How to save List in onDestroyView in Fragment?

Question

I am trying to implement Instagram-like user profile screen. This is my flow ProfileFragment --> SingleImageFragment --> ProfileFragment --> SingleImageFragment. So, the user can have multiple instances of the same fragment. I don't want to hide/show because it costs too much memory. So I am using

mFragment = fragment;
    mFragmentManager
            .beginTransaction()
            .replace(R.id.frame_container, fragment, Integer.toString(getFragmentCount()))
            .addToBackStack(null)
            .commit();

But, this way ProfileFragment goes into onDestroyView and when it is returned from backStack the list will be loaded again since it goes to onViewCreated method. I am trying to find a way how to not load the data that has already been loaded when coming to that fragment. Is there a way that I can save the already loaded list and use that one in onViewCreated?

This is ProfileFragment:

    public class ProfileFragment extends BaseChildFragment implements ProfileAdapter.OnHeaderItemClickedListener,
        SwipeRefreshLayout.OnRefreshListener {

    public static final String ACTION_SINGLE_IMAGE = ProfileFragment.class.getName() + ".single_image";
    public static final String ACTION_SETTINGS = ProfileFragment.class.getName() + ".settings";
    private static final String ARG_PARAM1 = "param1";

    FragmentProfileBinding mBinder;
    FragmentManager mFragmentManager;
    Home mHome;
    Home tHome;
    List<Home> mHomeList;
    ProfileAdapter mAdapter;
    StaggeredGridLayoutManager mManager;
    EndlessRecyclerViewScrollListener mEndlessScrollListener;
    PreferenceAdapter mPreferenceAdapter;
    int mInstance;

    public ProfileFragment() {

    }

    public static ProfileFragment newInstance(int instance) {
        ProfileFragment fragment = new ProfileFragment();
        Bundle args = new Bundle();
        args.putInt(ARGS_INSTANCE, instance);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mInstance = getArguments().getInt(ARGS_INSTANCE);
        }
        mHomeList = new ArrayList<>();
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        mBinder = DataBindingUtil.inflate(inflater, R.layout.fragment_profile, container, false);
        mFragmentManager = getChildFragmentManager();
        mHome = new Home();
        tHome = new Home();
        mPreferenceAdapter = new PreferenceAdapter(getContext());
        mManager = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL);
        mAdapter = new ProfileAdapter(getContext(), mHomeList);
        mBinder.rvGrid.setLayoutManager(mManager);
        mBinder.rvGrid.setAdapter(mAdapter);
        mAdapter.addOnHeaderItemClickListener(this);
        mBinder.srLayout.setOnRefreshListener(this);
        mEndlessScrollListener = new EndlessRecyclerViewScrollListener(mManager) {
            @Override
            public void onLoadMore(int page, int totalItemsCount, RecyclerView view) {
                populateList();
                populateSecondList();
                mAdapter.notifyDataSetChanged();
            }
        };
        mBinder.rvGrid.addOnScrollListener(mEndlessScrollListener);
        setUIListeners();
        return mBinder.getRoot();
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        populateList();
        populateSecondList();
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        mAdapter.removeOnHeaderItemClickListener();
        mBinder.rvGrid.removeOnScrollListener(mEndlessScrollListener);
    }

    private void setUIListeners() {
    }

    @Override
    public void onGridImageClicked(Home home) {
        sendActionToParent(ACTION_SINGLE_IMAGE);
    }

    @Override
    public void onRefresh() {
        mHomeList.clear();
        populateList();
        populateSecondList();
        mAdapter.notifyDataSetChanged();
        mEndlessScrollListener.resetState();
        mBinder.srLayout.setRefreshing(false);
    }

    private void sendActionToParent(String action) {
        if (mParentListener == null) {
            return;
        }
        Bundle bundle = new Bundle();
        bundle.putString(Constants.ACTION_KEY, action);
        mParentListener.onChildFragmentInteraction(bundle);
    }

    private void sendActionToActivity(String action) {
        if (mActivityListener == null) {
            return;
        }
        Bundle bundle = new Bundle();
        bundle.putString(Constants.ACTION_KEY, action);
        mActivityListener.onChildFragmentToActivityInteraction(bundle);
    }

    private void populateList() {
        for (int i = 0; i < 5; i++) {
            mHome.setType(0);
            mHomeList.add(i, mHome);
        }
    }

    private void populateSecondList() {
        for (int i = 0; i < 5; i++) {
            tHome.setType(1);
            mHomeList.add(i, tHome);
        }
    }
}

score 0 · Answer 1 · answered Apr 25 '17 at 12:02

Yes, you can try to use setRetainInstance(true); (add this line in your onCreate() method) to retain the state of your Fragment.

