Recycle bitmaps on a listview causes issues

Question

I got a list view where im displaying images, these images are downloaded and cache properly. As I scroll down the list and load new items I want to recycle the least recently used ones to save on memory. I have successfully implemented the LRU Map and im calling recycle on bitmaps which are not visible on the screen. Here is part of the code:

imageView is a ViewGroup

public void recycleImage(int res) {
    if (imageView != null) {
        imageView.setBackgroundDrawable(null);
        if (res > 0)
            imageView.setBackgroundResource(res);
    }

    if (bitmap != null && !bitmap.isRecycled()) {
        bitmap.recycle();

        Log.i(TAG, "Bitmap recycled");
    }
}

Those values are saved on the getView method of the adapter. The problem is that as I recycle images I can see how the ones visible on the screen also get lost (note im only recycling the ones I know are out of the screen).

Does anyone have an idea of why im losing the images currently displayed when I recycled the bitmaps of others on the listview?

This is where I access the stored bitmap or download it.

   if (mImageMap.containsKey(url)) { 
       ImageCacheModel cache = mImageMap.get(url); 
       return cache.getBitmap(); 
   } else if (cacheManager.isUrlCached(url)) { 
       mImageMap.put(url, new ImageCacheModel(imageView, cacheManager.getCachedBitmapOrNull(url, 2)));

        ImageCacheModel cache = mImageMap.get(url);
        return cache.getBitmap();
    } else {
        cacheManager.addUrlToQueue(url, this, true);
    }

Answer 1

You must remember that your ImageView inside your convertView (list element) is being reused all the time. In short you don't create a new convertView every time a new view shows up from the ListView you actually just reuse the last element that scrolled out.

So in your case lets say you have a list where 3 items are visible at any time. When you clear item 1 you also clear item 4 and item 7 etc. etc.

I can't point to the exact point where this issue bites you but based on what you describe I'm almost certain this is the issue.