Как я могу указать образ заполнителя?

Я использую ImageDownloader Google, как показано в их многопоточности для статьи блога эффективности: http://android-developers.blogspot.com/2010/07/multithreading-for-performance.html

Я хочу иметь возможность указывать образ заставки по умолчанию, пока изображения загружаются из Интернета. Как я могу это сделать?

Вот код:

/** * This helper class download images from the Internet and binds those with the provided ImageView. * * <p>It requires the INTERNET permission, which should be added to your application's manifest * file.</p> * * A local cache of downloaded images is maintained internally to improve performance. */ public class ImageDownloader { private static final String LOG_TAG = "ImageDownloader"; public enum Mode { NO_ASYNC_TASK, NO_DOWNLOADED_DRAWABLE, CORRECT } private Mode mode = Mode.CORRECT; //Mode.NO_ASYNC_TASK; /** * Download the specified image from the Internet and binds it to the provided ImageView. The * binding is immediate if the image is found in the cache and will be done asynchronously * otherwise. A null bitmap will be associated to the ImageView if an error occurs. * * @param url The URL of the image to download. * @param imageView The ImageView to bind the downloaded image to. */ public void download(String url, ImageView imageView) { resetPurgeTimer(); Bitmap bitmap = getBitmapFromCache(url); if (bitmap == null) { forceDownload(url, imageView); } else { cancelPotentialDownload(url, imageView); imageView.setImageBitmap(bitmap); } } /* * Same as download but the image is always downloaded and the cache is not used. * Kept private at the moment as its interest is not clear. private void forceDownload(String url, ImageView view) { forceDownload(url, view, null); } */ /** * Same as download but the image is always downloaded and the cache is not used. * Kept private at the moment as its interest is not clear. */ private void forceDownload(String url, ImageView imageView) { // State sanity: url is guaranteed to never be null in DownloadedDrawable and cache keys. if (url == null) { imageView.setImageDrawable(null); return; } if (cancelPotentialDownload(url, imageView)) { switch (mode) { case NO_ASYNC_TASK: Bitmap bitmap = downloadBitmap(url); addBitmapToCache(url, bitmap); imageView.setImageBitmap(bitmap); break; case NO_DOWNLOADED_DRAWABLE: imageView.setMinimumHeight(156); BitmapDownloaderTask task = new BitmapDownloaderTask(imageView); task.execute(url); break; case CORRECT: task = new BitmapDownloaderTask(imageView); DownloadedDrawable downloadedDrawable = new DownloadedDrawable(task); imageView.setImageDrawable(downloadedDrawable); imageView.setMinimumHeight(156); task.execute(url); break; } } } /** * Returns true if the current download has been canceled or if there was no download in * progress on this image view. * Returns false if the download in progress deals with the same url. The download is not * stopped in that case. */ private static boolean cancelPotentialDownload(String url, ImageView imageView) { BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView); if (bitmapDownloaderTask != null) { String bitmapUrl = bitmapDownloaderTask.url; if ((bitmapUrl == null) || (!bitmapUrl.equals(url))) { bitmapDownloaderTask.cancel(true); } else { // The same URL is already being downloaded. return false; } } return true; } /** * @param imageView Any imageView * @return Retrieve the currently active download task (if any) associated with this imageView. * null if there is no such task. */ private static BitmapDownloaderTask getBitmapDownloaderTask(ImageView imageView) { if (imageView != null) { Drawable drawable = imageView.getDrawable(); if (drawable instanceof DownloadedDrawable) { DownloadedDrawable downloadedDrawable = (DownloadedDrawable)drawable; return downloadedDrawable.getBitmapDownloaderTask(); } } return null; } Bitmap downloadBitmap(String url) { //final int IO_BUFFER_SIZE = 4 * 1024; // AndroidHttpClient is not allowed to be used from the main thread final HttpClient client = (mode == Mode.NO_ASYNC_TASK) ? new DefaultHttpClient() : AndroidHttpClient.newInstance("Android"); final HttpGet getRequest = new HttpGet(url); try { HttpResponse response = client.execute(getRequest); final int statusCode = response.getStatusLine().getStatusCode(); if (statusCode != HttpStatus.SC_OK) { Log.w("ImageDownloader", "Error " + statusCode + " while retrieving bitmap from " + url); return null; } final HttpEntity entity = response.getEntity(); if (entity != null) { InputStream inputStream = null; try { inputStream = entity.getContent(); // return BitmapFactory.decodeStream(inputStream); // Bug on slow connections, fixed in future release. return BitmapFactory.decodeStream(new FlushedInputStream(inputStream)); } finally { if (inputStream != null) { inputStream.close(); } entity.consumeContent(); } } } catch (IOException e) { getRequest.abort(); Log.w(LOG_TAG, "I/O error while retrieving bitmap from " + url, e); } catch (IllegalStateException e) { getRequest.abort(); Log.w(LOG_TAG, "Incorrect URL: " + url); } catch (Exception e) { getRequest.abort(); Log.w(LOG_TAG, "Error while retrieving bitmap from " + url, e); } finally { if ((client instanceof AndroidHttpClient)) { ((AndroidHttpClient) client).close(); } } return null; } /* * An