Images are repeating in ListView

Question

I have implemented android app which should download images from server and display them in ListView, but very interesting thing occures while images are downloading

Answer 1

i had this issue and implemented lruCache ...i believe you need api 12 and above or use the compatiblity v4 library. lurCache is fast memory but it also has a budget, so if your worried about that you can use a diskcache ...its all described here http://developer.android.com/training/displaying-bitmaps/cache-bitmap.html

I'll now provide my implementation which is a singleton i call from anywhere like this:

//where first is a string and other is a imageview to load

DownloadImageTask.getInstance().loadBitmap(avatarURL, iv_avatar); 

here's the ideal code to cache and then call the above in getView of an adapter when retrieving the web image:

 public class DownloadImageTask {

private LruCache mMemoryCache;

/* create a singleton class to call this from multiple classes */

private static DownloadImageTask instance = null;

public static DownloadImageTask getInstance() {
    if (instance == null) {
        instance = new DownloadImageTask();
    }
    return instance;
}

//lock the constructor from public instances
private DownloadImageTask() {

    // Get max available VM memory, exceeding this amount will throw an
    // OutOfMemory exception. Stored in kilobytes as LruCache takes an
    // int in its constructor.
    final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);

    // Use 1/8th of the available memory for this memory cache.
    final int cacheSize = maxMemory / 8;

    mMemoryCache = new LruCache(cacheSize) {
        @Override
        protected int sizeOf(String key, Bitmap bitmap) {
            // The cache size will be measured in kilobytes rather than
            // number of items.
            return bitmap.getByteCount() / 1024;
        }
    };

}

public void loadBitmap(String avatarURL, ImageView imageView) {
    final String imageKey = String.valueOf(avatarURL);

    final Bitmap bitmap = getBitmapFromMemCache(imageKey);
    if (bitmap != null) {
        imageView.setImageBitmap(bitmap);
    } else {
        imageView.setImageResource(R.drawable.ic_launcher);

        new DownloadImageTaskViaWeb(imageView).execute(avatarURL);
    }
}

private void addBitmapToMemoryCache(String key, Bitmap bitmap) {
    if (getBitmapFromMemCache(key) == null) {
        mMemoryCache.put(key, bitmap);
    }
}

private Bitmap getBitmapFromMemCache(String key) {
    return mMemoryCache.get(key);
}

/* a background process that opens a http stream and decodes a web image. */

class DownloadImageTaskViaWeb extends AsyncTask {
    ImageView bmImage;

    public DownloadImageTaskViaWeb(ImageView bmImage) {
        this.bmImage = bmImage;
    }

    protected Bitmap doInBackground(String... urls) {

        String urldisplay = urls[0];
        Bitmap mIcon = null;
        try {
            InputStream in = new java.net.URL(urldisplay).openStream();
            mIcon = BitmapFactory.decodeStream(in);

        } catch (Exception e) {
            Log.e("Error", e.getMessage());
            e.printStackTrace();
        }

        addBitmapToMemoryCache(String.valueOf(urldisplay), mIcon);

        return mIcon;
    }

    /* after decoding we update the view on the mainUI */
    protected void onPostExecute(Bitmap result) {
        bmImage.setImageBitmap(result);

    }

}

}