效果圖

public class ImageLoader {private Handler mUIHandler;private Handler mPollThreadHandler;private Semaphore mSemaphoreThreadPool;private Semaphore mSemaphorePollThreadHandler = new Semaphore(0);//private Thread mPollThread;private HandlerThread mThread;// 輪詢(xún)線(xiàn)程，在后臺(tái)去執(zhí)行下載圖片任務(wù)private ExecutorService mThreadPool;private LinkedList<Runnable> mTaskQueue;private LruCache<String, Bitmap> mLruCache;private static int DEFAULT_THREAD_COUNT = 3;private String mMaxWidth = "mMaxWidth";private String mMaxHeight = "mMaxHeight";private Type mType = Type.LIFO;private enum Type {FIFO, LIFO}private static ImageLoader mInstance;private ImageLoader(int threadCount, Type type) {init(threadCount, type);}public static ImageLoader getInstance() {return getInstance(DEFAULT_THREAD_COUNT, Type.LIFO);}public static ImageLoader getInstance(int threadCount, Type type) {if (mInstance == null) {synchronized (ImageLoader.class) {if (mInstance == null) {mInstance = new ImageLoader(threadCount, type);}}}return mInstance;}private void init(int threadCount, Type type) {mType = type;mSemaphoreThreadPool = new Semaphore(threadCount);mTaskQueue = new LinkedList<Runnable>();mThreadPool = Executors.newFixedThreadPool(threadCount);initBackThread();int maxMemory = (int) Runtime.getRuntime().maxMemory();int cacheMemory = maxMemory / 8;mLruCache = new LruCache<String, Bitmap>(cacheMemory) {@Overrideprotected int sizeOf(String key, Bitmap value) {return value.getRowBytes() * value.getHeight();}};}public void initBackThread(){mThread = new HandlerThread("PollThread");mThread.start();mPollThreadHandler = new Handler(mThread.getLooper()) {@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);mThreadPool.execute(getTask());try {mSemaphoreThreadPool.acquire();} catch (InterruptedException e) {e.printStackTrace();}}};mSemaphorePollThreadHandler.release();/*mPollThread = new Thread() {@Overridepublic void run() {super.run();Looper.prepare();mPollThreadHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);mThreadPool.execute(getTask());try {mSemaphoreThreadPool.acquire();} catch (InterruptedException e) {e.printStackTrace();}}};mSemaphorePollThreadHandler.release();Looper.loop();}};mPollThread.start();*/}private Runnable getTask() {if (mType == Type.FIFO) {return mTaskQueue.removeFirst();} else if (mType == Type.LIFO) {return mTaskQueue.removeLast();}return null;}public void loadImage(final String path, final ImageView imageView) {imageView.setTag(path);if (mUIHandler == null) {mUIHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);ImageHolder holder = (ImageHolder) msg.obj;Bitmap bm = holder.bm;String path = holder.path;ImageView imageView = holder.imageView;if (path.equals(imageView.getTag().toString())) {imageView.setImageBitmap(bm);}}};}Bitmap bm = getBitmapFromLruCache(path);if (bm != null) {refreshImageView(path, bm, imageView);} else {addTask(new Runnable() {@Overridepublic void run() {ImageSize imageSize = getImageViewSize(imageView);Bitmap bm = decodeBitmapFromPath(path, imageSize);addBitmapToLruCache(path, bm);refreshImageView(path, bm, imageView);mSemaphoreThreadPool.release();}});}}private Bitmap decodeBitmapFromPath(String path, ImageSize imageSize) {BitmapFactory.Options options = new BitmapFactory.Options();options.inJustDecodeBounds = true;BitmapFactory.decodeFile(path, options);options.inSampleSize = calculateInSampleSize(options, imageSize.width, imageSize.height);options.inJustDecodeBounds = false;return BitmapFactory.decodeFile(path, options);}private int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {final int height = options.outHeight;final int width = options.outWidth;int inSampleSize = 1;if (height > reqHeight || width > reqWidth) {final int halfHeight = height / 2;final int halfWidth = width / 2;while ((halfHeight / inSampleSize) > reqHeight&& (halfWidth / inSampleSize) > reqWidth) {inSampleSize *= 2;}/* long totalPixels = width * height / inSampleSize;final long totalReqPixelsCap = reqWidth * reqHeight * 2;while (totalPixels > totalReqPixelsCap) {inSampleSize *= 2;totalPixels /= 2;}*/}return inSampleSize;}private ImageSize getImageViewSize(ImageView imageView) {DisplayMetrics metrics = imageView.getContext().getResources().getDisplayMetrics();ViewGroup.LayoutParams lp = imageView.getLayoutParams();int width = imageView.getWidth();if (width <= 0) {width = lp.width;}if (width <= 0) {width = getImageViewFieldValue(imageView, mMaxWidth);}if (width <= 0) {width = metrics.widthPixels;}int height = imageView.getWidth();if (height <= 0) {height = lp.height;}if (height <= 0) {height = getImageViewFieldValue(imageView, mMaxHeight);}if (height <= 0) {height = metrics.heightPixels;}ImageSize imageSize = new ImageSize();imageSize.width = width;imageSize.height = height;return imageSize;}private int getImageViewFieldValue(Object obj, String fieldname) {int value = 0;try {Field field = ImageView.class.getDeclaredField(fieldname);field.setAccessible(true);int fieldvalue = field.getInt(obj);if (fieldvalue > 0 && fieldvalue < Integer.MAX_VALUE) {value = fieldvalue;}} catch (NoSuchFieldException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();}return value;}private synchronized void addTask(Runnable r) {mTaskQueue.add(r);if (mPollThreadHandler == null) {try {mSemaphorePollThreadHandler.acquire();} catch (InterruptedException e) {e.printStackTrace();}}mPollThreadHandler.sendEmptyMessage(0);// 給輪詢(xún)線(xiàn)程發(fā)送消息}private void refreshImageView(String path, Bitmap bm, ImageView imageView) {Message msg = Message.obtain();ImageHolder holder = new ImageHolder();holder.bm = bm;holder.path = path;holder.imageView = imageView;msg.obj = holder;mUIHandler.sendMessage(msg);}private Bitmap getBitmapFromLruCache(String path) {return mLruCache.get(path);}private void addBitmapToLruCache(String path, Bitmap bm) {if (getBitmapFromLruCache(path) == null) {if (bm != null) {mLruCache.put(path, bm);}}}class ImageSize {protected int width;protected int height;}class ImageHolder {protected Bitmap bm;protected String path;protected ImageView imageView;} }

源代碼：https://github.com/JackChan1999/PhotoSelector

參考

• Android 框架練成 教你打造高效的圖片加載框架
• Android Handler 異步消息處理機(jī)制的妙用 創(chuàng)建強(qiáng)大的圖片加載類(lèi)
• Android-仿微信圖片選擇器
• Android照片墻完整版，完美結(jié)合LruCache和DiskLruCache
• 教你寫(xiě)Android ImageLoader框架

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