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我有一個擴展ArrayAdapter的自定義適配器，它實現了視圖持有者模式以顯示來自Web服務的數據（文本+圖像）。Android：當向ArrayAdapter添加數據時可見的ListView圖像閃爍
爲我用的是異步任務模式從Android的開發者網站上的先進的訓練圖像的延遲加載，
我也使用磁盤+ RAM位圖緩存。
當有額外的數據要檢索我添加一個頁腳視圖，點擊它從Web服務檢索額外的數據並將其添加到適配器。
問題是，當這個新數據被添加時，一些可見圖像正在改變並立即改變回來，這導致奇怪的閃爍。
除此之外，一切工作正常，滾動平穩。
據我所知，當添加新數據時刷新可見視圖時，會發生這些圖像更改。
有沒有辦法繞過這種不需要的行爲？
這是階級做下載和管理異步任務
public class ImageDownloader {
private ImageCache mCache;
private int reqWidth;
private int reqHeight;
public void download(String url, ImageView imageView, ImageCache imageCache, int reqHeight, int reqWidth) {
mCache = imageCache;
this.reqHeight = reqHeight;
this.reqWidth = reqWidth;
if (cancelPotentialDownload(url, imageView)) {
BitmapDownloaderTask task = new BitmapDownloaderTask(imageView);
DownloadedDrawable downloadedDrawable = new DownloadedDrawable(task);
imageView.setImageDrawable(downloadedDrawable);
task.execute(url);
}
}
private class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> {
private String url;
private WeakReference<ImageView> imageViewReference;
public BitmapDownloaderTask(ImageView imageView) {
imageViewReference = new WeakReference<ImageView>(imageView);
}
@Override
protected Bitmap doInBackground(String... strings) {
Bitmap bitmap = null;
try {
bitmap = mCache.getBitmapFromURL(strings[0], reqWidth, reqHeight);
} catch (IOException e) {
}
return bitmap;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
if (isCancelled()) bitmap = null;
if (imageViewReference != null) {
ImageView imageView = imageViewReference.get();
BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView);
if (imageView != null) {
imageView.setImageBitmap(bitmap);
}
}
}
}
private static class DownloadedDrawable extends ColorDrawable {
private WeakReference<BitmapDownloaderTask> bitmapDownloaderTaskReference;
public DownloadedDrawable(BitmapDownloaderTask bitmapDownloaderTask) {
bitmapDownloaderTaskReference = new WeakReference<BitmapDownloaderTask>(bitmapDownloaderTask);
}
public BitmapDownloaderTask getBitmapDownloaderTask() {
return bitmapDownloaderTaskReference.get();
}
}
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;
}
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 {
return false;
}
}
return true;
}
}
這是適配器：
私有類PlaceAdapter擴展ArrayAdapter { 最終詮釋viewResourceId;
public PlaceAdapter(Context context, int textViewResourceId, List<PlaceModel> objects) {
super(context, textViewResourceId, objects);
viewResourceId = textViewResourceId;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
LayoutInflater inflater = getLayoutInflater();
convertView = inflater.inflate(viewResourceId, null);
holder = new ViewHolder(convertView);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
PlaceModel place = getItem(position);
holder.name.setText(place.getName());
holder.address.setText(place.getVicinity());
holder.position = position;
if (place.getIcon() != null) {
String url = mImageViewUrls.get(holder.image);
if (url == null || (url != null && !url.equals(place.getIcon()))) {
mDownloader.download(place.getIcon(), holder.image, mCache, 100, 100);
mImageViewUrls.put(holder.image, place.getIcon());
}
} else {
holder.image.setImageBitmap(null);
mImageViewUrls.remove(holder.image);
}
return convertView;
}
}
private class ViewHolder {
public final ImageView image;
public final TextView name;
public final TextView address;
public int position;
public ViewHolder(View row) {
image = (ImageView) row.findViewById(R.id.placeRow_imageView);
name = (TextView) row.findViewById(R.id.placeRow_placeName);
address = (TextView) row.findViewById(R.id.placeRow_placeAddress);
}
}
mImageViewUrls是WeakHashMap<ImageView, String>，一個ImageView和URL之間映射，可以通過檢查被減小，從而冗餘異步任務調用如果ImageView已經顯示所需要的圖像。沒有這個實現，數據變化的所有可見圖像都會發生閃爍。有了這個，它只發生在一些圖像上。
編輯：我試圖消除這個問題的可能原因，首先我試圖完全繞過緩存實施，並從網絡下載每個位圖，然後我試圖用CommonsWare的無盡的適配器包裝我的適配器，並與我得到了相同結果..所以這隻留下了ImageDownloader類和我的適配器儘可能的原因..我完全失去了這一點。