InputStream that skips the exact number of bytes provided, unless it reaches EOF. */ static class FlushedInputStream extends FilterInputStream { public FlushedInputStream(InputStream inputStream) { super(inputStream); } @Override public long skip(long n) throws IOException { long totalBytesSkipped = 0L; while (totalBytesSkipped < n) { long bytesSkipped = in.skip(n - totalBytesSkipped); if (bytesSkipped == 0L) { int b = read(); if (b < 0) { break; // we reached EOF } else { bytesSkipped = 1; // we read one byte } } totalBytesSkipped += bytesSkipped; } return totalBytesSkipped; } } /** * The actual AsyncTask that will asynchronously download the image. */ class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> { private String url; private final WeakReference<ImageView> imageViewReference; public BitmapDownloaderTask(ImageView imageView) { imageViewReference = new WeakReference<ImageView>(imageView); } /** * Actual download method. */ @Override protected Bitmap doInBackground(String... params) { url = params[0]; return downloadBitmap(url); } /** * Once the image is downloaded, associates it to the imageView */ @Override protected void onPostExecute(Bitmap bitmap) { if (isCancelled()) { bitmap = null; } addBitmapToCache(url, bitmap); if (imageViewReference != null) { ImageView imageView = imageViewReference.get(); BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView); // Change bitmap only if this process is still associated with it // Or if we don't use any bitmap to task association (NO_DOWNLOADED_DRAWABLE mode) if ((this == bitmapDownloaderTask) || (mode != Mode.CORRECT)) { imageView.setImageBitmap(bitmap); } } } } /** * A fake Drawable that will be attached to the imageView while the download is in progress. * * <p>Contains a reference to the actual download task, so that a download task can be stopped * if a new binding is required, and makes sure that only the last started download process can * bind its result, independently of the download finish order.</p> */ static class DownloadedDrawable extends ColorDrawable { private final WeakReference<BitmapDownloaderTask> bitmapDownloaderTaskReference; public DownloadedDrawable(BitmapDownloaderTask bitmapDownloaderTask) { super(Color.BLACK); bitmapDownloaderTaskReference = new WeakReference<BitmapDownloaderTask>(bitmapDownloaderTask); } public BitmapDownloaderTask getBitmapDownloaderTask() { return bitmapDownloaderTaskReference.get(); } } public void setMode(Mode mode) { this.mode = mode; clearCache(); } /* * Cache-related fields and methods. * * We use a hard and a soft cache. A soft reference cache is too aggressively cleared by the * Garbage Collector. */ private static final int HARD_CACHE_CAPACITY = 10; private static final int DELAY_BEFORE_PURGE = 10 * 1000; // in milliseconds // Hard cache, with a fixed maximum capacity and a life duration private final HashMap<String, Bitmap> sHardBitmapCache = new LinkedHashMap<String, Bitmap>(HARD_CACHE_CAPACITY / 2, 0.75f, true) { /** * */ private static final long serialVersionUID = 1L; @Override protected boolean removeEldestEntry(LinkedHashMap.Entry<String, Bitmap> eldest) { if (size() > HARD_CACHE_CAPACITY) { // Entries push-out of hard reference cache are transferred to soft reference cache sSoftBitmapCache.put(eldest.getKey(), new SoftReference<Bitmap>(eldest.getValue())); return true; } else return false; } }; // Soft cache for bitmaps kicked out of hard cache private final static ConcurrentHashMap<String, SoftReference<Bitmap>> sSoftBitmapCache = new ConcurrentHashMap<String, SoftReference<Bitmap>>(HARD_CACHE_CAPACITY / 2); private final Handler purgeHandler = new Handler(); private final Runnable purger = new Runnable() { public void run() { clearCache(); } }; /** * Adds this bitmap to the cache. * @param bitmap The newly downloaded bitmap. */ private void addBitmapToCache(String url, Bitmap bitmap) { if (bitmap != null) { synchronized (sHardBitmapCache) { sHardBitmapCache.put(url, bitmap); } } } /** * @param url The URL of the image that will be retrieved from the cache. * @return The cached bitmap or null if it was not found. */ public Bitmap getBitmapFromCache(String url) { // First try the hard reference cache synchronized (sHardBitmapCache) { final Bitmap bitmap = sHardBitmapCache.get(url); if (bitmap != null) { // Bitmap found in hard cache // Move element to first position, so that it is removed last sHardBitmapCache.remove(url); sHardBitmapCache.put(url, bitmap); return bitmap; } } // Then try the soft reference cache SoftReference<Bitmap> bitmapReference = sSoftBitmapCache.get(url); if (bitmapReference != null) { final Bitmap bitmap = bitmapReference.get(); if (bitmap != null) { // Bitmap found in soft cache return bitmap; } else { // Soft reference has been Garbage Collected sSoftBitmapCache.remove(url); } } return null; } /** * Clears the image cache used internally to improve performance. Note that for memory * efficiency reasons, the cache will automatically be cleared after a certain inactivity delay. */ public void clearCache() { sHardBitmapCache.clear(); sSoftBitmapCache.clear(); } /** * Allow a new delay before the automatic cache clear is done. */ private void resetPurgeTimer() { purgeHandler.removeCallbacks(purger); purgeHandler.postDelayed(purger, DELAY_BEFORE_PURGE); } } 

