Question

I have the following code running on my Android device. It works great and displays my list items wonderfully. It’s also clever in the fact it only downloads the data when it’s needed by the ArrayAdapter. However, whilst the download of the thumbnail is occurring, the entire list stalls and you cannot scroll until it’s finished downloading. Is there any way of threading this so it’ll still scroll happily, maybe show a place holder for the downloading image, finish the download, and then show?

I think I just need to put my downloadImage class into it’s own thread so its executed separately from the UI. But how to add this into my code is the mystery!

Any help with this would be really appreciated.

private class CatalogAdapter extends ArrayAdapter<SingleQueueResult> {

    private ArrayList<SingleQueueResult> items;

    //Must research what this actually does!
    public CatalogAdapter(Context context, int textViewResourceId, ArrayList<SingleQueueResult> items) {
        super(context, textViewResourceId, items);
        this.items = items;

    }

    /** This overrides the getview of the ArrayAdapter. It should send back our new custom rows for the list */
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        View v = convertView;
        if (v == null) {
            LayoutInflater vi = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = vi.inflate(R.layout.mylists_rows, null);

        }
        final SingleQueueResult result = items.get(position);
        // Sets the text inside the rows as they are scrolled by!
        if (result != null) {

            TextView title = (TextView)v.findViewById(R.id.mylist_title);
            TextView format = (TextView)v.findViewById(R.id.mylist_format);
            title.setText(result.getTitle());
            format.setText(result.getThumbnail());

            // Download Images
            ImageView myImageView = (ImageView)v.findViewById(R.id.mylist_thumbnail);
            downloadImage(result.getThumbnail(), myImageView);

        }

        return v;
    }
}

// This should run in a seperate thread
public void downloadImage(String imageUrl, ImageView myImageView) {

    try {
        url = new URL(imageUrl);
        URLConnection conn = url.openConnection();
        conn.connect();
        InputStream is = conn.getInputStream();
        BufferedInputStream bis = new BufferedInputStream(is);
        Bitmap bm = BitmapFactory.decodeStream(bis);
        bis.close();
        is.close();
        myImageView.setImageBitmap(bm);
    } catch (IOException e) {
        /* Reset to Default image on any error. */
        //this.myImageView.setImageDrawable(getResources().getDrawable(R.drawable.default));
    }
}

Answer 1

Here’s a simplified version of what I’m using in my apps:

// this lives in Application subclass and is reused
public static final ExecutorService EXECUTOR = Executors.newSingleThreadExecutor();

// the method itself

    public void attachImage(final String fileUrl, final ImageView view) {
        EXECUTOR.execute(new Runnable() {

            @Override
            public void run() {
                final Drawable image = methodThatGetsTheImage(fileUrl);
                if (image != null) {
                    view.post(new Runnable() {

                        @Override
                        public void run() {
                            view.setImageDrawable(drawable);
                        }
                    });
                }
            }
        });
    }