public View getView(int position, View convertView, ViewGroup parent) {ViewHolder holder = null;if (convertView == null) {holder = new ViewHolder();convertView = LayoutInflater.from(context).inflate(R.layout.list_item, null);holder.img = (ImageView) convertView.findViewById(R.id.userimage);convertView.setTag(holder);} else {holder = (ViewHolder) convertView.getTag();}User user = list.get(position);// 给 ImageView 设置一个 tagholder.img.setTag(user.getImgUrl());// 预设一个图片holder.img.setImageResource(R.drawable.ic_launcher);final String tmpImageUrl = user.getImgUrl();if (user.getImgUrl() != null && !user.getImgUrl().equals("")) {Bitmap bitmap = imageLoader.loadImage(holder.img, user.getImgUrl(),new ImageDownloadCallBack() {@Overridepublic void onImageDownloaded(ImageView imageView,Bitmap bitmap) {// 通过 tag 来防止图片错位if (imageView.getTag() != null&& imageView.getTag().equals(tmpImageUrl)) {imageView.setImageBitmap(bitmap);}}});if (bitmap != null) {holder.img.setImageBitmap(bitmap);}}return convertView;
}

/*** 图片异步加载类* * @author Leslie.Fang* @company EnwaySoft* */
public class AsyncImageLoader {// 最大线程数private static final int MAX_THREAD_NUM = 10;private Map<String, SoftReference<Bitmap>> imageCaches = null;private FileUtil fileUtil;// 线程池private ExecutorService threadPools = null;public AsyncImageLoader(Context context) {imageCaches = new HashMap<String, SoftReference<Bitmap>>();fileUtil = new FileUtil(context);}public Bitmap loadImage(final ImageView imageView, final String imageUrl,final ImageDownloadCallBack imageDownloadCallBack) {final String filename = imageUrl.substring(imageUrl.lastIndexOf("/") + 1);final String filepath = fileUtil.getAbsolutePath() + "/" + filename;// 先从软引用中找if (imageCaches.containsKey(imageUrl)) {SoftReference<Bitmap> reference = imageCaches.get(imageUrl);Bitmap bitmap = reference.get();// 软引用中的 Bitmap 对象可能随时被回收// 如果软引用中的 Bitmap 已被回收，则从文件中找if (bitmap != null) {Log.i("aaaa", "cache exists " + filename);return bitmap;}}// 从文件中找if (fileUtil.isBitmapExists(filename)) {Log.i("aaaa", "file exists " + filename);Bitmap bitmap = BitmapFactory.decodeFile(filepath);// 重新加入到内存软引用中imageCaches.put(imageUrl, new SoftReference<Bitmap>(bitmap));return bitmap;}// 软引用和文件中都没有再从网络下载if (imageUrl != null && !imageUrl.equals("")) {if (threadPools == null) {threadPools = Executors.newFixedThreadPool(MAX_THREAD_NUM);}final Handler handler = new Handler() {@Overridepublic void handleMessage(Message msg) {if (msg.what == 111 && imageDownloadCallBack != null) {Bitmap bitmap = (Bitmap) msg.obj;imageDownloadCallBack.onImageDownloaded(imageView,bitmap);}}};Thread thread = new Thread() {@Overridepublic void run() {Log.i("aaaa", Thread.currentThread().getName()+ " is running");InputStream inputStream = HTTPService.getInstance().getStream(imageUrl);Bitmap bitmap = BitmapFactory.decodeStream(inputStream);// 图片下载成功重新缓存并执行回调刷新界面if (bitmap != null) {// 加入到软引用中imageCaches.put(imageUrl, new SoftReference<Bitmap>(bitmap));// 缓存到文件系统fileUtil.saveBitmap(filepath, bitmap);Message msg = new Message();msg.what = 111;msg.obj = bitmap;handler.sendMessage(msg);}}};threadPools.execute(thread);}return null;}public void shutDownThreadPool() {if (threadPools != null) {threadPools.shutdown();threadPools = null;}}/*** 图片下载完成回调接口* */public interface ImageDownloadCallBack {void onImageDownloaded(ImageView imageView, Bitmap bitmap);}
}