如何使用片段保留活动之间的动态Arraylist元素（Android）

Question

When one activity in the fragment is launched, it successfully requests POST method ( with AsyncTask ) and Arraylist is populated.

After I move to other activity in the fragment and comeback, what previously was populated seems gone, but when I click back button, then suddenly it populates again ( I'm not sure whether it is being populated or just hidden data shows up ). But again if I do the same work ( switching to other activity and come back ), then what previously was populated is gone and never come back.

I assume if it were to start from the first line of the code when I came back, then it should've populated but I think it didn't. But I really want to make an easier interface for the users by setting the populated data always visible.

Below is my code for "that" activity and also I include the code for the fragment controller.

public class VideoCallFragment extends Fragment implements LifeCycleListener{
    private LinearLayout parentFragment;
    private ViewGroup.LayoutParams selfLayoutParams;
    private ArrayList<String> prgmNameList = new ArrayList<String>();
    private ArrayList<String> caseList = new ArrayList<String>();
    private ArrayList<String> dateList = new ArrayList<String>();

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.fragment_video_call, container, false);
        parentFragment = (LinearLayout) rootView.findViewById(R.id.ll_video_call);

        SharedPreferences settings = PreferenceManager
                .getDefaultSharedPreferences(getContext());
        String auth_token_string = settings.getString("token", ""/*default value*/);

        new soonClass().execute(auth_token_string);

        final ListView lv=(ListView) rootView.findViewById(R.id.listView_classroom);
        lv.setAdapter(new CustomAdapter(getActivity(), prgmNameList, dateList, caseList));

        lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                    String classroom = ((TextView) view.findViewById(R.id.lesson)).getText().toString();
                    lv.setVisibility(View.GONE);
                    Toast.makeText(getActivity(),classroom,Toast.LENGTH_SHORT).show();
                    classroom_enter(classroom);
                }
            }
        );
        return rootView;
    }

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

        private Exception exception;
        protected void onPreExecute() {
        }

        protected String doInBackground(String... args) {
            String auth_token_string = args[0];

            try {
                URL url = new URL("myurl");
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();

                String urlParameters = "token=" + auth_token_string ;

                connection.setRequestMethod("POST");
                connection.setDoOutput(true);
                DataOutputStream dStream = new DataOutputStream(connection.getOutputStream());

                dStream.writeBytes(urlParameters);
                dStream.flush();
                dStream.close();

                InputStream in = connection.getInputStream();

                BufferedReader reader = new BufferedReader(new InputStreamReader(in,"iso-8859-1"),8);
                StringBuffer buffer = new StringBuffer();

                String line = "";
                while ((line = reader.readLine()) != null) {
                    buffer.append(line).append("\n");
                }
                reader.close();
                connection.disconnect();
                JSONObject jsonObj = null;

                jsonObj = new JSONObject(buffer.toString().trim());

                JSONArray classes = null;
                classes = jsonObj.getJSONArray("lessons");

                // looping through All Contacts
                for (int i = 0; i < classes.length(); i++) {
                    JSONObject c = classes.getJSONObject(i);

                    prgmNameList.add("lesson_" + c.getString("id"));
                    caseList.add(c.getString("course"));
                    dateList.add(c.getString("date"));
                }

                return "done";
            }
            catch(Exception e) {
                Log.e("ERROR", e.getMessage(), e);
                return null;
            }
        }

        protected void onPostExecute(String response) {
            Toast.makeText(getActivity(), "된다", Toast.LENGTH_SHORT).show();

            if(response == null) {
                response = "THERE WAS AN ERROR";
            }
            //progressBar.setVisibility(View.GONE);
            Log.i("INFO", response);
            //responseView.setText(response);
        }
    }

    public void classroom_enter(String room_name) {

        somefunction();
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Allow volume to be controlled using volume keys
        getActivity().setVolumeControlStream(AudioManager.STREAM_VOICE_CALL);
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        ((MainActivity2) activity).onSectionAttached(
                getArguments().getInt(ARG_SECTION_NUMBER));
    }

