我有一个ListView，其行可能有或没有图片。当有图片时，我会根据http://developer.android.com/resources/samples/XmlAdapters/src/com/example/android/xmladapters/ImageDownloader.html启动图像加载器。我的一个修改是在动画图像（旋转轮）加载图像时替换所显示的彩色绘图。为了做到这一点，我在构造函数中设置了一个微调器Bitmap，如果要下载的图像不在缓存中，我会在download(String url, ImageView imageView)方法中设置它。我在加载图像并将其设置为ImageView时清除动画。
问题在于动画代码
Animation rotate_picture = AnimationUtils.loadAnimation(context, R.anim.rotate_picture);
imageView.startAnimation(rotate_picture);
在我的ImageDownloader的download方法中，我的适配器变得疯狂，有时会将动画设置为下载的图像，或者将默认图片设置为没有图片的行。
当我评论这两行时，一切正常（除了旋转器当然没有动画）。
有人可以帮忙吗？
适配器的getView
@Override
public View getView(int position, View convertView, final ViewGroup parent) {
View row = convertView;
ItemHolder holder = null;
if(row == null)
{
LayoutInflater inflater = ((Activity)context).getLayoutInflater();
row = inflater.inflate(layoutResourceId, parent, false);
holder = new ItemHolder();
holder.title = (TextView)row.findViewById(R.id.title);
holder.date = (TextView)row.findViewById(R.id.date);
holder.desc = (EllipsizingTextView)row.findViewById(R.id.desc);
holder.pic = (ImageView)row.findViewById(R.id.pic);
row.setTag(holder);
}
else
{
holder = (ItemHolder)row.getTag();
}
Item item = data.get(position);
holder.title.setText(item.title);
holder.date.setText(Utils.UnixTime2String(item.published, "/"));
holder.desc.setMaxLines(3);
holder.desc.setText(item.descriptionintro);
if(item.list_images.size()>0){
holder.pic.setVisibility(View.VISIBLE);
imageLoader.download(GlobalData.BASE_URL + item.list_images.get(0), (ImageView) holder.pic);
}
else{
holder.pic.setVisibility(View.GONE);
holder.pic.setImageResource(0);
}
return row;
}
ImageDownloader
public class ImageDownloader {
private static final String LOG_TAG = "ImageDownloader";
private Integer xbound, ybound;
private static Context context;
private static Bitmap defaultPic;
public ImageDownloader(Context context, Bitmap defaultPic, Integer xbound, Integer ybound){
ImageDownloader.context = context;
ImageDownloader.defaultPic = defaultPic;
this.xbound = xbound;
this.ybound = ybound;
}
/**
* 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) {
//Animation rotate_picture = AnimationUtils.loadAnimation(context, R.anim.rotate_picture);
//imageView.startAnimation(rotate_picture);
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)) {
BitmapDownloaderTask task = new BitmapDownloaderTask(imageView);
DownloadedDrawable downloadedDrawable = new DownloadedDrawable(task);
imageView.setImageDrawable(downloadedDrawable);
task.execute(url);
}
}
/**
* 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;
final HttpClient client = new DefaultHttpClient();
final HttpGet getRequest = new HttpGet(url);
try {
HttpResponse response = client.execute(getRequest);
final int statusCode = response.getStatusLine().getStatusCode();
if (statusCode != HttpStatus.SC_OK) {
return null;
}
final HttpEntity entity = response.getEntity();
if (entity != null) {
InputStream inputStream = null;
try {
inputStream = entity.getContent();
return BitmapFactory.decodeStream(new FlushedInputStream(inputStream), null, null);
} finally {
if (inputStream != null) {
inputStream.close();
}
entity.consumeContent();
}
}
} catch (IOException e) {
getRequest.abort();
} catch (IllegalStateException e) {
getRequest.abort();
} catch (Exception e) {
getRequest.abort();
}
return null;
}
/*
* Cancel and remove download task for a given ImageView. Done when going previous/next to avoid "out of memory" when clicking fast
*/
void cancelDownload(ImageView imageView){
BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView);
if (bitmapDownloaderTask != null) {
bitmapDownloaderTask.cancel(true);
removeBitmapDownloaderTask(imageView);
}
}
private static boolean removeBitmapDownloaderTask(ImageView imageView) {
if (imageView != null) {
Drawable drawable = imageView.getDrawable();
if (drawable instanceof DownloadedDrawable) {
DownloadedDrawable downloadedDrawable = (DownloadedDrawable)drawable;
downloadedDrawable.clearBitmapDownloaderTask();
return true;
}
}
return false;
}
/*
* 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;
}
if(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) {
if(xbound!=null && ybound!=null){
int width = bitmap.getWidth();
int height = bitmap.getHeight();
int xbounding = dpToPx(xbound);
int ybounding = dpToPx(ybound);
// Determine how much to scale: the dimension requiring less scaling is
// closer to the its side. This way the image always stays inside your
// bounding box AND either x/y axis touches it.
float xScale = ((float) xbounding) / width;
float yScale = ((float) ybounding) / height;
float scale = (xScale <= yScale) ? xScale : yScale;
// Create a matrix for the scaling and add the scaling data
Matrix matrix = new Matrix();
matrix.postScale(scale, scale);
// Create a new bitmap and convert it to a format understood by the ImageView
Bitmap scaledBitmap = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix, true);
width = scaledBitmap.getWidth(); // re-use
height = scaledBitmap.getHeight(); // re-use
BitmapDrawable result = new BitmapDrawable(scaledBitmap);
// Apply the scaled bitmap
imageView.setImageDrawable(result);
// Now change ImageView's dimensions to match the scaled image
//LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) imageView.getLayoutParams();
//params.width = width;
//params.height = height;
//imageView.setLayoutParams(params);
}
else{
imageView.clearAnimation();
imageView.setImageBitmap(bitmap);
}
}
}
}
}
}
private int dpToPx(int dp)
{
float density = context.getResources().getDisplayMetrics().density;
return Math.round((float)dp * density);
}
/**
* 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 BitmapDrawable {
private final WeakReference<BitmapDownloaderTask> bitmapDownloaderTaskReference;
public DownloadedDrawable(BitmapDownloaderTask bitmapDownloaderTask) {
super(context.getResources(), defaultPic);
bitmapDownloaderTaskReference =
new WeakReference<BitmapDownloaderTask>(bitmapDownloaderTask);
}
public BitmapDownloaderTask getBitmapDownloaderTask() {
return bitmapDownloaderTaskReference.get();
}
public void clearBitmapDownloaderTask() {
bitmapDownloaderTaskReference.clear();
}
}
/*
*
* Image loaded listener
*
*/
OnImageDownloaderListener onImageDownloaderListener = null;
public interface OnImageDownloaderListener {
public abstract void onImageLoaded(int tag);
}
public void setOnImageDownloaderListener(OnImageDownloaderListener listener) {
onImageDownloaderListener = listener;
}
private void OnImageLoaded(int tag){
if(onImageDownloaderListener!=null) {
onImageDownloaderListener.onImageLoaded(tag);
}
}
/*
* 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 = 20;
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) {
@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.
*/
private 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);
}
}