How does Glide load image asynchronously?

Question

I have a RecyclerView and each item of RecyclerView is having ImageView. I am loading the image in that ImageView using Glide. I saw some blog says Glide can load image asynchronously but I can not see this from the code below. It seems it only load one image when onBindViewHolder is invoked. How does it show asynchrony?

   public class GalleryAdapter extends RecyclerView.Adapter<GalleryAdapter.ViewHolder> {
        private Context mContext;
        private List<GalleryItem> mList;

        public GalleryAdapter(Context mContext, List<GalleryItem> mList) {
            this.mContext = mContext;
            this.mList = mList;
        }

        public static class ViewHolder extends RecyclerView.ViewHolder {
            public ImageView mImageView;
            public ViewHolder(View itemView) {
                super(itemView);
                mImageView = (ImageView) itemView.findViewById(R.id.gallery_item);
            }
        }

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

        @Override
        public void onBindViewHolder(ViewHolder holder, int position) {
            GalleryItem item = mList.get(position);
            holder.mImageView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {

                }
            });
            Glide.with(mContext)
                    .load(item.getUrl())
                    .thumbnail(0.5f)
                    .into(holder.mImageView);
        }

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

        public void addAll(List<GalleryItem> newList) {
            mList.addAll(newList);
        }

        public void clear() {
            mList.clear();
        }
    }

Answer 1

According to glide documentation here and here you should use the into() method that returns FutureTarget and not the one that returns a Target. This method take width and height, not an ImageView : "If you actually want to interact with a decoded image on a background thread, instead of using downloadOnly you can use the version of into() that returns a FutureTarget."