Data is getting added into list instead of getting updated in addChildEventListener's onChildChanged()

Question

I have some data in firebase which gets changed on some specific actions and I want that change to be shown in the app.

I have a RecyclerView in which all the data from firebase is getting populated.

Here's code:

    databaseReference.child("uListings").child(AccessToken.getCurrentAccessToken().getUserId()).addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                // recyclerview gets populated here
            }

            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String s) {
                if (dataSnapshot.getValue() != null) {
                    Map<String,String> map = (Map<String,String>)dataSnapshot.getValue();
                    Map<ArrayList<String>,ArrayList<String>> map2 = (Map<ArrayList<String>,ArrayList<String>>)dataSnapshot.getValue();
                    String pDescription = map.get("pDescription");
                    String pDuration = map.get("pDuration");
                    String pPrice = map.get("pPrice");
                    String postedAt = map.get("postedAt");
                    String views = map.get("views");
                    ArrayList<String> imageUrl = map2.get("imageUrl");

                            if (imageUrl != null) {
                                UHandler pHandler = new UHandler(imageUrl.get(0), pDescription, pDuration, pPrice, postedAt, views);
                                list.add(pHandler);
                                adapter.notifyDataSetChanged();
                                progressBar.setVisibility(View.INVISIBLE);
                            } else {
                                Toast.makeText(getBaseContext(), "imageUrlNone", Toast.LENGTH_SHORT).show();
                            }

                } else {
                    Log.d("PDPchange", "NULL");
                    progressBar.setVisibility(View.INVISIBLE);
                }
            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {

            }

            @Override
            public void onChildMoved(DataSnapshot dataSnapshot, String s) {

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

Here's UHandlerAdapter.java:

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

    private Context mContext;
    private List<UHandler> listingList;

    public class MyViewHolder extends RecyclerView.ViewHolder {
        public TextView pDescription, pDuration, pPrice, postedAt, listingViews, imageUrl;
        public ArrayList<String> imageUrls;
        public CircleImageView pImage;


        public MyViewHolder(View view) {
            super(view);
            pImage = (CircleImageView) view.findViewById(R.id.p_image_profile);
            pDescription = (TextView) view.findViewById(R.id.p_description_profile);
            pDuration = (TextView) view.findViewById(R.id.p_duration_profile);
            pPrice = (TextView) view.findViewById(R.id.p_price_profile);
            postedAt = (TextView) view.findViewById(R.id.p_posted_when_profile);
            listingViews = (TextView) view.findViewById(R.id.listing_views_profile);
            imageUrl = (TextView) view.findViewById(R.id.image_urls_profile);
        }
    }


    public UHandlerAdapter(Context mContext, List<UProfileHandler> listingList) {
        this.mContext = mContext;
        this.listingList = listingList;
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.profile_all, parent, false);

        return new MyViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(final MyViewHolder holder, int position) {
        UHandler handler = listingList.get(position);
        holder.pDescription.setText(handler.getPDescriptionProfile());
        holder.pDuration.setText(handler.getPDurationProfile());
        holder.pPrice.setText(handler.getPPriceProfile());
        holder.postedAt.setText(handler.getPostedAt());
        holder.listingViews.setText(handler.getListingViews());

        // loading album cover using Glide library
        Glide.with(mContext)
                .load(handler.getPImageProfile())
                .apply(new RequestOptions().placeholder(R.drawable.ic_placeholder).error(R.drawable.ic_error))
                .into(holder.pImage);

    }

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

The problem is that in onChildChanged() the views which gets changed add a complete other item in the list reflecting it's changed value and not just gets updated in previously added items in onChildAdded().

How can I just update it in the previously added items itself?

First of all you have a bug with `ArrayList imageUrl = map2.get("imageUrl");` `map.get(Object key)` is not type safe ie. the compiler wont complain if you give a key of the wrong type. See https://stackoverflow.com/questions/857420/what-are-the-reasons-why-map-getobject-key-is-not-fully-generic for further info. — alan7678, Oct 12 '17 at 16:11
@alan7678 okay. Thanks for pointing it out. Please also answer the question asked. — Hammad Nasir, Oct 12 '17 at 16:24
Assuming `UHandler` is your view model, you should not be using `new` if you don't want a new item. So to put it simply do not use `new` do not use `list.add`, use `list.get` to retrieve your object and update it. — alan7678, Oct 12 '17 at 16:35
@alan7678 how can I retrieve object with list.get here. There is no way to know the position here because the data can get updated for any item in the list. — Hammad Nasir, Oct 12 '17 at 18:41
You mean there is new data added into the adapter or to the firebase ? if first choice, you may have to provide your adapter here. — , Oct 14 '17 at 16:43
@HammadNasir so why you are using different lists int he adapter `UProfileHandler` and `UHandler`? It's better to be the same `model` — , Oct 14 '17 at 18:47
@HammadNasir one easy solution is to `reload` or `refresh` the layout. — , Oct 14 '17 at 19:07
@Ibrahim hmm.. but it'd affect the user experience... I tried looping through but got a `nullpointerexception`. — Hammad Nasir, Oct 14 '17 at 19:11

score 2 · Accepted Answer · answered Oct 14 '17 at 19:18

You can store keys in order to update it e.g:

 ArrayList<String> mKeys = new ArrayList<String>();  

databaseReference.child("uListings").child(AccessToken.getCurrentAccessToken().getUserId()).addChildEventListener(new ChildEventListener() {
                    @Override
                    public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                        // recyclerview gets populated here

                        String key = dataSnapshot.getKey();
                        mKeys.add(key);
                        adapter.notifyDataSetChanged();

                    }

                    @Override
                    public void onChildChanged(DataSnapshot dataSnapshot, String s) {
                        if (dataSnapshot.getValue() != null) {
                             .......
                             //now we get the index to update specific value
                              String key = dataSnapshot.getKey();
                              int index = mKeys.indexOf(key);
                              list.set(index, pHandler);

                              adapter.notifyDataSetChanged();
                              ....
                    }

This worked! Will award the bounty after 14 hours (as prompted by StackOverflow). — Hammad Nasir, Oct 14 '17 at 19:55
hmm.. well I think it needs just a logic instead of any feature from library. Can you please take a good look on the question? — Hammad Nasir, Oct 14 '17 at 20:31
salaam. please take a look at this one: https://stackoverflow.com/questions/46761756/if-statement-not-returning-the-correct-elements-on-retrieving-data-from-firebase — Hammad Nasir, Oct 17 '17 at 19:29

Data is getting added into list instead of getting updated in addChildEventListener's onChildChanged()

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