Android lazy load images, ambiguous points?

Question

I found some code from the web for lazy loading of images and i used it in my app. I have following troubles understanding the code. I've read many other posts about this but none helped. My questions are:

1. According to the code below, at which point does the getView method return a view? I mean the app first sets default picture then goes for loading the actual image from url or file cache. So logically getView must return the view two times, once for default picture and once for actual picture. Is this true? How is the procedure?
2. What happens inside imageViewReused() method? Each pair of (imageView, url) is put in a map right away it is inserted to the process (DisplayImage), but later at imageViewReused(), it is compared to a url from the very same imageView pair? Shouldn't these always be the same? I know that when the listView is scrolled, no new imageView is created but the one which is getting fired from listView, is recycled. Even considering this, still we have a pair with same imageView, but new url which will be replace with the old url in the map. So what is the purpose of if statement in imageViewReused()? In other words, what if i omit the if statement so that the method always returns false? I've done this actually and no effect was observed in the app performance!
3. Scrolling a little fast or for 3 or more times repeatedly, the app simply crashes. LogCat says outOfMemoryException. How to deal with it? Note that the holder pattern is used in the code.

Below is my code:

public class ImageLoader {

MemoryCache memoryCache = new MemoryCache();
FileCache fileCache;
private Map<ImageView, String> imageViews = Collections
        .synchronizedMap(new WeakHashMap<ImageView, String>());
ExecutorService executorService;
Handler handler = new Handler();

public ImageLoader(Context context) {
    fileCache = new FileCache(context);
    executorService = Executors.newFixedThreadPool(5);
}

final int stub_id = R.drawable.profile;

public void DisplayImage(String url, ImageView imageView) {
    imageViews.put(imageView, url);
    Bitmap bitmap = memoryCache.get(url);
    if (bitmap != null)
        imageView.setImageBitmap(bitmap);
    else {
        queuePhoto(url, imageView);
        imageView.setImageResource(stub_id);
    }
}

private void queuePhoto(String url, ImageView imageView) {
    PhotoToLoad p = new PhotoToLoad(url, imageView);
    executorService.submit(new PhotosLoader(p));
}
private Bitmap getBitmap(String url) {
    File f = fileCache.getFile(url);

    // from SD cache
    Bitmap b = decodeFile(f);
    if (b != null)
        return b;

    // from web
    try {
        Bitmap bitmap = null;
        URL imageUrl = new URL(url);
        HttpURLConnection conn = (HttpURLConnection) imageUrl
                .openConnection();
        conn.setConnectTimeout(30000);
        conn.setReadTimeout(30000);
        conn.setInstanceFollowRedirects(true);
        InputStream is = conn.getInputStream();
        OutputStream os = new FileOutputStream(f);
        Utils.CopyStream(is, os);
        os.close();
        conn.disconnect();
        bitmap = decodeFile(f);
        return bitmap;
    } catch (Throwable ex) {
        ex.printStackTrace();
        if (ex instanceof OutOfMemoryError)
            memoryCache.clear();
        return null;
    }
}

// decodes image and scales it to reduce memory consumption
private Bitmap decodeFile(File f) {
    try {
        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        FileInputStream stream1 = new FileInputStream(f);
        BitmapFactory.decodeStream(stream1, null, o);
        stream1.close();

        final int REQUIRED_SIZE = 70;
        int width_tmp = o.outWidth, height_tmp = o.outHeight;
        int scale = 1;
        while (true) {
            if (width_tmp / 2 < REQUIRED_SIZE
                    || height_tmp / 2 < REQUIRED_SIZE)
                break;
            width_tmp /= 2;
            height_tmp /= 2;
            scale *= 2;
        }

        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize = scale;
        FileInputStream stream2 = new FileInputStream(f);
        Bitmap bitmap = BitmapFactory.decodeStream(stream2, null, o2);
        stream2.close();
        return bitmap;
    } catch (FileNotFoundException e) {
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

// Task for the queue
private class PhotoToLoad {
    public String url;
    public ImageView imageView;

    public PhotoToLoad(String u, ImageView i) {
        url = u;
        imageView = i;
    }
}

class PhotosLoader implements Runnable {
    PhotoToLoad photoToLoad;

    PhotosLoader(PhotoToLoad photoToLoad) {
        this.photoToLoad = photoToLoad;
    }

    @Override
    public void run() {
        try {
            if (imageViewReused(photoToLoad))
                return;
            Bitmap bmp = getBitmap(photoToLoad.url);
            memoryCache.put(photoToLoad.url, bmp);
            if (imageViewReused(photoToLoad))
                return;
            BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad);
            handler.post(bd);
        } catch (Throwable th) {
            th.printStackTrace();
        }
    }
}

boolean imageViewReused(PhotoToLoad photoToLoad) {
    String tag = imageViews.get(photoToLoad.imageView);
    if (tag == null || !tag.equals(photoToLoad.url))
        return true;
    return false;
}

// Used to display bitmap in the UI thread
class BitmapDisplayer implements Runnable {
    Bitmap bitmap;
    PhotoToLoad photoToLoad;

    public BitmapDisplayer(Bitmap b, PhotoToLoad p) {
        bitmap = b;
        photoToLoad = p;
    }

    public void run() {
        if (imageViewReused(photoToLoad))
            return;
        if (bitmap != null)
            photoToLoad.imageView.setImageBitmap(bitmap);
        else
            photoToLoad.imageView.setImageResource(stub_id);
    }
}
public void clearCache() {
    memoryCache.clear();
    fileCache.clear();
}
}

Answer 1

I would recommend something like fresco (which even supports off Heap Image storing), Glide or Picasso, which are highly optimized Android Image Loading Libraries. I'm generally against including a library for everything but for image loading you want to be fast and bug free. One simple class can't offer this