Android基础篇异步获取网络图片

很多时候，我们从网络上获取到的图片只是一个Url地址。

我们必须采用异步加载的方法，将图片显示才来。

public class AsyncImageLoader {

     private HashMap<String, SoftReference<Drawable>> imageCache;
      
         public AsyncImageLoader() {
             imageCache = new HashMap<String, SoftReference<Drawable>>();
         }
      
         public Drawable loadDrawable(final String imageUrl, final ImageCallback imageCallback) {
             if (imageCache.containsKey(imageUrl)) {
                 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, imageUrl);
                 }
             };
             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;
        }
      
         public interface ImageCallback {
             public void imageLoaded(Drawable imageDrawable, String imageUrl);
         }

}

当我们需要使用的时候

        viewHolder.mWeiboPhoto.setTag(mFriendBeans.get(position).getPhoto());
        Drawable cachedImage = asyncImage.loadDrawable(mFriendBeans.get(position).getPhoto(), new ImageCallback() {
            public void imageLoaded(Drawable imageDrawable, String imageUrl) {
                ImageView imageViewByTag = (ImageView) mListView.findViewWithTag(imageUrl);
                if (imageViewByTag != null) {
                    imageViewByTag.setImageDrawable(imageDrawable);
                }
            }
        });
        if (cachedImage == null) {
            Log.info("json", "json is null");
            viewHolder.mWeiboPhoto.setImageResource(R.drawable.sinaweibo);
        }else{
            Log.info("json", "json is not null");
            viewHolder.mWeiboPhoto.setImageDrawable(cachedImage);//图标
        }