Load Image to recyclerview by asynctask and retrofit

Question

My LoadImageTask class:

    private class LoadImageTask extends AsyncTask<Integer,Void,String>
{

String string;
WeakReference<ImageView> imageViewWeakReference;

    public LoadImageTask(ImageView imageView) {
        imageViewWeakReference = new WeakReference<ImageView>(imageView);
    }

    @Override
    protected String doInBackground(Integer... params) {

        //get image default
        mService.getExhibitImageById(params[0], true).enqueue(new Callback<String>() {
            @Override
            public void onResponse(Call<String> call, Response<String> response) {

                if (response.isSuccessful()) {
                    try{
                        string = response.body();
                        Log.d("AnswersPresenter", "Image loaded!!!!");
                    }
                    catch (Exception e)
                    {
                        e.printStackTrace();
                    }

                } else {
                    int statusCode = response.code();
                    Toast.makeText(mContext, "Error" + statusCode + response.message(), Toast.LENGTH_SHORT).show();
                }

            }


            @Override
            public void onFailure(Call<String> call, Throwable t) {
                showErrorMessage();
                Log.d("AnswersPresenter", "error loading image!!!");

            }
        });
        return string;
    }

    @Override
    protected void onPostExecute(String string) {
        super.onPostExecute(string);
        if (string !=null && imageViewWeakReference !=null)
        {
            ImageView imv =imageViewWeakReference.get();
            if (imv!=null)
            {
                Bitmap bitmap = Util.StringToBitMap(string);
                imv.setImageBitmap(bitmap);
            }
        }

    }
}

I use retrofit inside method doInBackground() to get a string encoded of image by id from api: http://demo.museum.vebrary.vn/api/Exhibit/GetImage?id=3 With id is got in

@Override
public void onBindViewHolder(Adapter.ViewHolder holder, int position) {

    ExhibitMainScreenModel item = ExhibitList.get(position);
    TextView tvName = holder.tvName;
    tvName.setText(item.getEXHIBITNAME());
    TextView tvDesc = holder.tvDescription;
    tvDesc.setText(item.getDESCRIPTION());
    ImageView imv = holder.imvExhibit;

    /*//get ID and load image by id
    id = item.getEXHID();
    loadImage(id,holder);*/
    id = item.getEXHID();
    LoadImageTask task = new LoadImageTask(holder.imvExhibit);
    task.execute(id);


}

doInBackground return a string encode of image and in void onPostExecute(String string) I use

public static Bitmap StringToBitMap(String encodedString){
    try{
        byte [] encodeByte=Base64.decode(encodedString,Base64.DEFAULT);
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inSampleSize = 8;
        Bitmap bitmap= BitmapFactory.decodeByteArray(encodeByte, 0, encodeByte.length,options);
        return bitmap;
    }catch(Exception e){
        e.getMessage();
        return null;
    }
}

change it to bitmap to display imageview. But doInBackGround return string = null; While I debug, string in

@Override
        public void onResponse(Call<String> call, Response<String> response) {

            if (response.isSuccessful()) {
                try{
                    string = response.body();
                    Log.d("AnswersPresenter", "Image loaded!!!!");
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                }

            } else {
                int statusCode = response.code();
                Toast.makeText(mContext, "Error" + statusCode + response.message(), Toast.LENGTH_SHORT).show();
            }

string = "/9j/4AAQSkZJRgABAgEASABIAAD/4RG1RXhpZgA..." , this is a encoded string. i don't know why string in return was null? Can you tell me the right way? thank you very much!

Answer 1

Method enqueue(Callback callback) asynchronously send the request and notify callback of its response or if an error occurred talking to the server, creating the request, or processing the response.

In your case "return string" get called before new Callback() class