Android实现从缓存中读取图片与异步加载功能类

public class AsyncImageLoader {
  //SoftReference是软引用，是为了更好的为了系统回收变量
  private HashMap<String, SoftReference<Drawable>> imageCache;
  public AsyncImageLoader() {
    imageCache = new HashMap<String, SoftReference<Drawable>>();
  }
  public Drawable loadDrawable(final String imageUrl,final ImageView imageView, final ImageCallback imageCallback){
    if (imageCache.containsKey(imageUrl)) {
      //从缓存中获取
      SoftReference<Drawable> softReference = imageCache.get(imageUrl);
      Drawable drawable = softReference.get();
      if (drawable != null) {
        return drawable;
      }
    }
    final Handler handler = new Handler() {
      public void handleMessage(Message message) {
        imageCallback.imageLoaded((Drawable) message.obj, imageView,imageUrl);
      }
    };
    //建立新一个新的线程下载图片
    new Thread() {
      @Override
      public void run() {
        Drawable drawable = loadImageFromUrl(imageUrl);
        imageCache.put(imageUrl, new SoftReference<Drawable>(drawable));
        Message message = handler.obtainMessage(0, drawable);
        handler.sendMessage(message);
      }
    }.start();
    return null;
  }
  public static Drawable loadImageFromUrl(String url){
    URL m;
    InputStream i = null;
    try {
      m = new URL(url);
      i = (InputStream) m.getContent();
    } catch (MalformedURLException e1) {
      e1.printStackTrace();
    } catch (IOException e) {
      e.printStackTrace();
    }
    Drawable d = Drawable.createFromStream(i, "src");
    return d;
  }
  //回调接口
  public interface ImageCallback {
    public void imageLoaded(Drawable imageDrawable,ImageView imageView, String imageUrl);
  }
}

public class WeiBoAdapater extends BaseAdapter{
    private AsyncImageLoader asyncImageLoader;
    @Override
    public int getCount() {
      // TODO Auto-generated method stub
      return wbList.size();
    }
    @Override
    public Object getItem(int position) {
      // TODO Auto-generated method stub
      return wbList.get(position);
    }
    @Override
    public long getItemId(int position) {
      // TODO Auto-generated method stub
      return position;
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
      // TODO Auto-generated method stub
      convertView = LayoutInflater.from(getApplicationContext()).inflate(R.layout.weibo, null);
      WeiBoHolder wh = new WeiBoHolder();
      wh.wbicon = (ImageView) convertView.findViewById(R.id.wbicon);
      wh.wbtext = (TextView) convertView.findViewById(R.id.wbtext);
      wh.wbtime = (TextView) convertView.findViewById(R.id.wbtime);
      wh.wbuser = (TextView) convertView.findViewById(R.id.wbuser);
      wh.wbimage=(ImageView) convertView.findViewById(R.id.wbimage);
      WeiBoInfo wb = wbList.get(position);
      if(wb != null)
      {
        convertView.setTag(wb.getId());
        wh.wbuser.setText(wb.getUserName());
        wh.wbtime.setText(wb.getTime());
        wh.wbtext.setText(wb.getText(), TextView.BufferType.SPANNABLE);
        Drawable cachedImage = asyncImageLoader.loadDrawable(wb.getUserIcon(), wh.wbicon, new ImageCallback(){
          public void imageLoaded(Drawable imageDrawable,ImageView imageView,String imageUrl){
            imageView.setImageDrawable(imageDrawable);
          }
        });
        if (cachedImage == null)
        {
          wh.wbicon.setImageResource(R.drawable.usericon);
        }else{
          wh.wbicon.setImageDrawable(cachedImage);
        }
      }
      return convertView;
    }
}