AsyncTask异步加载之图片下载

1.创建图片工具类ImageUtil

public class ImageUtil {
    /*
    *
    * 使用Lru算法来将图片进行缓存，从而节省流量的使用
    *
    * */
    static LruCache<String,Bitmap> cache = new LruCache<String,Bitmap>(5 << 20){
         @Override
         protected int sizeOf(String key, Bitmap value) {
             int size = value.getRowBytes() * value.getHeight();
             return size;
         }
     };
   private static final Executor executor = new ScheduledThreadPoolExecutor(4);

    public static void loadImage(ImageView image,String url){
        Bitmap bitmap = cache.get(url);
        ImageLoader loader = (ImageLoader) image.getTag();//得到当前的标签
        if (loader != null){
            loader.cancel(false);
        }
        if (bitmap != null) {
            image.setImageBitmap(bitmap);
        }else {
            new ImageLoader(image).executeOnExecutor(executor,url);
        }
    }

}

2.创建图片加载器ImageLoader类

public class ImageLoader extends AsyncTask<String,Void,Bitmap> {
    private ImageView image;
    private String url;
    public ImageLoader(ImageView image) {
        this.image = image;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
//        ImageLoader loader = (ImageLoader) image.getTag();
//        if (loader != null) {
//            loader.cancel(false);
//        }
        image.setTag(this);//给当前的异步添加标签，来实现图片在控件的阻塞式加载
        image.setImageResource(R.mipmap.coming);
    }

    @Override
    protected Bitmap doInBackground(String... params) {
        url = params[0];
        try {
            HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
            connection.setRequestMethod("GET");
            connection.setDoInput(true);
            int code = connection.getResponseCode();
            if (code == 200) {
                InputStream is = connection.getInputStream();
//                BitmapFactory.Options options = new BitmapFactory.Options();
//                options.inJustDecodeBounds = true;
//                BitmapFactory.decodeStream(is);
//                options.inSampleSize = 2;
//                options.inJustDecodeBounds = false;
               Bitmap bitmap = BitmapFactory.decodeStream(is);
                return bitmap;
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);

    }

    @Override
    protected void onPostExecute(Bitmap bitmap) {
        super.onPostExecute(bitmap);
        if (bitmap != null) {
            image.setImageBitmap(bitmap);
            ImageUtil.cache.put(url,bitmap);
        }else {
            image.setImageResource(R.mipmap.ic_launcher);
        }
        image.setTag(null);
    }

    @Override
    protected void onCancelled(Bitmap bitmap) {
        if (bitmap != null) {
            ImageUtil.cache.put(url,bitmap);
        }
    }
}