Loading image bitmap from content providers using asynctask

Question

I have been trying to query for all images on sd card through MediaStore content provider and display their thumbnail on a GridView.

However, if i load the image thumbnail on the main thread, the scrolling gets incredibly slow...

So i tried to load the bitmap through asynctasks: Scrolling performance got better, but now the grid items keep reloading their thumbnail until it gets the correct bitmap...

Here is my asynctask, which loads the bitmaps:

package x.y;

import java.lang.ref.WeakReference;

import android.content.ContentResolver;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory.Options;
import android.os.AsyncTask;
import android.provider.MediaStore;
import android.widget.ImageView;

public class ImageThumbnailLoader extends AsyncTask<Long, Void, Bitmap> {

    private final Options mOptions;

    private WeakReference<ImageView> mImageViewWeakReference;
    private ContentResolver mContentResolver;

        public ImageThumbnailLoader(ImageView imageView,
                ContentResolver cr) {
        mContentResolver = cr;
        mImageViewWeakReference = new WeakReference<ImageView>(imageView);
        mOptions = new Options();
        mOptions.inSampleSize = 4;
    }



    @Override
    protected Bitmap doInBackground(Long... params) {
        Bitmap result;
            result = MediaStore.Images.Thumbnails.getThumbnail(
                    mContentResolver, params[0],
                    MediaStore.Images.Thumbnails.MINI_KIND, mOptions);
        return result;
    }

    @Override
    protected void onPostExecute(Bitmap result) {
        super.onPostExecute(result);
            if (mImageViewWeakReference != null
                    && mImageViewWeakReference.get() != null)
                mImageViewWeakReference.get().setImageBitmap(result);
    }

}

And here is my custom cursor adapter:

package x.y;

import android.content.Context;
import android.database.Cursor;
import android.graphics.BitmapFactory.Options;
import android.provider.MediaStore;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CursorAdapter;
import android.widget.ImageView;

public class MediaCursorAdapter extends CursorAdapter {

    private LayoutInflater mInflater;
    private final static int mColumnID = 0;
    private Options mOptions;

    public MediaCursorAdapter(Context context, Cursor c) {
        super(context, c);

        mInflater = LayoutInflater.from(context);
        mOptions = new Options();
        mOptions.inSampleSize = 4;
    }

    @Override
    public void bindView(View view, Context context, Cursor cursor) {

        ViewHolder holder = (ViewHolder) view.getTag();
        ImageThumbnailLoader imageLoader = new ImageThumbnailLoader(holder.thumbImg,
                context.getContentResolver());
        imageLoader.execute(cursor.getLong(mColumnID));
//      holder.thumbImg.setImageBitmap(MediaStore.Images.Thumbnails.getThumbnail(
//                  context.getContentResolver(), cursor.getLong(mColumnID),
//                  MediaStore.Images.Thumbnails.MINI_KIND, mOptions));
        Log.i("Prototype", "bindView : " + cursor.getPosition());
    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup parent) {
        Log.i("Prototype", "newView : " + cursor.getPosition());
        View view = mInflater.inflate(R.layout.grid_item, null);
        ViewHolder holder = new ViewHolder(view);
        view.setTag(holder);
        return view;
    }


    private static class ViewHolder {
        ImageView thumbImg, dragImg;

        ViewHolder(View base) {
            thumbImg = (ImageView) base.findViewById(R.id.thumbImage);
            dragImg = (ImageView) base.findViewById(R.id.dragImage);
        }
    }

}

I query the cursor with this code and send it to the adapter:

query(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, new String[] { MediaStore.Images.Media._ID,
            MediaStore.Images.Media.DATA }, null, null,
    MediaStore.Images.Media._ID);

Looks like the bindview() on my custom cursor adapter gets called more often than it is supposed to... Anyone knows how can i make the images on my gridview stop reloading while mantaining the scrolling performance??

Thanks in advance.

Answer 1

Problem solved, had to check if image at the start of async task was the same as the image at the end of it, on onPostExecute().

new bindView:

@Override
    public void bindView(View view, Context context, Cursor cursor) {

        ViewHolder holder = (ViewHolder) view.getTag();
        holder.thumbImg.setId(cursor.getPosition());
        ImageThumbnailLoader imageLoader = new ImageThumbnailLoader(holder.thumbImg,
            context.getContentResolver());
        imageLoader.execute(cursor.getLong(mColumnID));
    Log.i("Prototype", "bindView : " + cursor.getPosition());
    }

new Async:

public class ImageThumbnailLoader extends AsyncTask<Long, Void, Bitmap> {

    private final Options mOptions;

    private WeakReference<ImageView> mImageViewWeakReference;
    private ContentResolver mContentResolver;
    private int mPosition;


        public ImageThumbnailLoader(ImageView imageView,
            ContentResolver cr) {
        mContentResolver = cr;
        mImageViewWeakReference = new WeakReference<ImageView>(imageView);
        mOptions = new Options();
        mOptions.inSampleSize = 4;
        mPosition = imageView.getId();
    }



    @Override
    protected Bitmap doInBackground(Long... params) {
        Bitmap result;
            result = MediaStore.Images.Thumbnails.getThumbnail(
                mContentResolver, params[0],
                MediaStore.Images.Thumbnails.MINI_KIND, mOptions);
        return result;
    }

    @Override
    protected void onPostExecute(Bitmap result) {
        super.onPostExecute(result);
            if (mImageViewWeakReference != null
                    && mImageViewWeakReference.get() != null
                        && mPosition == mImageViewWeakReference.get().getId())
                mImageViewWeakReference.get().setImageBitmap(result);
    }

}