Or you can try to use SQLite or an ORM Framework to persist the list into a database. I advise you to use ORMLite to save your list:

To use ORMLite in your project, add this line in your gradle.build file (module:app)

compile group: 'com.j256.ormlite', name: 'ormlite-android', version: '4.45'

And then, you have to create a wrapper class and put your list inside it:

@DatabaseTable(tableName = "your_table_name")
public class YourClass{

@DatabaseField(generatedId = true)
private int id;

@DatabaseField(dataType = DataType.SERIALIZABLE)
private List<YourList> list;

//getters and setters here

}

Now, you have to create your DatabaseHelper:

public class DatabaseHelper extends OrmLiteSqliteOpenHelper {

    // name of the database file for your application -- change to something appropriate for your app
    private static final String DATABASE_NAME = "yourdatabasename.db";
    // any time you make changes to your database objects, you may have to increase the database version
    private static final int DATABASE_VERSION = 1;

    // the DAO object we use to access the SimpleData table
    private Dao<YourClass, Integer> simpleDao = null;
    private RuntimeExceptionDao<YourClass, Integer> simpleRuntimeDao = null;

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION, R.raw.ormlite_config);
    }

    /**
     * This is called when the database is first created. Usually you should call createTable statements here to create
     * the tables that will store your data.
     */
    @Override
    public void onCreate(SQLiteDatabase db, ConnectionSource connectionSource) {
        try {
            Log.i(DatabaseHelper.class.getName(), "onCreate");
            TableUtils.createTable(connectionSource, SimpleData.class);
        } catch (SQLException e) {
            Log.e(DatabaseHelper.class.getName(), "Can't create database", e);
            throw new RuntimeException(e);
        }

        // here we try inserting data in the on-create as a test
        RuntimeExceptionDao<YourClass, Integer> dao = getSimpleDataDao();
        long millis = System.currentTimeMillis();
        // create some entries in the onCreate
        YourClass simple = new YourClass();
        dao.create(simple);
        simple = new YourClass();
        dao.create(simple);
        Log.i(DatabaseHelper.class.getName(), "created new entries in onCreate: " + millis);
    }

    /**
     * This is called when your application is upgraded and it has a higher version number. This allows you to adjust
     * the various data to match the new version number.
     */
    @Override
    public void onUpgrade(SQLiteDatabase db, ConnectionSource connectionSource, int oldVersion, int newVersion) {
        try {
            Log.i(DatabaseHelper.class.getName(), "onUpgrade");
            TableUtils.dropTable(connectionSource, SimpleData.class, true);
            // after we drop the old databases, we create the new ones
            onCreate(db, connectionSource);
        } catch (SQLException e) {
            Log.e(DatabaseHelper.class.getName(), "Can't drop databases", e);
            throw new RuntimeException(e);
        }
    }

    /**
     * Returns the Database Access Object (DAO) for our SimpleData class. It will create it or just give the cached
     * value.
     */
    public Dao<YourClass, Integer> getDao() throws SQLException {
        if (simpleDao == null) {
            simpleDao = getDao(SimpleData.class);
        }
        return simpleDao;
    }

    /**
     * Returns the RuntimeExceptionDao (Database Access Object) version of a Dao for our SimpleData class. It will
     * create it or just give the cached value. RuntimeExceptionDao only through RuntimeExceptions.
     */
    public RuntimeExceptionDao<SimpleData, Integer> getSimpleDataDao() {
        if (simpleRuntimeDao == null) {
            simpleRuntimeDao = getRuntimeExceptionDao(SimpleData.class);
        }
        return simpleRuntimeDao;
    }

    /**
     * Close the database connections and clear any cached DAOs.
     */
    @Override
    public void close() {
        super.close();
        simpleDao = null;
        simpleRuntimeDao = null;
    }

And finally, save your list and recover it when you want:

//To query all:
Yourclass class = simpleDao.queryForAll();

//To save data:
simpleDao.create(your_object_whit_lists);

With `setRetainInstance(true)` the lifecycle goes to `onDestroyView` when I go to another fragment. When I come back to it, from `backStack`, it goes into `onViewCreated` again, so my list is never saved. — Esteban, Apr 25 '17 at 12:09
in this case, you have to use the 2 option, use a SQLite or ORMLite — Luiz Fernando Salvaterra, Apr 25 '17 at 12:12
Hmm but then I would have to store separate lists for each fragment and delete them when the fragment is destroyed. Because I might have 4 instances of `ProfileFragment`, each of them with different list. — Esteban, Apr 25 '17 at 12:32

score 0 · Answer 2 · edited May 23 '17 at 12:26

Use savedInstanceState for the example

Make your 'Home' pojo class implement Parcelable.
Change List mHomeList to ArrayList mHomeList.

Implement onSaveInstanceState(Bundle outState) on your fragment and put mHomeList to sate bundle.

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putParcelableArrayList("STATE_HOME_LIST", mHomeList);
}

In onViewCreated() you can restore your mHomeList like this

if (savedInstanceState != null) {
    mHomeList = savedInstanceState.getParcelableArrayList("STATE_HOME_LIST");
    //  do something // update Adapter
}else {
    populateList();
    populateSecondList();
}

By replacing the fragments in the same activity, the fragment never calls `onSaveInstanceState`. I need to save the list as `parcelable` but where do I save it if `onSaveInstanceState` is never called? — Esteban, Apr 25 '17 at 12:31

score 0 · Accepted Answer · edited May 23 '17 at 11:33

Based on the second answer of this question, I've come up with this solution. I don't know how reliable it's going to be though.

I save the list in Bundle:

private Bundle saveState() {
    Bundle state = new Bundle();
    Parcelable parcelable = Parcels.wrap(mHomeList);
    state.putParcelable("homeList", parcelable);
    return state;
}

And then in onViewCreated:

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    if (savedState != null) {
        mHomeList = Parcels.unwrap(savedState.getParcelable("homeList"));
    } else {
        populateList();
        populateSecondList();
    }
    savedState = null;
    Log.d("TAG", "PROFILE: " + mHomeList.size());
}

How to save List in onDestroyView in Fragment?

3 Answers3