RecyclerView .add() is working without calling .notifyDataSetChanged() after initializing adapter

Question

In my adapter why is .add() working even though I already set the adapter?

mFilePathImages = new ArrayList<>();
mGridAdapter = new HomeGridAdapter(mContext, mFilePathImages);    
mGridRecycler.setLayoutManager(gridLayoutManager);
mGridRecycler.setAdapter(mGridAdapter);

mFilePathImages.add("https://i.redd.it/lawrnev8v8o41.jpg");
mFilePathImages.add("https://i.imgur.com/GQXyo34.jpg");

Shouldn't it only work if I called .notifyDataSetChanged?

I checked my adapter to see if there was .notifyDataSetChanged, but there wasn't.

Here is the the full adapter for the Recycler:

public class HomeGridAdapter extends RecyclerView.Adapter<HomeGridAdapter.ViewHolder> {

    private static final String TAG = "GridViewAdapter";

    private Context mContext;
    private ArrayList<String> mList;


    public HomeGridAdapter(Context context, ArrayList<String> list) {
        this.mContext = context;
        this.mList = list;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.vh_fraghome_griditem, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int i) {
        Glide.with(mContext)
                .load(mList.get(i))
                .apply(RequestOptions.centerCropTransform())
                .into(holder.vhSquareImage);
    }

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


    public class ViewHolder extends RecyclerView.ViewHolder {
        @BindView(R.id.vh_fraghome_squareimageview)
        SquareImageView vhSquareImage;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            ButterKnife.bind(this, itemView);
        }
    }
}
```

Anyone know whats causing the issue

@ShahoodulHassan I'm not even scrolling. I only added two items to test the adapter — Mike Litoris, Mar 23 '20 at 06:10

score 0 · Answer 1 · answered Mar 23 '20 at 06:15

0

I can assume that this is due to the fact that this code

mFilePathImages.add("https://i.redd.it/lawrnev8v8o41.jpg");
mFilePathImages.add("https://i.imgur.com/GQXyo34.jpg");

executes faster than the process of creating a view for recyclerView starts, so the call to notifyDataSetChanged is not required.Therefore, it works, but not the fact that it will work every time, so you should call notifyDataSetChanged

answered Mar 23 '20 at 06:15

Destroyer

785
8
20

Isn't the code executed top to bottom? Why would that be faster – Mike Litoris Mar 23 '20 at 06:16
No, onBindViewHolder is executed as needed, so you can manage to add list items before the drawing process starts. I can be wrong, but I think this is the only option. – Destroyer Mar 23 '20 at 06:18
You can use the debugger and test my theory. – Destroyer Mar 23 '20 at 06:20
I just tried with adding 100 images after initializing the adapter and it still works so I doubt this is the cause – Mike Litoris Mar 23 '20 at 06:21
Try to run the code to add elements in a new thread before setting a delay of 2 seconds and report the result – Destroyer Mar 23 '20 at 06:22

score -1 · Answer 2 · answered Mar 23 '20 at 06:39

Java is always pass-by-value. Unfortunately, when we pass the value of an object, we are passing the reference to it, as you did it here :

 new HomeGridAdapter(mContext, mFilePathImages);

so now, whenever you change your mFilePathImages array, it will also effects the adapter.

For better clarification see this answer : https://stackoverflow.com/a/12429953/9025616

for avoiding this situation you should pass array after you have final data(or any run-time changes). For adapter make list initially empty.

whenever you have your final data send it to your adapter as :

public void updateData(ArrayList<String> list) {
    if (list!= null) {
        this.list.clear();
        this.list.addAll(list);
        notifyDataSetChanged();
    }
}

RecyclerView .add() is working without calling .notifyDataSetChanged() after initializing adapter

2 Answers2