Displaying Coverart (from id3) in Recyclerview in background

Question

I am working on an app that uses a Recyclerview to display mp3 files, providing its cover art image along with other info. It works but is slow once it starts dealing with a dozen or more cover arts to retrieve, as I am currently doing this from the id3 on the main thread, which I know is not a good idea. Ideally, I would work with placeholders so that the images can be added as they become available. I've been looking into moving the retrieval to a background thread and have looked at different options: AsyncTask, Service, WorkManager. AsyncTask seems not to be the way to go as I face memory leaks (I need context to retrieve the cover art through MetadataRetriever). So I am leaning away from that. Yet I am struggling to figure out which approach is best in my case.

From what I understand I need to find an approach that allows multithreading and also a means to cancel the retrieval in case the user has already moved on (scrolling or navigating away). I am already using Glide, which I understand should help with the caching. I know I could rework the whole approach and provide the cover art as images separately, but that seems a last resort to me, as I would rather not weigh down the app with even more data.

The current version of the app is here (please note it will not run as I cannot openly divulge certain aspects). I am retrieving the cover art as follows (on the main thread):

static public Bitmap getCoverArt(Uri medUri, Context ctxt) {

    MediaMetadataRetriever mmr = new MediaMetadataRetriever();
    mmr.setDataSource(ctxt, medUri);

    byte[] data = mmr.getEmbeddedPicture();

    if (data != null) {
        return BitmapFactory.decodeByteArray(data, 0, data.length);
    } else {
        return null;
    }
}

I've found many examples with AsyncTask or just keeping the MetaDataRetriever on the main thread, but have yet to find an example that enables a dozen or more cover arts to be retrieved without slowing down the main thread. I would appreciate any help and pointers.

Answer 1

It turns out it does work with AsyncTask, as long as it is not a class onto itself but setup and called from a class with context. Here is a whittled down version of my approach (I am calling this from within my Adapter.):

//set up titles and placeholder image so we needn't wait on the image to load
titleTv.setText(selectedMed.getTitle());
subtitleTv.setText(selectedMed.getSubtitle());
imageIv.setImageResource(R.drawable.ic_launcher_foreground);
imageIv.setAlpha((float) 0.2);
final long[] duration = new long[1];

//a Caching system that helps reduce the amount of loading needed. See: https://github.com/cbonan/BitmapFun?files=1
if (lruCacheManager.getBitmapFromMemCache(selectedMed.getId() + position) != null) {

//is there an earlier cached image to reuse? imageIv.setImageBitmap(lruCacheManager.getBitmapFromMemCache(selectedMed.getId() + position)); imageIv.setAlpha((float) 1.0);

        titleTv.setVisibility(View.GONE);
        subtitleTv.setVisibility(View.GONE);
    } else {

        //time to load and show the image. For good measure, the duration is also queried, as this also needs the setDataSource which causes slow down
        new AsyncTask<Uri, Void, Bitmap>() {
            @Override
            protected Bitmap doInBackground(Uri... uris) {
                MediaMetadataRetriever mmr = new MediaMetadataRetriever();
                mmr.setDataSource(ctxt, medUri);
                byte[] data = mmr.getEmbeddedPicture();
                Log.v(TAG, "async data: " + Arrays.toString(data));

                String durationStr = mmr.extractMetadata(MediaMetadataRetriever.METADATA_KEY_DURATION);
                duration[0] = Long.parseLong(durationStr);

                if (data != null) {
                    InputStream is = new ByteArrayInputStream(mmr.getEmbeddedPicture());
                    return BitmapFactory.decodeStream(is);
                } else {
                    return null;
                }
            }

            @Override
            protected void onPostExecute(Bitmap bitmap) {
                super.onPostExecute(bitmap);

                durationTv.setVisibility(View.VISIBLE);
                durationTv.setText(getDisplayTime(duration[0], false));

                if (bitmap != null) {
                    imageIv.setImageBitmap(bitmap);
                    imageIv.setAlpha((float) 1.0);

                    titleTv.setVisibility(View.GONE);
                    subtitleTv.setVisibility(View.GONE);
                } else {
                    titleTv.setVisibility(View.VISIBLE);
                    subtitleTv.setVisibility(View.VISIBLE);
                }

                lruCacheManager.addBitmapToMemCache(bitmap, selectedMed.getId() + position);
            }
        }.execute(medUri);
    }

I have tried working with Glide for the caching, but I haven't been able to link the showing/hiding of the TextViews to whether there is a bitmap. In a way though, this is sleeker as I don't need to load the bulk of the Glide-library. So I am happy with this for now.