Android列表视图更新

Question

I am struggling to update a list view with data from a database, this works nicely by using a SimpleCursorAdapter. But the image view on the rows is not updated on the activity start, I have to scroll through the list a few times and only then the images are loaded in the image view.

This is the binder i am using for the SimpleCursorAdapter:

 private class PromotionViewBinder implements SimpleCursorAdapter.ViewBinder {
            private int done;
            public boolean setViewValue(View view, Cursor cursor, int index) {
                Log.e(""+cursor.getCount(),"");
                View tmpview = view;

                 if (index == cursor.getColumnIndex(PromotionsTable.SEEN_COL)) {
                     boolean read = cursor.getInt(index) > 0 ? true : false;
                     TextView title = (TextView) tmpview;
                     if (!read) {
                         title.setTypeface(Typeface.DEFAULT_BOLD, 0);
                     } else {
                         title.setTypeface(Typeface.DEFAULT);
                     }
                     return true;
                 }  else if (tmpview.getId() == R.id.promotions_list_row_image){
                        String imageURL = cursor.getString(index);
                        Log.e("",imageURL);
                        imageRetriever.displayImage(imageURL, (ImageView)tmpview);
                        return true;
                } else {
                     return false;
                 }
             }
         }

The image retriever class is the LazyList example from here . As you will see this is using a runnable to retrieve the images and once the task is done is automatically updating the given imageView...Do you think that the reference to the imageView is lost somewhere on the way?

Thanx in advance, Nick

package com.tipgain.promotions;

The image retriever class:

/**
 * This class is used for retrieving images from a given web link. it uses local
 * storage and memory to store the images. Once a image is downloaded
 * successfully the UI gets updated automatically.
 * 
 * 
 */
public class ImageRetriever {
    private final String TAG = ImageRetriever.class.getName();

    private MemoryImageCache memoryImgCache = new MemoryImageCache();
    private LocalStorageImageCache localFileCache;
    private Map<ImageView, String> imageViewHolders = Collections
            .synchronizedMap(new WeakHashMap<ImageView, String>());
    private ExecutorService execService;
    final int defaultImageID = R.drawable.photo_not_available;

    public ImageRetriever(Context context) {
        localFileCache = new LocalStorageImageCache(context);
        execService = Executors.newFixedThreadPool(5);
    }

    public void displayImage(String url, ImageView imageView) {
        imageViewHolders.put(imageView, url);
        Bitmap bmp = memoryImgCache.retrieve(url);

        if (bmp != null) {
            Log.e("case 1", " " + (bmp != null));
            imageView.setImageBitmap(bmp);

        } else {
            Log.e("case 2", " " + (bmp == null));
            addImageToQueue(url, imageView);
            imageView.setImageResource(defaultImageID);
        }
    }

    private void addImageToQueue(String url, ImageView imageView) {
        NextImageToLoad img = new NextImageToLoad(url, imageView);
        execService.submit(new ImagesRetriever(img));
    }

    /**
     * This method is used for retrieving the Bitmap Image.
     * 
     * @param url
     *            String representing the url pointing to the image.
     * @return Bitmap representing the image
     */
    private Bitmap getBitmap(String url) {
        File imageFile = localFileCache.getFile(url);

        // trying to get the bitmap from the local storage first
        Bitmap bmp = decodeImageFile(imageFile);
        if (bmp != null)
            return bmp;

        // if the file was not found locally we retrieve it from the web
        try {
            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(imageFile);
            Utils.CopyStream(is, os);
            os.close();
            bmp = decodeImageFile(imageFile);
            return bmp;
        } catch (MalformedURLException e) {
            Log.e(TAG, e.getMessage());
        } catch (FileNotFoundException e) {
            Log.e(TAG, e.getMessage());
        } catch (IOException e) {
            Log.e(TAG, e.getMessage());
        }
        return null;
    }

    /**
     * This method is used for decoding a given image file. Also, to reduce
     * memory, the image is also scaled.
     * 
     * @param imageFile
     * @return
     */
    private Bitmap decodeImageFile(File imageFile) {
        try {
            BitmapFactory.Options options = new BitmapFactory.Options();
            options.inJustDecodeBounds = true;
            BitmapFactory.decodeStream(new FileInputStream(imageFile), null,
                    options);

