Listview catching plenty on scroll

Question

My Listview is crashing enough on the scroll, I tried to implement Viewholder to the Adapter but did not solve, could help me?

Adapter:

public class Adapter extends SimpleAdapter {
    private Context context;
    public LayoutInflater inflater = null;

    public Adapter(Context context, List<? extends Map<String, ?>> data, int resource, String[] from, int[] to)
    {
        super(context, data, resource, from, to);

        inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    @Override
    public View getView(int position, View view, ViewGroup parent) {
        ViewHolder viewHolder;

        HashMap<String, Object> data = (HashMap<String, Object>) super.getItem(position);

        if(view == null){
            view = inflater.inflate(R.layout.clientes, parent, false);

            viewHolder = new ViewHolder();

            viewHolder.thumbnail = (ImageView) view.findViewById(R.id.thumbnail);
            viewHolder.title = (TextView)view.findViewById(R.id.title);
            viewHolder.content = (TextView)view.findViewById(R.id.content);

            view.setTag(viewHolder);
        }else{
            viewHolder = (ViewHolder)view.getTag();
        }

        try {
            viewHolder.thumbnail.setImageBitmap( new DownloadTask().execute(data.get("thumbnail").toString()).get());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }

        viewHolder.title.setText(data.get("title").toString());
        viewHolder.content.setText(data.get("content").toString());

        return view;
    }

    static class ViewHolder{
        ImageView thumbnail;
        TextView title;
        TextView content;
    }
}

Downloadtask:

public class DownloadTask extends AsyncTask<String, Void, Bitmap> {

    @Override
    protected void onPreExecute() {}

    @Override
    protected Bitmap doInBackground(String... params) {
        Bitmap image = null;

        try {
            image = BitmapFactory.decodeStream( new URL(params[0]).openConnection().getInputStream());
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        return image;
    }
}

Answer 1

I believe your problem may be this one:

viewHolder.thumbnail.setImageBitmap( new DownloadTask().execute(data.get("thumbnail").toString()).get());

I’m guessing because I’m not seeing your implementation of the Downloadtask. On Android all operations are performed on Main Thread, which is the thread of the UI. If you are doing any Bitmap operation on this thread surely your Viewholder will be very slow and may even lock the application.

EDIT: We have seen that the problem was even the Downloadtask, but now you are having problems to properly manage the cache of your Bitmaps. To not get off topic I suggest you open a new discussion and call this one off. It is suggested to analyze some solution already tested in some code, as the Universal Loader.

Answer 2

The problem is that the method get() of Asynctask only returns when the method doInBackground() end. You are using the Asynctask synchronously.

Change the class Downloadtask in order to receive the viewHolder.thumbnail and do the setImageBitmap() in the method onPostExecute().

public class DownloadTask extends AsyncTask<String, Void, Bitmap> {
    private final WeakReference<ImageView> imageView;

    public DownloadTask(ImageView thumbnail) {
        imageView = new WeakReference<ImageView>(thumbnail);
    }

    @Override
    protected Bitmap doInBackground(String... params) {
        Bitmap image = null;

        try {
            image = BitmapFactory.decodeStream( new URL(params[0]).openConnection().getInputStream());
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        return image;
    }

    @Override
    protected void onPostExecute(Bitmap bitmap) {

        ImageView thumbnail = imageView.get();
        if (thumbnail != null) {
            if (bitmap != null) {
                thumbnail.setImageBitmap(bitmap);
            }
        }
    }
}

In the Adapter change the line

viewHolder.thumbnail.setImageBitmap(new DownloadTask()
                       .execute(data.get("thumbnail").toString()).get());

for

new DownloadTask(viewHolder.thumbnail).execute(data.get("thumbnail").toString());