Android异步加载图片并缓存到内存和SD卡上

* 异步加载图片 * 使用方法： * private AsyncImageLoader asyImg = new AsyncImageLoader(); * asyImg.LoadImage(productItems.get(position).getPic(), (ImageView)view.findViewById(R.id.pic)); */public class AsyncImageLoader {// 为了加快速度，在内存中开启缓存（主要应用于重复图片较多时，或者同一个图片要多次被访问，比如在ListView时来回滚动）public Map<String, SoftReference<Drawable>> imageCache = new HashMap<String, SoftReference<Drawable>>();private ExecutorService executorService = Executors.newFixedThreadPool(5); // 固定五个线程来执行任务private final Handler handler = new Handler();// SD卡上图片储存地址private final String path = Environment.getExternalStorageDirectory().getPath() + "/maiduo";/** *  * @param imageUrl *            图像url地址 * @param callback *            回调接口 * @return 返回内存中缓存的图像，第一次加载返回null */public Drawable loadDrawable(final String imageUrl,final ImageCallback callback) {// 如果缓存过就从缓存中取出数据if (imageCache.containsKey(imageUrl)) {SoftReference<Drawable> softReference = imageCache.get(imageUrl);if (softReference.get() != null) {return softReference.get();}} else if (useTheImage(imageUrl) != null) {return useTheImage(imageUrl);}// 缓存中没有图像，则从网络上取出数据，并将取出的数据缓存到内存中executorService.submit(new Runnable() {public void run() {try {final Drawable drawable = Drawable.createFromStream(new URL(imageUrl).openStream(), "image.png");imageCache.put(imageUrl, new SoftReference<Drawable>(drawable));handler.post(new Runnable() {public void run() {callback.imageLoaded(drawable);}});saveFile(drawable, imageUrl);} catch (Exception e) {throw new RuntimeException(e);}}});return null;}// 从网络上取数据方法public Drawable loadImageFromUrl(String imageUrl) {try {return Drawable.createFromStream(new URL(imageUrl).openStream(),"image.png");} catch (Exception e) {throw new RuntimeException(e);}}// 对外界开放的回调接口public interface ImageCallback {// 注意 此方法是用来设置目标对象的图像资源public void imageLoaded(Drawable imageDrawable);}// 引入线程池，并引入内存缓存功能,并对外部调用封装了接口，简化调用过程public void LoadImage(final String url, final ImageView iv) {if (iv.getImageMatrix() == null) {iv.setImageResource(R.drawable.loading);}// 如果缓存过就会从缓存中取出图像，ImageCallback接口中方法也不会被执行Drawable cacheImage = loadDrawable(url,new AsyncImageLoader.ImageCallback() {// 请参见实现：如果第一次加载url时下面方法会执行public void imageLoaded(Drawable imageDrawable) {iv.setImageDrawable(imageDrawable);}});if (cacheImage != null) {iv.setImageDrawable(cacheImage);}}/** * 保存图片到SD卡上 *  * @param bm * @param fileName *  */public void saveFile(Drawable dw, String url) {try {BitmapDrawable bd = (BitmapDrawable) dw;Bitmap bm = bd.getBitmap();// 获得文件名字final String fileNa = url.substring(url.lastIndexOf("/") + 1,url.length()).toLowerCase();File file = new File(path + "/image/" + fileNa);// 创建图片缓存文件夹boolean sdCardExist = Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED); // 判断sd卡是否存在if (sdCardExist) {File maiduo = new File(path);File ad = new File(path + "/image");// 如果文件夹不存在if (!maiduo.exists()) {// 按照指定的路径创建文件夹maiduo.mkdir();// 如果文件夹不存在} else if (!ad.exists()) {// 按照指定的路径创建文件夹ad.mkdir();}// 检查图片是否存在if (!file.exists()) {file.createNewFile();}}BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(file));bm.compress(Bitmap.CompressFormat.JPEG, 100, bos);bos.flush();bos.close();} catch (Exception e) {// TODO: handle exception}}/** * 使用SD卡上的图片 *  */public Drawable useTheImage(String imageUrl) {Bitmap bmpDefaultPic = null;// 获得文件路径String imageSDCardPath = path+ "/image/"+ imageUrl.substring(imageUrl.lastIndexOf("/") + 1,imageUrl.length()).toLowerCase();File file = new File(imageSDCardPath);// 检查图片是否存在if (!file.exists()) {return null;}bmpDefaultPic = BitmapFactory.decodeFile(imageSDCardPath, null);if (bmpDefaultPic != null || bmpDefaultPic.toString().length() > 3) {Drawable drawable = new BitmapDrawable(bmpDefaultPic);return drawable;} elsereturn null;}}
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