Android 从缓存中读取图片并异步加载的类

最新推荐文章于 2020-05-22 16:58:49 发布

转载最新推荐文章于 2020-05-22 16:58:49 发布 · 738 阅读

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本文介绍了一种用于微博图片异步加载的技术实现方案，通过使用软引用缓存已加载的图片，有效减少了重复加载同一张图片的时间消耗，并提高了应用程序的响应速度。

在新浪微博的微博列表中的图片，为了加速其显示也未了加快程序的响应，可以参考该图片异步加载类实现。

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);
    }
}

在Adapter中使用的方法为：

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;
        }

    }