How to create an ImageLoader for a huge amount of images on Android

Hi there!

During development with a huge amount of images, most of all image loaders available out there, does not display(caches) the images smoothlty. For this reason, i have tryed to put all the code "pieces" i found in the internet together to get a almost perfect image loader for my application. The result is shown bellow. It works very well for me. It may be also interesting for other developers. Here is my solution:

The Loader interface

/**
 * Drawable loader used to create and cache thumbnails while presenting it in a gallery preview.
 * IMPORTANT: instantiate it in your main activity like this:
 * 
 * protected void onCreate(final Bundle savedInstanceState) {
 *       super.onCreate(savedInstanceState);
 *       ...
 *       DrawableLoader.getInstance(this);
 *       ...
 *   }
 * 
 * 
* @author Ricardo Ferreira
 * @version 1.0
 * @since 03/04/2014
 */
public interface Loader {
    
    /**
     * Clears all instance data and stops running threads
     */
    public void Reset() ;
    /**
     * Loads a drawable into an image. Call this method inside of getView(...) from your concrete 
     * implementation of BaseAdapter.
     *      * public View getView(int position, View convertView, ViewGroup parent){
     * ...
     * String url = PATH_FILE + pathImage;// path to your storage like "/storage/..."
     * ImageView imageView = (ImageView)holder.imgView;
     * final Drawable placeholder = mContext.getResources().getDrawable(R.drawable.placeholder);
     * DrawableLoader.getInstance(mContext).loadDrawable(url, imageView, placeholder);
     * ...
     * }
     * 
* @param url file path to the storage location
     * @param imageView the image to be presented in a list view or grid view
     * @param placeholder the place holder image to be shown, while the loading is running.
     */
    public void loadDrawable(final String url, final ImageView imageView, Drawable placeholder);

}

The Loader implementation

/**
 * Drawable loader used to create and cache thumbnails while presenting it in a gallery preview.
 * IMPORTANT: instantiate it in your main activity like this:
 * 
 * protected void onCreate(final Bundle savedInstanceState) {
 *       super.onCreate(savedInstanceState);
 *       ...
 *       DrawableLoader.getInstance(this);
 *       ...
 *   }
 * 
 * 
* @author Ricardo Ferreira
 * @version 1.0
 * @since 03/04/2014
 */
@SuppressLint("HandlerLeak")
public class DrawableLoader implements Loader{

    private final Map < String, SoftReference < Drawable > > mCache = new HashMap < String, SoftReference < Drawable > >();
    private final LinkedList < Drawable > mChacheController = new LinkedList < Drawable > ();
    private ExecutorService mThreadPool;
    private final Map < ImageView, String > mImageViews = Collections.synchronizedMap(new WeakHashMap < ImageView, String >());
    public final static int MAX_CACHE_SIZE = 1024;
    public final int THREAD_POOL_SIZE = 5;
    private Context mContext;
    private static Loader loader;
    
    // SINGLETON
    private DrawableLoader(Context context) {
        mThreadPool = Executors.newFixedThreadPool(THREAD_POOL_SIZE);
        mContext=context;
    }
    
    public static Loader getInstance(Context ctx){
        if(loader==null){
            loader =  new DrawableLoader(ctx);
        }
        return loader;
    }
    
    public void Reset() {
        ExecutorService oldThreadPool = mThreadPool;
        mThreadPool = Executors.newFixedThreadPool(THREAD_POOL_SIZE);
        oldThreadPool.shutdownNow();
        mChacheController.clear();
        mCache.clear();
        mImageViews.clear();
    }
    
    public void loadDrawable(final String url, final ImageView imageView, Drawable placeholder) {
        mImageViews.put(imageView, url);
        Drawable drawable = getDrawableFromCache(url);
        if (drawable != null) {
            imageView.setImageDrawable(drawable);
        } else {
            imageView.setImageDrawable(placeholder);
            queueJob(url, imageView, placeholder);
        }
    }

    private Drawable getDrawableFromCache(String url) {
        if (mCache.containsKey(url)) {
            return mCache.get(url).get();
        }
        return null;
    }

    private synchronized void putDrawableInCache(String url, Drawable drawable) {
        int chacheControllerSize = mChacheController.size();
        if (chacheControllerSize > MAX_CACHE_SIZE){
            mChacheController.subList(0, MAX_CACHE_SIZE / 2).clear();
        }
        mChacheController.addLast(drawable);
        mCache.put(url, new SoftReference(drawable));

    }

    private void queueJob(final String url, final ImageView imageView, final Drawable placeholder) {
        /* Create handler in UI thread. */
        final Handler handler = new Handler() {
            @Override
            public void handleMessage(Message msg) {
                String tag = mImageViews.get(imageView);
                if (tag != null && tag.equals(url)) {
                    if (imageView.isShown())
                        if (msg.obj != null) {
                            imageView.setImageDrawable((Drawable) msg.obj);
                        } else {
                            imageView.setImageDrawable(placeholder);
                        }
                }
            }
        };

        mThreadPool.submit(new Runnable() {
            @Override
            public void run() {
                final Drawable bmp = downloadDrawable(url);
                // if the view is not visible anymore, 
                //the image will be ready for next time in cache
                if (imageView.isShown()) {
                    Message message = Message.obtain();
                    message.obj = bmp;
                    handler.sendMessage(message);
                }
            }
        });
    }
    
    private Drawable downloadDrawable(String url) {
            final Bitmap decodeBitmap = ViewHelper.decodeBitmap(url.replaceAll("file://", ""), 100);
            Drawable drawable = new BitmapDrawable(mContext.getResources(), decodeBitmap);
            putDrawableInCache(url, drawable);
            return drawable;
    }
    
    /** pass new URL(urlString) to it, while urlString is the path to the drawable like:
     *  http://www.google.com.br/images/your_image.png
     */
    protected Drawable downloadDrawable(URL url) {
        try {
            InputStream is = getInputStream(url);

            Drawable drawable = Drawable.createFromStream(is, url.getPath());
            putDrawableInCache(url.getPath(), drawable);
            return drawable;

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }

    private InputStream getInputStream(URL url) throws MalformedURLException, IOException {
        //URL url = new URL(urlString);
        URLConnection connection;
        connection = url.openConnection();
        connection.setUseCaches(true);
        connection.connect();
        InputStream response = connection.getInputStream();

        return response;
    }
}

That's all. Hope you like it! ;)

😱👇 PROMOTIONAL DISCOUNT: BOOKS AND IPODS PRO 😱👇

Be sure to read, it will change your life!

Show your work by Austin Kleon: https://amzn.to/34NVmwx

This book is a must read - it will put you in another level! (Expert)

Agile Software Development, Principles, Patterns, and Practices: https://amzn.to/30WQSm2

Write cleaner code and stand out!

Clean Code - A Handbook of Agile Software Craftsmanship: https://amzn.to/33RvaSv

This book is very practical, straightforward and to the point! Worth every penny!

Kotlin for Android App Development (Developer's Library): https://amzn.to/33VZ6gp

Needless to say, these are top right?

Apple AirPods Pro: https://amzn.to/2GOICxy

😱👆 PROMOTIONAL DISCOUNT: BOOKS AND IPODS PRO 😱👆

Clean Code Development - Quality Seal

Thursday, April 3, 2014