Reputation: 803

Images are repeating in ListView

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

As you can see in video pictures which haven't been downloaded yet are represented by those which have been already downloaded. How that can happen? I've thinking about it almost two days.

http://www.youtube.com/watch?v=lxY-HAuJO0o&feature=youtu.be

here is my code of ListView adapter.

public class MoviesAdapter extends ArrayAdapter<ParkCinema> {
        private ArrayList<ParkCinema> movieDataItems;   
        private Activity context;

        public MoviesAdapter(Activity context, int textViewResourceId, ArrayList<ParkCinema> movieDataItems) {
            super(context, textViewResourceId, movieDataItems);
            this.context = context;
            this.movieDataItems = movieDataItems;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) { 
            if (convertView == null) {
                LayoutInflater vi = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                convertView = vi.inflate(R.layout.movie_data_row, null);
                }

            ParkCinema movie = movieDataItems.get(position);

            if (movie!=null){
                        ImageView imageView = (ImageView) convertView.findViewById(R.id.movie_thumb_icon);
                        String url = movie.poster();

                         if (url!=null) {
                            Bitmap bitmap = fetchBitmapFromCache(url);
                            if (bitmap==null) { 
                                new BitmapDownloaderTask(imageView).execute(url);
                            }
                            else {
                                imageView.setImageBitmap(bitmap);
                            } 
                        } 
            }
            return convertView;
        }

        private LinkedHashMap<String, Bitmap> bitmapCache = new LinkedHashMap<String, Bitmap>();

        private void addBitmapToCache(String url, Bitmap bitmap) {
            if (bitmap != null) {
                synchronized (bitmapCache) {
                    bitmapCache.put(url, bitmap);
                }
            }
        }

        private Bitmap fetchBitmapFromCache(String url) {

            synchronized (bitmapCache) {
                final Bitmap bitmap = bitmapCache.get(url);
                 if (bitmap != null) {
                    return bitmap;
                } 
            }

            return null;

        }


    private class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> {

            private String url;
            private final WeakReference<ImageView> imageViewReference;

            public BitmapDownloaderTask(ImageView imageView) {
                imageViewReference = new WeakReference<ImageView>(imageView);
            }

            @Override
            protected Bitmap doInBackground (String... source) {
                url = source[0];
                Bitmap image;
                try{
                    image = BitmapFactory.decodeStream(new URL(url).openConnection().getInputStream());
                    return image;
                    }
                catch(Exception e){Log.e("Error", e.getMessage()); e.printStackTrace();}
                return null;
                } 


            @Override
            protected void onPostExecute(Bitmap bitmap) {       
                addBitmapToCache(url, bitmap);
                imageViewReference.get().setImageBitmap(bitmap);               
            }
        }
    }

Edit 3:

public View getView(int position, View convertView, ViewGroup parent) { 
    if (convertView == null) {
        LayoutInflater vi = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
        convertView = vi.inflate(R.layout.movie_data_row, null);
        }
    ParkCinema movie = movieDataItems.get(position);
    ImageView imageView = (ImageView) convertView.findViewById(R.id.movie_thumb_icon);
    if (movie!=null){
                String url = movie.poster();

                    if (url != null) {
                        Bitmap bitmap = fetchBitmapFromCache(url);
                        if (bitmap == null) {
                            imageView.setImageResource(R.drawable.no_image);
                            new BitmapDownloaderTask(imageView).execute(url);
                        }
                        else {
                            imageView.setImageBitmap(bitmap);
                        }
                    }
                    else {
                        imageView.setImageResource(R.drawable.no_image);
                    }
                }
                else {
                    imageView.setImageResource(R.drawable.no_image);
                } 

    return convertView;

}

Upvotes: 7

Answers (6)

badal soyantar

Reputation: 1

In my case i used Picasso library instead of AsyncTask for downloading image. enter link description here

Also write if else condition, that is set null to image if url is not available

Upvotes: 0

JunaidS

Reputation: 85

I have spent hours trying to figure this one out as well...Thanks to Steven Byle's solution... Here is my solution to something similar when a user selects an item from a list:

adapter.setSelectedIndex(position);

then in the custom adapter:

public void setSelectedIndex(int ind)
{
    selectedIndex = ind;
    notifyDataSetChanged();
}

and then finally in the getView method of the adapter:

if(selectedIndex!= -1 && position == selectedIndex)
         {
             holder.tab.setBackgroundColor(Color.BLACK);
         }
         else{
             holder.tab.setBackgroundColor(Color.DKGRAY);
         }

So in conclusion make sure you assign default values

Upvotes: 0

j2emanue

Reputation: 62519

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<String, Bitmap> 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<String, Bitmap>(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<String, Void, Bitmap> {
    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);

    }

}

}

Upvotes: 1

Steven Byle

Reputation: 13269

Aha! I think I may know the issue. Right now, your getView method sets your ImageView like this:

Gets movie object at position
Pulls out the movie's thumbnail url
Using that url, it tries to find the image in the cache
If it finds the image, it sets it
If it can't find the image, it starts an async network request to go get it, and sets it after it gets downloaded.