            // Find the correct scale value. It should be the power of 2.
            // Deciding the perfect scaling value. (^2).
            final int REQUIRED_SIZE = 100;
            int tmpWidth = options.outWidth, tmpHeight = options.outHeight;
            int scale = 1;
            while (true) {
                if (tmpWidth / 2 < REQUIRED_SIZE
                        || tmpHeight / 2 < REQUIRED_SIZE)
                    break;
                tmpWidth /= 2;
                tmpHeight /= 2;
                scale *= 2;
            }

            // decoding using inSampleSize
            BitmapFactory.Options option2 = new BitmapFactory.Options();
            option2.inSampleSize = scale;
            return BitmapFactory.decodeStream(new FileInputStream(imageFile),
                    null, option2);
        } catch (FileNotFoundException e) {
            Log.e(TAG, e.getLocalizedMessage());
        }
        return null;
    }

    private boolean reusedImage(NextImageToLoad image) {
        Context c = image.imageView.getContext();
        c.getContentResolver().notifyChange(PromotionsProvider.CONTENT_URI, null);

        String tag = imageViewHolders.get(image.imageView);
        if ((tag == null) || (!tag.equals(image.url)))
            return true;
        return false;
    }

    /**
     * Clears the Memory and Local cache
     */
    public void clearCache() {
        memoryImgCache.clear();
        localFileCache.clear();
    }

    /**
     * This class implements a runnable that is used for updating the promotions
     * images on the UI
     * 
     * 
     */
    class UIupdater implements Runnable {
        Bitmap bmp;
        NextImageToLoad image;

        public UIupdater(Bitmap bmp, NextImageToLoad image) {
            this.bmp = bmp;
            this.image = image;
            Log.e("", "ui updater");
        }

        public void run() {
            Log.e("ui updater", "ui updater");
            if (reusedImage(image))
                return;
            Log.e("nick", "" + (bmp == null) + "     chberugv");
            if (bmp != null){
                image.imageView.setImageBitmap(bmp);
                Context c = image.imageView.getContext();
                c.getContentResolver().notifyChange(PromotionsProvider.CONTENT_URI, null);

            }else
                image.imageView.setImageResource(defaultImageID);

            }
    }

    private class ImagesRetriever implements Runnable {
        NextImageToLoad image;

        ImagesRetriever(NextImageToLoad image) {
            this.image = image;
        }

        public void run() {
            Log.e("images retirever", " images retriever");
            if (reusedImage(image))
                return;
            Bitmap bmp = getBitmap(image.url);
            memoryImgCache.insert(image.url, bmp);
            if (reusedImage(image))
                return;
            UIupdater uiUpdater = new UIupdater(bmp, image);
            Activity activity = (Activity) image.imageView.getContext();
            activity.runOnUiThread(uiUpdater);
            //Context c = image.imageView.getContext();
            //c.getContentResolver().notifyChange(PromotionsProvider.CONTENT_URI, null);


        }
    }

    /**
     * This class encapsulates the image being downloaded.
     * 
     * @author Nicolae Anca
     * 
     */
    private class NextImageToLoad {
        public String url;
        public ImageView imageView;

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

}

Modified Runnable:

class UIupdater implements Runnable {
    Bitmap bmp;
    NextImageToLoad image;

    public UIupdater(Bitmap bmp, NextImageToLoad image) {
        this.bmp = bmp;
        this.image = image;
    }

    public void run() {
        if (reusedImage(image))
            return;
        if (bmp != null){
            image.imageView.setImageBitmap(bmp);
            Context c = image.imageView.getContext();
            c.getContentResolver().notifyChange(PromotionsProvider.CONTENT_URI, null);

        }else
            image.imageView.setImageResource(defaultImageID);

        }
}

Answer 1

Thats an interesting way to do what you are doing. Have you tried extending the Simple Cursor Adapter?

1. What you do is implement a ViewHolder and put your imageview in it.

2. Then in your ImageRetriever, write a Listener which will be called once the image is ready and retrieved.

3. Implement this listener in the Viewholder.

4. You create the view in getView() and request for the image in BindView().

5. Once the image gets loaded, the list will be refreshed automatically.

Answer 2

one way to do it is by calling notifyDataSetChenged on listview, and another was is to have adapter as member variable and when something changes on listview you call a function that assigns new listadapter to member adapter. That way your list will be redraw on change.

Answer 3

我想，您必须使用一些处理程序，在图像加载后调用，这将为列表适配器调用notifyDataSetChanged