Implementing Fragment instantiation causes opposite effect

Question

I have implemented my fragment to the Android's best practice of using newInstance with parameters. It works, but with a hatch.

The issue the newInstance with parameters fixes is that Android will call the default no-args constructor on screen rotation. That means you will lose data on rotation. The newInstance will allow you to setArguments that will be retained on rotation.

Using the overloaded constructor will mean your data will show correctly the first time until you rotate your device. The newInstance will allow your fragment to work correctly the first time and on rotations.

Issues

However, it seems like I am having the opposite effect. My code works correctly on rotations, but does not work correctly on the first try. The same effect occurs if I use the constructor with arguments.

On app load, it will display my tabs (3) in a Tablayout but none of my RecyclerViews will have items in them.

Here is how I can load data into the RecyclerViews the fastest. All on app load, and all are from fresh starts:

1. Rotate the device. All 3 tabs will load their data. Current tab right now, and other tabs on selection (sliding to them).
2. From 1st Tab, click on Tab 3, then go back to Tab 1. Tab 1 data will load. Tab 2 won't load. Tab 3 will load on selection. To get Tab 2 data to load, I need to rotate the device

Code

Fragment

public class MovieListFragment extends Fragment implements OnItemClickListener {

    MovieListAdapter adapter;
    WebAPI webAPI;     // Advanced Enum

    private static final String API_STRING = "api";

    public MovieListFragment() {}

    public static MovieListFragment newInstance(WebAPI API) {

        MovieListFragment fragment = new MovieListFragment();

        Bundle args = new Bundle();
        args.putSerializable(API_STRING, API);
        fragment.setArguments(args);

//        if (API != null) fragment.webAPI = API;

        return fragment;

    }

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

        View rootView = inflater.inflate(R.layout.fragment_movies_list, container, false);

        webAPI = (WebAPI) getArguments().getSerializable(API_STRING);

        GetMoviesAsync getMovies = new GetMoviesAsync();
        getMovies.execute();

        adapter = new MovieListAdapter(getActivity(), webAPI, this);

        RecyclerView movieListView;

        movieListView = (RecyclerView) rootView.findViewById(R.id.movie_list);
        movieListView.setAdapter(adapter);
        movieListView.setLayoutManager(
                new GridLayoutManager(  // Changes number of columns based on form-factor and orientation
                        getActivity(),
                        getResources().getInteger(R.integer.columns)));


        return rootView;

    }

    @Override
    public void onClick(View v, int position) {

        startActivity(new Intent(this.getActivity(), SecondaryActivity.class)); // TODO pass data to second activity

    }

    // ASYNC_TASK
    public class GetMoviesAsync extends AsyncTask<Void, Void, Void> {

        // CALLBACK
        private final Handler.Callback getMoviesFromJSON = new Handler.Callback() {

            @Override
            public boolean handleMessage(Message msg) {

                        // Take the JSON (msg) and convert it to a Java object (Movie)
                        Movie movie = new Movie(title, uri);
                        webAPI.addMovie(movie);

                    }

                } catch (JSONException e) { return false; }

                return true;

            }

        };

        @Override
        protected Void doInBackground(Void... params) {

            try {

                // This will get the JSON from the webservice, and will use the CallBack to assign the List of movies.
                new WebService(webAPI.getUri()).acquireDataWithCallback(getMoviesFromJSON);

            } catch (JSONException e) { e.printStackTrace(); }

            return null;
        }

    }

}

BaseActivity

public abstract class BaseSearchTabbedActivity extends AppCompatActivity
        implements SearchView.OnQueryTextListener {

    EnumSet<WebAPI> tabs;
    ...

    public void setTabs(EnumSet<WebAPI> tabs) { this.tabs = tabs; }

    void initializeToolbar() {   // Called in Activity's OnCreate

        // Setup the toolbar
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        // Initialize all components. Tabs, Pager, and Adapter
        tabLayout = (TabLayout) findViewById(R.id.tabs);
        viewPager = (ViewPager) findViewById(R.id.pager);
        adapter = new ViewPagerFragmentAdapter(getSupportFragmentManager());

        // Add the tabs
        collectTabValues(); // Set tabs from Activity
        addFragments(tabs);

        // Bind the adapter to the tabs
        viewPager.setAdapter(adapter);
        tabLayout.setupWithViewPager(viewPager);

    }

    private void addFragments(EnumSet<WebAPI> tabs) {

        for (WebAPI tab : tabs) {

            adapter.addFragment(MovieListFragment.newInstance(tab), tab);

        }

    }

Answer 1

Whenever the async task completes its work, you would need to update the adapter and notify its items there were changes.

Updating adapter views needs to be in the main thread, so please add the following method in your task:

@Override
protected void onPostExecute(Void nothing) {
    adapter.notifyDataSetChanged();
}