Question

I know this is asked before and I have already searched a lot about this but could not get any proper answer on my issue.

I have created a list, the list gets filled with data that is coming from JSON. Now inside getView() method, I am inflating my custom row with data. Each row contains a Thumbnail, and I am creating each thumbnail from a different thread.

Now the problem is, everything is going well until I don’t scroll my list. When I scroll my list, my getView() method is called continuously , and all thumbnail images are getting recreated and its position is getting shuffled. Once thumbnails are created I don’t want to recreate them and also I want to maintain the order of my thumbnails.

Can you please guys help me on this?

Any help will greatly be appreciated.

My getView() method is:

@Override
public View getView(final int position, View convertView,
                ViewGroup parent) {

            ViewHolder viewHolder = new ViewHolder();
            if (convertView == null) {
                inflater = getLayoutInflater();
                convertView = inflater.inflate(R.layout.list_item_row, parent,
                        false);
                viewHolder.titleText = (TextView) convertView
                        .findViewById(R.id.titleText);
                viewHolder.thumbImage = (ImageView) convertView
                        .findViewById(R.id.thumbnail);
                convertView.setTag(viewHolder);
            } else {
                viewHolder = (ViewHolder) convertView.getTag();
            }

            final String thumbnailURLString = mPostsList.get(position).get(
                    "thumb");
            createBitmapThread = (Thread) getLastNonConfigurationInstance();
            createBitmapThread = new MyThread(thumbnailURLString,
                    viewHolder.thumbImage);
            createBitmapThread.start();
            viewHolder.titleText.setText(title);

            return convertView;
        }

And the Thread class:

public class MyThread extends Thread {

        String mThumbURLString = null;
        ImageView mImageView = null;

        public MyThread(String thumbnailURLString, ImageView imageView) {
            mThumbURLString = thumbnailURLString;
            mImageView = imageView;
        }

        @Override
        public void run() {

                try {
                    URL newurl = null;
                    try {
                        newurl = new URL(mThumbURLString);
                    } catch (MalformedURLException e) {
                        e.printStackTrace();
                    }
                    try {
                        // Options opts = new Options();
                        /*
                         * opts.inDither = true; opts.inInputShareable = true;
                         * opts.inJustDecodeBounds = true; opts.inPurgeable =
                         * true;
                         */
                        Log.e("", "INSIDE IMAGE DOINBG");
                        mBitmap = BitmapFactory
                                .decodeStream((InputStream) newurl.getContent());
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    mHandler.post(new MyRunnable(mImageView));
                } finally {

                }


    }

    public class MyRunnable implements Runnable {

        ImageView mImageView = null;

        public MyRunnable(ImageView imageView) {
            mImageView = imageView;
        }

        public void run() {
            mImageView.setImageBitmap(mBitmap);
        }
    }

Answer 1

ok , here how i did a similar thing:

for each getView , create a new Fetching class and put it into a concurrent/synchronized stack . in the meanwhile , set the bitmap of the view to be empty (or anything else you wish) . you can also use caching instead.

the class will contain info of how to load the data (for example , the url of the bitmap) , the view to update , and the result of the fetching (for example , the bitmap itself) .

now , back to the getView, create&execute an asyncTask that will use a loop on the stack , each time it gets a Fetching class instance from the stack (once it’s empty,the asyncTask will break the loop and finish) , check that the view that needs to be updated still needs the data (using its viewHolder) load the bitmap , set the result into the Fetching class , and pass it through the publishProgress() function.

in the onProgressUpdate method , do the same check as before using the Fetching class instance and the viewHolder . if all went well , update the view to have the bitmap that was fetched .

a nice yet complicated example of how to handle the same problem can be found here .