    Установите ImageView в placeholder в download() перед вызовом forceDownload() .

    Сначала декодируйте растровое изображение, которое вы хотите разместить. Передайте его в DownloadedDrawable, который расширяет BitmapDrawable. Когда я создаю класс, я заполняю mContext допустимым контекстом.

    В силе скачать:

     Bitmap bitmap = BitmapFactory.decodeResource(mContext.getResources(), R.resource.placeholder); imageView.setImageDrawable(new DownloadedDrawable(mContext, handler, bitmap)); 

    Класс downloadDrawable:

     static class DownloadedDrawable extends BitmapDrawable { private final SoftReference<BitmapDownloaderTask> bitmapDownloaderTaskReference; public DownloadedDrawable(Context context, BitmapDownloaderTask bitmapDownloaderTask, Bitmap bitmap) { super(context.getResources(), bitmap ); bitmapDownloaderTaskReference = new SoftReference< BitmapDownloaderTask >(bitmapDownloaderTask); } public BinaryHttpResponseHandler get BitmapDownloaderTask() { return bitmapDownloaderTaskReference.get(); } } 

    Надеюсь, что это поможет:>

    Я не уверен, что полностью понимаю ваш вопрос, но вот какой-то код, который, возможно, поможет вам.

     public class Downloader { private ImageView someImageView; public Downloader() { someImageView = new ImageView(getApplicationContext()); new BitmapDownloaderTask.execute("http://url/to/your/image.jpg") } class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> { @Override protected onPreExecute() { someImageView.setImageBitmap(getResources().getDrawable(R.drawable.placeholder)); } @Override protected Bitmap doInBackground(String... params) { return downloadBitmap(params[0]); } @Override protected void onPostExecute(Bitmap bitmap) { someImageView.setImageBitmap(bitmap); } } }