RecyclerView not showing anything after updating Adapter data

Question

guys i need help with this matter i have been going through my code for a couple of days to figure whats going wrong but i couldn't figure it out. I have a fragment with a RecyclerView i initialize the Adapter data with an image place holder and some default text and the fragment shows them as expected then using a loader i fetch data from the internet and parse and pass the new data to the Adapter (all of this happens as required) until the data reaches the Adapter then Taaadaaaa the initial data disappears and the new data is not showing actually the fragment shows a blank screen definitely i am doing something wrong please advise. This is the fragment code

public class fragment_MovieStartGridlayout extends android.support.v4.app.Fragment implements MyGridAdapter.MyGridAdapterListener{

private static RecyclerView myRecyclerView;
private static MyGridAdapter myGridAdapter;
private static RecyclerView.LayoutManager rvLayoutManager;
private LoaderManager.LoaderCallbacks<ArrayList<HashMap>> dataLoaderCallbacks;


private OnFragmentInteractionListener mListener;

public fragment_MovieStartGridlayout() {

}

@Override
public void onActivityCreated  (Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

  dataLoaderCallbacks = new LoaderManager.LoaderCallbacks<ArrayList<HashMap>>() {

  @Override
  public Loader<ArrayList<HashMap>> onCreateLoader(int id, Bundle args) {
   return new DataLoader(getActivityContext(), MyUriBuilder.DISCOVER, null);
            }

@Override
public void onLoadFinished(Loader<ArrayList<HashMap>> loader,ArrayList<HashMap> data) {
                myGridAdapter.setMyAdapterData(data);
            }

            @Override
            public void onLoaderReset(Loader<ArrayList<HashMap>> loader) {
                loader.reset();
            }

        };
        getLoaderManager().initLoader(0, null, dataLoaderCallbacks);

    setRetainInstance(true);
}

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

    View fragGridLayout = inflater.inflate(R.layout.fragment_gridlayout_movie_start, container, false);
    myRecyclerView = (RecyclerView) fragGridLayout.findViewById(R.id.myViewRecycler);
    rvLayoutManager = new GridLayoutManager(getActivityContext(),2);
    myRecyclerView.setLayoutManager(rvLayoutManager);
    myGridAdapter = new MyGridAdapter(getActivityContext());
    myRecyclerView.setAdapter(myGridAdapter);

    return fragGridLayout;
}


@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    try {
        mListener = (OnFragmentInteractionListener) activity;
    } catch (ClassCastException e) {
        throw new ClassCastException(activity.toString()
                + " must implement OnFragmentInteractionListener");
    }
}

@Override
public void onDataSetChanged(boolean state) {
    if (state){
        myGridAdapter.notifyDataSetChanged();
    }
}


public interface OnFragmentInteractionListener {
    public void onFragmentInteraction(Uri uri);
}


    public Context getActivityContext(){
        return this.getActivity();
    }

}

and this is the Adapter for the RecyclerView

 public class MyGridAdapter extends RecyclerView.Adapter<MyGridAdapter.MyViewHolder> {

LayoutInflater layoutInflater;
private static ArrayList<HashMap> data=null;
private Context mContext;
public static Bitmap placeHolder;
    public MyGridAdapter(Context context){
      mContext = context;
      setInitialData();
      placeHolder =    BitmapFactory.decodeResource(mContext.getResources(),R.drawable.android_blue);
}
    public interface MyGridAdapterListener{
        public void onDataSetChanged(boolean state);
    }

private MyGridAdapterListener listener = null;
public void registerListener(MyGridAdapterListener newListener){
    listener = newListener;
}

@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    Context context = parent.getContext();
    layoutInflater = LayoutInflater.from(context);
    View v = layoutInflater.inflate(R.layout.gridlayout_item_movie_start, parent, false);
    MyViewHolder vHolder=new MyViewHolder(v);
    return vHolder;
}

@Override
public void onBindViewHolder(MyViewHolder holder, int position) {

      HashMap singleData = data.get(position);
      String movieRate = String.valueOf(singleData.get(MyJSONDataParser.TAG_VOTE_AVERAGE)) ;
        holder.movieTitle.setText((String)singleData.get(MyJSONDataParser.TAG_TITLE));
        holder.moviePoster.setImageBitmap(placeHolder);
        holder.movieRating.setRating(Float.valueOf(movieRate));
}

@Override
public int getItemCount() {
    return data.size();
}


public static class MyViewHolder extends RecyclerView.ViewHolder  {
    TextView movieTitle;
    RoundedImageView moviePoster;
    RatingBar movieRating;

    public MyViewHolder(View v) {
        super(v);
        movieTitle = (TextView) v.findViewById(R.id.movieTitleTextView);
        moviePoster = (RoundedImageView) v.findViewById(R.id.roundImageView);
        movieRating = (RatingBar) v.findViewById(R.id.ratingBar);
    }
}


private boolean dataChanged = false;

public void setMyAdapterData(ArrayList<HashMap> data){
        this.data = data;
        dataChanged = true;
        if (listener != null){
            listener.onDataSetChanged(dataChanged);
        }
    }


protected void setInitialData(){
    HashMap initialItem = new HashMap();
    ArrayList<HashMap> initialData = new ArrayList<>(20);

    initialItem.put(MyJSONDataParser.TAG_TITLE, "Loading...");
    initialItem.put(MyJSONDataParser.TAG_MOVIE_BITMAP, placeHolder);
    initialItem.put(MyJSONDataParser.TAG_VOTE_AVERAGE, 3.3);
    for (int i = 0;i<20;i++){
        initialData.add(initialItem);
    }
    this.data = initialData;
}

}

Answer 1

I did call notifyDataSetChanged but this was not the issue after alooooooooot of testing and Logging the problem was with setAdapterData method where i just passed the data reference from the loader to the adapter but this didn't work and i had to clone the arraylist instead of just passing the reference which sounds strange to me and i still don't understand why I had to do that if you can take a look at the setAdapterData method in MyGridAdapter class and tell me what do you think

Answer 2

Try invoking notifyDataSetChanged() when you modify your adapter data:

public void setMyAdapterData(ArrayList<HashMap> data){
    this.data = data;
    dataChanged = true;
    notifyDataSetChanged();
    if (listener != null){
        listener.onDataSetChanged(dataChanged);
    }
}

I see that you attempt to do this in the callback on your listener, but perhaps it is null and therefore never firing the notification?

[COMMENT] When I want to replace the entire collection of data in my adapter I often write a method similar to this:

public void setData(List<MyData> newData) {
    this.data.clear();
    this.data.addAll(newData);
    this.notifyDataSetChanged();
}