public class Utils {private static final String Util_LOG = makeLogTag(Utils.class);public static String makeLogTag(Class<?> cls) {return cls.getName();}public static void showToast(Context context, String str) {Toast.makeText(context, str, Toast.LENGTH_SHORT).show();}/*** 检查是否存在SD卡* * @return*/public static boolean hasSdcard() {String state = Environment.getExternalStorageState();if (state.equals(Environment.MEDIA_MOUNTED)) {return true;} else {return false;}}/*** 创建目录* * @param context* @param dirName*            文件夹名称* @return*/public static File createFileDir(Context context, String dirName) {String filePath;// 如SD卡已存在，则存储；反之存在data目录下if (hasSdcard()) {// SD卡路径filePath = Environment.getExternalStorageDirectory()+ File.separator + dirName;} else {filePath = context.getCacheDir().getPath() + File.separator+ dirName;}File destDir = new File(filePath);if (!destDir.exists()) {boolean isCreate = destDir.mkdirs();Log.i(Util_LOG, filePath + " has created. " + isCreate);}return destDir;}/*** 删除文件（若为目录，则递归删除子目录和文件）* * @param file* @param delThisPath*            true代表删除参数指定file，false代表保留参数指定file*/public static void delFile(File file, boolean delThisPath) {if (!file.exists()) {return;}if (file.isDirectory()) {File[] subFiles = file.listFiles();if (subFiles != null) {int num = subFiles.length;// 删除子目录和文件for (int i = 0; i < num; i++) {delFile(subFiles[i], true);}}}if (delThisPath) {file.delete();}}/*** 获取文件大小，单位为byte（若为目录，则包括所有子目录和文件）* * @param file* @return*/public static long getFileSize(File file) {long size = 0;if (file.exists()) {if (file.isDirectory()) {File[] subFiles = file.listFiles();if (subFiles != null) {int num = subFiles.length;for (int i = 0; i < num; i++) {size += getFileSize(subFiles[i]);}}} else {size += file.length();}}return size;}/*** 保存Bitmap到指定目录* * @param dir*            目录* @param fileName*            文件名* @param bitmap* @throws IOException*/public static void savaBitmap(File dir, String fileName, Bitmap bitmap) {if (bitmap == null) {return;}File file = new File(dir, fileName);try {file.createNewFile();FileOutputStream fos = new FileOutputStream(file);bitmap.compress(CompressFormat.JPEG, 100, fos);fos.flush();fos.close();} catch (IOException e) {e.printStackTrace();}}/*** 判断某目录下文件是否存在* * @param dir*            目录* @param fileName*            文件名* @return*/public static boolean isFileExists(File dir, String fileName) {return new File(dir, fileName).exists();}
}

public class ImageDownLoader {private static final String ImageDownLoader_Log = Utils.makeLogTag(ImageDownLoader.class);/** 保存正在下载或等待下载的URL和相应失败下载次数（初始为0），防止滚动时多次下载 */private Hashtable<String, Integer> taskCollection;/** 缓存类 */private LruCache<String, Bitmap> lruCache;/** 线程池 */private ExecutorService threadPool;/** 缓存文件目录 （如无SD卡，则data目录下） */private File cacheFileDir;/** 缓存文件夹 */private static final String DIR_CACHE = "cache";/** 缓存文件夹最大容量限制（10M） */private static final long DIR_CACHE_LIMIT = 10 * 1024 * 1024;/** 图片下载失败重试次数 */private static final int IMAGE_DOWNLOAD_FAIL_TIMES = 2;public ImageDownLoader(Context context) {// 获取系统分配给每个应用程序的最大内存int maxMemory = (int) Runtime.getRuntime().maxMemory();// 给LruCache分配最大内存的1/8lruCache = new LruCache<String, Bitmap>(maxMemory / 8) {// 必须重写此方法，来测量Bitmap的大小@Overrideprotected int sizeOf(String key, Bitmap value) {return value.getRowBytes() * value.getHeight() / 1024;}};taskCollection = new Hashtable<String, Integer>();// 创建线程数threadPool = Executors.newFixedThreadPool(10);cacheFileDir = Utils.createFileDir(context, DIR_CACHE);}/*** 添加Bitmap到内存缓存* * @param key* @param bitmap*/private void addLruCache(String