Question

I need help understanding androids LruCache. I want to use to load images into my gridview in order make the loading/scrolling better. Can someone post an example code using LruCache please. Thanks in advance.

Answer 1

Below is a class I made for using LruCache, this is based on the presentation Doing More With Less: Being a Good Android Citizen given at Google I/O 2012.

Check out the movie for more information about what I’m doing in the TCImageLoader class:

public class TCImageLoader implements ComponentCallbacks2 {
    private TCLruCache cache;

    public TCImageLoader(Context context) {
        ActivityManager am = (ActivityManager) context.getSystemService(
            Context.ACTIVITY_SERVICE);
        int maxKb = am.getMemoryClass() * 1024;
        int limitKb = maxKb / 8; // 1/8th of total ram
        cache = new TCLruCache(limitKb);
    }

    public void display(String url, ImageView imageview, int defaultresource) {
        imageview.setImageResource(defaultresource);
        Bitmap image = cache.get(url);
        if (image != null) {
            imageview.setImageBitmap(image);
        }
        else {
            new SetImageTask(imageview).execute(url);
        }
    }

    private class TCLruCache extends LruCache<String, Bitmap> {

        public TCLruCache(int maxSize) {
            super(maxSize);
        }

        @Override
        protected int sizeOf(ImagePoolKey key, Bitmap value) {
            int kbOfBitmap = value.getByteCount() / 1024;
            return kbOfBitmap;
        }
    }

    private class SetImageTask extends AsyncTask<String, Void, Integer> {
        private ImageView imageview;
        private Bitmap bmp;

        public SetImageTask(ImageView imageview) {
            this.imageview = imageview;
        }

        @Override
        protected Integer doInBackground(String... params) {
            String url = params[0];
            try {
                bmp = getBitmapFromURL(url);
                if (bmp != null) {
                    cache.put(url, bmp);
                }
                else {
                    return 0;
                }
            } catch (Exception e) {
                e.printStackTrace();
                return 0;
            }
            return 1;
        }

        @Override
        protected void onPostExecute(Integer result) {
            if (result == 1) {
                imageview.setImageBitmap(bmp);
            }
            super.onPostExecute(result);
        }

        private Bitmap getBitmapFromURL(String src) {
            try {
                URL url = new URL(src);
                HttpURLConnection connection
                    = (HttpURLConnection) url.openConnection();
                connection.setDoInput(true);
                connection.connect();
                InputStream input = connection.getInputStream();
                Bitmap myBitmap = BitmapFactory.decodeStream(input);
                return myBitmap;
            } catch (IOException e) {
                e.printStackTrace();
                return null;
            }
        }

    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
    }

    @Override
    public void onLowMemory() {
    }

    @Override
    public void onTrimMemory(int level) {
        if (level >= TRIM_MEMORY_MODERATE) {
            cache.evictAll();
        }
        else if (level >= TRIM_MEMORY_BACKGROUND) {
            cache.trimToSize(cache.size() / 2);
        }
    }
}