    }

    public static void setUserId(Context ctx, String userId)
    {
        Editor editor = getSharedPreferences(ctx).edit();
        editor.putString(PREF_USER_ID, userId);
        editor.commit();
    }

    public static String getUserName(Context ctx)
    {
        return getSharedPreferences(ctx).getString(PREF_USER_NAME, "");
    }

    public static String getUserId(Context ctx)
    {
        return getSharedPreferences(ctx).getString(PREF_USER_ID, "");
    }

    public static void clearUserName(Context ctx) 
    {
        Editor editor = getSharedPreferences(ctx).edit();
        editor.clear(); //clear all stored data
        editor.commit();
    }
}

项目检索异步任务：

public class GetEventsAsyncTask extends AsyncTask<String, Integer, Boolean>{

    ProgressDialog progressDialog;
    MainActivity activityMain;
    List<Event> eventList = new ArrayList<Event>();
    MyDbAdapter db;

    public GetEventsAsyncTask(MainActivity parent)
    {
        activityMain = parent;
    }

     @Override
        protected void onPreExecute() {

//          progressDialog = null;
//          
//           if (progressDialog == null) 
//           {
//                 progressDialog = new ProgressDialog(activityMain);
//                 progressDialog.setMessage("download events, please wait...");
//                 progressDialog.show();
//                 progressDialog.setCanceledOnTouchOutside(false);
//                 progressDialog.setCancelable(false);
//           }   
        }

          @Override
          protected Boolean doInBackground(String... params) {
            // TODO Auto-generated method stub
                Boolean error = false;
                try {
                    error = postData(params[0]);
                } catch (JSONException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                return error;
          }

          protected void onPostExecute(Boolean error){          
                 /* if (progressDialog.isShowing()) {
                      progressDialog.dismiss();
                      progressDialog = null;
                  } */
                  if(error==true)
                  {
                      Log.i("GetEvents", "Error at get events");
                      activityMain.errorOccured();
                  }
                  else
                  {
                      Log.i("onPostExecute:eventlist.count",String.valueOf(eventList.size()));
                      MainActivity.myDB.removeAllEvents();
                      for(int i=0;i<eventList.size();i++)
                      {
                          MainActivity.myDB.insertEventEntry(eventList.get(i));
                      }
                      activityMain.downloadEventsSuccess(eventList);
//                    progressDialog.dismiss();

                  }

          } 

          protected void onProgressUpdate(Integer... progress){
          }


        public Boolean postData(String user_id) throws JSONException {

            Boolean error = false;
            HttpClient httpclient = new DefaultHttpClient();
          // specify the URL you want to post to

            try {
                Log.i("GetEvents", user_id);
                HttpGet httpget = new HttpGet(Constants.HOST_NAME+"/"+Constants.SERVICE_NAME+"/api/Event?userId=" + user_id);
                BufferedReader reader;
                StringBuffer sb;
                String line = "";
                String NL="";
                String json;
                HttpResponse response = httpclient.execute(httpget);

                if(response.getStatusLine().getStatusCode()==200)
                {
                    reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent(), "UTF-8"));

                     sb = new StringBuffer("");
                     line = "";
                     NL = System.getProperty("line.separator");

                    while ((line = reader.readLine()) != null)
                    {
                        sb.append(line + NL);
                    }

                    reader.close();
                    json = sb.toString();

                    Log.i("event json",json);
                    try
                    {
                        JSONArray jsonArray = new JSONArray(json);   

                        for (int i = 0, length = jsonArray.length(); i < length; i++)
                        {
                            JSONObject attribute = jsonArray.getJSONObject(i);
                            Log.i("EventsAsync", attribute.toString(i));
                            Event eventObj =  new Event(); 
                            eventObj.setEvent_id(attribute.getString("event_id"));
                            eventObj.setEvent_title(attribute.getString("event_title"));
                            eventObj.setEvent_desc(attribute.getString("event_desc"));
                            eventObj.setStart_date(attribute.getString("start_date"));
                            eventObj.setEnd_date(attribute.getString("end_date"));
                            eventObj.setStart_time(attribute.getString("start_time"));
                            eventObj.setEnd_time(attribute.getString("end_time"));
                            eventObj.setLocation(attribute.getString("location"));
                            eventObj.setPicture_path(attribute.getString("picture_path"));
                            eventObj.setSmall_picture_path(attribute.getString("small_picture_path"));

                            eventList.add(eventObj);
//                          DatabaseUser.openWritable();
//                          DatabaseUser.insertEvent(eventObj);
                            eventObj = null;
                        }
                    }
                    catch (JSONException e)
                    {
                        e.printStackTrace();
                        error = true;
                    }
                }
                else
                {
                    error = true;
                }


            } 
            catch (ClientProtocolException e) 
            {
                // process execption
                error = true;
            } 
            catch (IOException e)
            {
                // process execption
                error = true;
            }
            return error;
        }
}

大多数情况下，应用程序会在从onStart到onDestroy之后停止检索3次。