    @Override
    public void onDetach() {
        super.onDetach();
    }
}

fragment activity code

public class MainActivity2 extends ActionBarActivity
        implements NavigationDrawerFragment.NavigationDrawerCallbacks {
    private static final int CASE_SECTION_EDIT_PROFILE = 1;
    private static final int CASE_SECTION_VIDEO_CALL = 2;
    private static final int CASE_SECTION_PAST_CLASS = 3;
    private static final int CASE_SECTION_SCHEDULE_CLASS = 4;
    private static final int CASE_FRAGMENT_EDIT_PROFILE = 0;
    private static final int CASE_FRAGMENT_VIDEO_CALL = 1;
    private static final int CASE_FRAGMENT_PAST_CLASS = 2;
    private static final int CASE_FRAGMENT_SCHEDULE_CLASS = 3;
    private static final String TAG = MainActivity2.class.getName();

    private NavigationDrawerFragment mNavigationDrawerFragment;
    private CharSequence mTitle;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.mainactivity2);

        mNavigationDrawerFragment = (NavigationDrawerFragment)
                getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
        mTitle = getTitle();

        mNavigationDrawerFragment.setUp(
                R.id.navigation_drawer,
                (DrawerLayout) findViewById(R.id.drawer_layout));
    }

    @Override
    public void onNavigationDrawerItemSelected(int position) {
        // update the main content by replacing fragments
        FragmentManager fragmentManager = getSupportFragmentManager();

        Fragment fragmentToLaunch = getFragmentToLaunch(position);

        fragmentManager.beginTransaction()
                .replace(R.id.container, fragmentToLaunch)
                .commit();
    }

    public void onSectionAttached(int number) {
        switch (number) {
            case CASE_SECTION_EDIT_PROFILE:
                mTitle = getString(R.string.title_section1);
                break;
            case CASE_SECTION_VIDEO_CALL:
                mTitle = getString(R.string.title_section2);
                break;
            case CASE_SECTION_PAST_CLASS:
                mTitle = getString(R.string.title_section3);
                break;
            case CASE_SECTION_SCHEDULE_CLASS:
                mTitle = getString(R.string.title_section4);
                break;
            default:
                break;
        }
    }

    public void restoreActionBar() {
        ActionBar actionBar = getSupportActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
        actionBar.setDisplayShowTitleEnabled(true);
        actionBar.setTitle(mTitle);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        if (!mNavigationDrawerFragment.isDrawerOpen()) {
            // Only show items in the action bar relevant to this screen
            // if the drawer is not showing. Otherwise, let the drawer
            // decide what to show in the action bar.
            getMenuInflater().inflate(R.menu.main, menu);
            restoreActionBar();
            return true;
        }
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        return super.onOptionsItemSelected(item);
    }

    public Fragment getFragmentToLaunch(int position) {
        Fragment fragmentToLaunch = null;
        switch (position) {
            case CASE_FRAGMENT_EDIT_PROFILE:
                fragmentToLaunch = new EditProfileFragment();  // <!-- this is a class.
                break;
            case CASE_FRAGMENT_VIDEO_CALL:
                fragmentToLaunch = new VideoCallFragment();
                break;
            case CASE_FRAGMENT_PAST_CLASS:
                fragmentToLaunch = new ChatFragment();
                break;
            case CASE_FRAGMENT_SCHEDULE_CLASS:
                fragmentToLaunch = new FileTransferFragment();
                break;
            default:
                break;
        }

        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, position + 1);
        fragmentToLaunch.setArguments(args);

        return fragmentToLaunch;
    }
}

please give me any opinion about how to solve this issue!!! (:

Answer 1

Call Asynctask in your fragment (VideoCallFragment) onResume() method

@Override
public void onResume() {
    super.onResume();
    new soonClass().execute(auth_token_string);
}