如何使用片段保留活動之間的動態Arraylist元素（Android）

Question

啟動片段中的一個活動時，它將成功請求POST方法（帶有AsyncTask ），並填充Arraylist 。

當我移到片段中的其他活動並恢復時，以前填充的內容似乎消失了，但是當我單擊“后退”按鈕時，突然又填充了它（我不確定是要填充它還是只是顯示隱藏的數據）。 但是同樣，如果我做同樣的工作（切換到其他活動然后再回來），那么以前填充的內容就消失了，再也不會回來。

我假設如果它是從我回來時從代碼的第一行開始的，那么它應該已經填充了，但我認為沒有。 但是我真的想通過將填充的數據設置為始終可見來為用戶提供一個更簡單的界面。

以下是我的“ that”活動代碼，還包括片段控制器的代碼。

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();
    }
}

片段活動代碼

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;
    }
}

請給我有關如何解決此問題的任何意見！！！ （：

Answer 1

在片段（VideoCallFragment） onResume（）方法中調用Asynctask

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