Your issus arises since ListView reuses its rows' Views. When the first View scrolls off the screen, rather than inflate a new one, ListView passes the now offscreen row's View in as convertView for you to reuse (this is for efficiency).

When your getView gets a convertView that is getting reused, its ImageView has already been set from the row that had it before, so you see the old image from the offscreen row's View. With your current getView process, you check for the new row's image, and it doesn't find it in the cache, it starts a request to download it. While it is downloading, you see the old image until you get the new image.

To fix this, you need to make sure you set every field in the row's View immediately, to make sure you don't have any Views showing stale data. I would suggest you set the ImageView to the default drawable resource (you have set in your R.layout.movie_data_row) while you wait for the network download to get the image.

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    if (convertView == null) {
        LayoutInflater vi = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = vi.inflate(R.layout.movie_data_row, null);
    }

    ParkCinema movie = movieDataItems.get(position);
    ImageView imageView = (ImageView) convertView.findViewById(R.id.movie_thumb_icon);
    if (movie != null) {
        String url = movie.poster();

        if (url != null) {
            Bitmap bitmap = fetchBitmapFromCache(url);
            if (bitmap == null) {
                // Set the movie thumbnail to the default icon while we load
                // the real image
                imageView.setImageResource(R.drawable.movie_thumb_icon);
                new BitmapDownloaderTask(imageView).execute(url);
            }
            else {
                // Set the image to the bitmap we get from the cache
                imageView.setImageBitmap(bitmap);
            }
        }
        else {
            // Set the movie thumbnail to the default icon, since it doesn't
            // have a thumbnail URL
            imageView.setImageResource(R.drawable.movie_thumb_icon);
        }
    }
    else {
        // Set the movie thumbnail to the default icon, since there's no
        // movie data for this row
        imageView.setImageResource(R.drawable.movie_thumb_icon);
    }

-Edit-

Updated to be even more robust, using your drawable. You also have an issue with your BitmapDownloaderTask, it does not handle errors/null. Try adding this as well.

@Override
protected void onPostExecute(Bitmap bitmap) { 
    addBitmapToCache(url, bitmap);
    if (bitmap == null) {
        // Set the movie thumbnail to the default icon, since an error occurred while downloading
        imageViewReference.get().setImageResource(R.drawable.movie_thumb_icon);
    }
    else {
        imageViewReference.get().setImageBitmap(bitmap);
    }            
}

Upvotes: 21

Pramod J George

Reputation: 1723

instead of using the convertview object create a new view each time.

View localView = ((LayoutInflater)parentscreen.getSystemService("layout_inflater")).inflate(R.layout.activity_list_row, null);

By inflating as above.

Upvotes: -2

Gyonder

Reputation: 3756

Views are reused for performance with Adapters. You should use another approch . You have to have a class holder which reuse your views. In your case you class should be something like this:

   public class MoviesAdapter extends ArrayAdapter<ParkCinema> {
    private ArrayList<ParkCinema> movieDataItems;   
    private Activity context;

    public MoviesAdapter(Activity context, int textViewResourceId,       ArrayList<ParkCinema> movieDataItems) {
        super(context, textViewResourceId, movieDataItems);
        this.context = context;
        this.movieDataItems = movieDataItems;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) { 
        if (convertView == null) {
            LayoutInflater vi = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = vi.inflate(R.layout.movie_data_row, null);

                holder = new ViewHolder();

                holder.imageView = (BarImageView) convertView.findViewById(R.id.movie_thumb_icon);
              } else {
                        holder = (ViewHolder) convertView.getTag();

                  }

        ParkCinema movie = movieDataItems.get(position);

        if (movie!=null){

                    String url = movie.poster();

                     if (url!=null) {
                        Bitmap bitmap = fetchBitmapFromCache(url);
                        if (bitmap==null) { 
                            new BitmapDownloaderTask(imageView).execute(url);
                        }
                        else {
                            imageView.setImageBitmap(bitmap);
                        } 
                    } 
        }
        return convertView;
    }

    private LinkedHashMap<String, Bitmap> bitmapCache = new LinkedHashMap<String, Bitmap>();

    private void addBitmapToCache(String url, Bitmap bitmap) {
        if (bitmap != null) {
            synchronized (bitmapCache) {
                bitmapCache.put(url, bitmap);
            }
        }
    }

    private Bitmap fetchBitmapFromCache(String url) {

        synchronized (bitmapCache) {
            final Bitmap bitmap = bitmapCache.get(url);
             if (bitmap != null) {
                return bitmap;
            } 
        }

        return null;


public static class ViewHolder {


        ImageView imageView; 


    }

    }

Upvotes: 0

Images are repeating in ListView

Answers (6)

-Edit-

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