将滚动侦听器添加到RecyclerView适配器

Question

how to implement scroll listener to RecyclerView adapter so i can use on my activity class. You will find below my recycler view adapter. The reason i want scroll listener because i want the position to be changed when i scroll. right now it can only be changed if i click on the item inside the recycle view.

basically what i wanna do is i will have a text view in the activity class and when i scroll through the recyclerView i should get the name of item

 Activity activity;
    ArrayList<BookData> images = new ArrayList<>();
    AlbumDBHandler db;
    private Context mContext;

    public class MyViewHolder extends RecyclerView.ViewHolder {
        public ImageView thumbnail;
        public TextView name;
        public Button button;

        public MyViewHolder(View view) {
            super(view);

            thumbnail = (ImageView) view.findViewById(R.id.thumbnail);
            name = (TextView) view.findViewById(R.id.textViewGallery);
            button = (Button) view.findViewById(R.id.main_activity_button_carasoul);
        }
    }
    public GalleryAdapter(Context context, ArrayList<BookData> images) {
        mContext = context;
        this.images = images;
        this.db = new AlbumDBHandler(context);
    }
    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.gallery_thumbnail, parent, false);

        return new MyViewHolder(itemView);
    }
    @Override
    public void onBindViewHolder(final MyViewHolder holder, int position) {

        BookData image = images.get(position);

        if("".equals(images.get(position).getImageLocalPath())){

            Glide.with(mContext)
                    .load(images.get(position).getImagePath_2())
                    .thumbnail(0.5f)
                    .crossFade()
                    .diskCacheStrategy(DiskCacheStrategy.ALL)
                    .into(holder.thumbnail);

            new ImageDownloaderTask(images.get(position)).execute(images.get(position).getImagePath_2());

        }else{
            Glide.with(mContext).load(new File(images.get(position).getImageLocalPath())).into(holder.thumbnail);
        }

        holder.name.setText(images.get(position).getName());
        }

    class ImageDownloaderTask extends AsyncTask<String, Void, Bitmap> {
        private final WeakReference<BookData> bookDataWeakReference;

        public ImageDownloaderTask(BookData bookData) {
            bookDataWeakReference = new WeakReference<BookData>(bookData);
        }

        @Override
        protected Bitmap doInBackground(String... params) {
            return downloadBitmap(params[0]);
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            if (isCancelled()) {
                bitmap = null;
            }

            if (bookDataWeakReference != null && bitmap != null) {
                BookData bookData = bookDataWeakReference.get();
                if (bookData != null){

                    if (activity instanceof mainActivityCarasoul){
                        String path = FileUtils.saveBitmapToCamera(activity,bitmap,bookData.getName()+".jpg", BookData.Book).getPath();
                        bookData.setImageLocalPath(path);
                        db.updateABook(bookData);
                    }
                }
            }
        }
        private Bitmap downloadBitmap(String url) {
            HttpURLConnection urlConnection = null;
            try {
                URL uri = new URL(url);
                urlConnection = (HttpURLConnection) uri.openConnection();
                int statusCode = urlConnection.getResponseCode();
                if (statusCode != HttpURLConnection.HTTP_OK) {
                    return null;
                }

                InputStream inputStream = urlConnection.getInputStream();
                if (inputStream != null) {
                    Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                    return bitmap;
                }
            } catch (Exception e) {
                urlConnection.disconnect();
                Log.w("ImageDownloader", "Error downloading image from " + url);
            } finally {
                if (urlConnection != null) {
                    urlConnection.disconnect();
                }
            }
            return null;
        }
    }

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

    public interface ClickListener {
        void onClick(View view, int position);

        void onLongClick(View view, int position);
    }

    public static class RecyclerTouchListener implements RecyclerView.OnItemTouchListener {

        private GestureDetector gestureDetector;
        private GalleryAdapter.ClickListener clickListener;

        public RecyclerTouchListener(Context context, final RecyclerView recyclerView, final GalleryAdapter.ClickListener clickListener) {
            this.clickListener = clickListener;

            gestureDetector = new GestureDetector(context, new GestureDetector.SimpleOnGestureListener() {
                @Override
                public boolean onSingleTapUp(MotionEvent e) {
                    return true;
                }

                @Override
                public void onLongPress(MotionEvent e) {
                    View child = recyclerView.findChildViewUnder(e.getX(), e.getY());
                    if (child != null && clickListener != null) {
                        clickListener.onLongClick(child, recyclerView.getChildPosition(child));
                    }
                }
            });
        }
        @Override
        public boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent e) {

            View child = rv.findChildViewUnder(e.getX(), e.getY());
            if (child != null && clickListener != null && gestureDetector.onTouchEvent(e)) {
                clickListener.onClick(child, rv.getChildPosition(child));
            }
            return false;
        }
        @Override
        public void onTouchEvent(RecyclerView rv, MotionEvent e) {
        }

        @Override
        public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) {

        }
    }

Answer 1

This should probably solve your problem. You've a method called getFirstVisiblePosition() which lets you get the first item in the list that goes on screen so you can set the textview accordingly. Take a look at the example here Get visible items in RecyclerView . Hope that helps