key, Bitmap bitmap) {if (getBitmapFromMemCache(key) == null && bitmap != null) {lruCache.put(key, bitmap);}}/*** 从内存缓存中获取Bitmap* * @param key* @return*/private Bitmap getBitmapFromMemCache(String key) {return lruCache.get(key);}/*** 异步下载图片，并按指定宽度和高度压缩图片* * @param url* @param width* @param height* @param listener*            图片下载完成后调用接口*/public void loadImage(final String url, final int width, final int height,AsyncImageLoaderListener listener) {Log.i(ImageDownLoader_Log, "download:" + url);final ImageHandler handler = new ImageHandler(listener);Runnable runnable = new Runnable() {@Overridepublic void run() {Bitmap bitmap = downloadImage(url, width, height);Message msg = handler.obtainMessage();msg.obj = bitmap;handler.sendMessage(msg);// 将Bitmap 加入内存缓存addLruCache(url, bitmap);// 加入文件缓存前，需判断缓存目录大小是否超过限制，超过则清空缓存再加入long cacheFileSize = Utils.getFileSize(cacheFileDir);if (cacheFileSize > DIR_CACHE_LIMIT) {Log.i(ImageDownLoader_Log, cacheFileDir+ " size has exceed limit." + cacheFileSize);Utils.delFile(cacheFileDir, false);taskCollection.clear();}// 缓存文件名称（ 替换url中非字母和非数字的字符，防止系统误认为文件路径）String urlKey = url.replaceAll("[^\\w]", "");// 将Bitmap加入文件缓存Utils.savaBitmap(cacheFileDir, urlKey, bitmap);}};// 记录该url，防止滚动时多次下载，0代表该url下载失败次数taskCollection.put(url, 0);threadPool.execute(runnable);}/*** 获取Bitmap, 若内存缓存为空，则去文件缓存中获取* * @param url* @return 若缓存中没找到，则返回null*/public Bitmap getBitmapCache(String url) {// 去处url中特殊字符作为文件缓存的名称String urlKey = url.replaceAll("[^\\w]", "");if (getBitmapFromMemCache(url) != null) {return getBitmapFromMemCache(url);} else if (Utils.isFileExists(cacheFileDir, urlKey)&& Utils.getFileSize(new File(cacheFileDir, urlKey)) > 0) {// 从文件缓存中获取BitmapBitmap bitmap = BitmapFactory.decodeFile(cacheFileDir.getPath()+ File.separator + urlKey);// 将Bitmap 加入内存缓存addLruCache(url, bitmap);return bitmap;}return null;}/*** 下载图片，并按指定高度和宽度压缩* * @param url* @param width* @param height* @return*/private Bitmap downloadImage(String url, int width, int height) {Bitmap bitmap = null;HttpClient httpClient = new DefaultHttpClient();try {httpClient.getParams().setParameter(CoreProtocolPNames.PROTOCOL_VERSION, HttpVersion.HTTP_1_1);HttpPost httpPost = new HttpPost(url);HttpResponse httpResponse = httpClient.execute(httpPost);if (httpResponse.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {HttpEntity entity = httpResponse.getEntity();//解决缩放大图时出现SkImageDecoder::Factory returned null错误byte[] byteIn = EntityUtils.toByteArray(entity);BitmapFactory.Options bmpFactoryOptions = new BitmapFactory.Options();bmpFactoryOptions.inJustDecodeBounds = true;BitmapFactory.decodeByteArray(byteIn, 0, byteIn.length,bmpFactoryOptions);int heightRatio = (int) Math.ceil(bmpFactoryOptions.outHeight/ height);int widthRatio = (int) Math.ceil(bmpFactoryOptions.outWidth/ width);if (heightRatio > 1 && widthRatio > 1) {bmpFactoryOptions.inSampleSize = heightRatio > widthRatio ? heightRatio: widthRatio;}bmpFactoryOptions.inJustDecodeBounds = false;bitmap = BitmapFactory.decodeByteArray(byteIn, 0,byteIn.length, bmpFactoryOptions);}} catch (ClientProtocolException e) {e.printStackTrace();} catch (ConnectTimeoutException e) {e.printStackTrace();} catch (Exception e) {e.printStackTrace();} finally {if (httpClient != null && httpClient.getConnectionManager() != null) {httpClient.getConnectionManager().shutdown();}}// 下载失败，再重新下载// 本例是图片下载失败则再次下载，可根据需要改变，比如记录下载失败的图片URL，在某个时刻再次下载if (taskCollection.get(url) != null) {int times = taskCollection.get(url);if (bitmap == null&& times < IMAGE_DOWNLOAD_FAIL_TIMES) {times++;taskCollection.put(url, times);bitmap = downloadImage(url, width, height);Log.i(ImageDownLoader_Log, "Re-download " + url + ":" + times);}}return bitmap;}/*** 取消正在下载的任务*/public synchronized void cancelTasks() {if (threadPool != null) {threadPool.shutdownNow();threadPool = null;}}/*** 获取任务列表* * @return*/public Hashtable<String, Integer> getTaskCollection() {return taskCollection;}/** 异步加载图片接口 */public interface AsyncImageLoaderListener {void onImageLoader(Bitmap bitmap);}/** 异步加载完成后，图片处理 */static class ImageHandler extends Handler {private AsyncImageLoaderListener listener;public ImageHandler(AsyncImageLoaderListener listener) {this.listener = listener;}@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);listener.onImageLoader((Bitmap) msg.obj);}}
}

public class ImageGridViewAdapter extends BaseAdapter implements OnScrollListener {/** 数据源 */private List<String> data;/** 图片下载类 */private ImageDownLoader loader;/** 判定是否第一次加载 */private boolean isFirstEnter = true;/** 第一张可见Item下标 */private int firstVisibleItem;/** 每屏Item可见数 */private int visibleItemCount;/** GridView实例 */private GridView gridView;private Context context;public ImageGridViewAdapter(Context context, GridView gridView, List<String> data) {this.context = context;this.gridView = gridView;this.data = data;loader = new ImageDownLoader(context);this.gridView.setOnScrollListener(this);}@Overridepublic int getCount() {return data.size();}@Overridepublic Object getItem(int position) {return data.get(position);}@Overridepublic long getItemId(int position) {return position;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {String url = data.get(position);if (convertView == null) {convertView = LayoutInflater.from(context).inflate(R.layout.photo_item, null);}ImageView imageView = (ImageView) convertView.findViewById(R.id.photo);// 设置Tag，保证异步加载图片不乱序imageView.setTag(url);setImageView(imageView, url);return convertView;}private void setImageView(ImageView imageView, String url) {Bitmap bitmap = loader.getBitmapCache(url);if (bitmap != null) {imageView.setImageBitmap(bitmap);} else {imageView.setImageResource(R.drawable.empty_photo);}}@Overridepublic void onScrollStateChanged(AbsListView view, int scrollState) {// 当停止滚动时，加载图片if (scrollState == SCROLL_STATE_IDLE) {loadImage(firstVisibleItem, visibleItemCount);}}@Overridepublic void onScroll(AbsListView view, int firstVisibleItem,int visibleItemCount, int totalItemCount) {this.firstVisibleItem = firstVisibleItem;this.visibleItemCount = visibleItemCount;if (isFirstEnter && visibleItemCount > 0) {loadImage(firstVisibleItem, visibleItemCount);isFirstEnter = false;}}/*** 加载图片，若缓存中没有，则根据url下载* * @param firstVisibleItem* @param visibleItemCount*/private void loadImage(int firstVisibleItem, int visibleItemCount) {Bitmap bitmap = null;for (int i = firstVisibleItem; i < firstVisibleItem + visibleItemCount; i++) {String url = data.get(i);final ImageView imageView = (ImageView) gridView.findViewWithTag(url);bitmap = loader.getBitmapCache(url);if (bitmap != null) {imageView.setImageBitmap(bitmap);} else {// 防止滚动时多次下载if (loader.getTaskCollection().containsKey(url)) {continue;}imageView.setImageDrawable(context.getResources().getDrawable(R.drawable.empty_photo));loader.loadImage(url, imageView.getWidth(),imageView.getHeight(),new ImageDownLoader.AsyncImageLoaderListener() {@Overridepublic void onImageLoader(Bitmap bitmap) {if (imageView != null && bitmap != null) {imageView.setImageBitmap(bitmap);}}});}}}/*** 取消下载任务*/public void cancelTasks() {loader.cancelTasks();}
}

<uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" /> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />