Android实现ListView异步加载的方法(改进版)

@Override
   public View getView(int position, View convertView, ViewGroup parent) {
         …………
     ViewHolder VH = null;
         …………
      VH.mImageView.setTag(position);
      VH.mThumb.setImageDrawable(imageLoader.loadDrawable(position,
        new ImageCallback() {
          public void imageLoaded(Drawable imageDrawable, int position) {
            ImageView imageViewByTag = (ImageView) mList.findViewWithTag(position);
            if (imageViewByTag != null) {
              imageViewByTag.setImageDrawable(imageDrawable);
              }
            }
         }));
  }
  private static LruCache<Long, Drawable> mCache = new LruCache<Long, Drawable>(100);
  public class AsyncImageLoader {
    public Drawable loadDrawable(final int position, final ImageCallback callback){
      Drawable d = null;
      d = mCache.get(position);
      if (d == null) {
        final Handler handler=new Handler(){
          @Override
          public void handleMessage(Message msg) {
            callback.imageLoaded((Drawable) msg.obj, position);
          }
        };
        Thread t = new Thread(){
          public void run() {
            Drawable drawable = Utils.getDrawable(mContext, position, 1, mMyDefaultIcon);
            Drawable value = mCache.get(position);//cache有可能已经被更改了，所以重新取一次
            if (value == null) {
              mCache.put(position, drawable);
            } else {
              drawable = value;
            }
            handler.sendMessage(handler.obtainMessage(0,drawable));
          };
        };
        t.setPriority(Thread.MIN_PRIORITY);
        t.start();
        return mMyDefaultIcon;
      } else {
        return d;
      }
    }
  }
  public interface ImageCallback{
    public void imageLoaded(Drawable imageDrawable, int position);
  }