Android编程图片加载类ImageLoader定义与用法实例分析
本文实例讲述了Android编程图片加载类ImageLoader定义与用法。分享给大家供大家参考,具体如下:
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解析:
1)图片加载使用单例模式,避免多次调用时产生死锁
2)核心对象 LruCache
图片加载时先判断缓存里是否有图片,如果有,就使用缓存里的
没有就加载网络的,然后置入缓存
3)使用了线程池ExecutorService mThreadPool技术
4)使用了Semaphore 信号来控制变量按照先后顺序执行,避免空指针的问题
如何使用:
在Adapter里加载图片时
复制代码 代码如下:
ImageLoader.getInstance.loadImage("/upload/otherpic63/125059.jpg", mImageView, true);
源码:
/** * @描述 图片加载类 * @项目名称 App_News * @包名 com.android.news.tools * @类名 ImageLoader * @author chenlin * @date 2015-3-7 下午7:35:28 * @version 1.0 */ public class ImageLoader { private static ImageLoader mInstance; /** * 图片缓存的核心对象 */ private LruCachemLruCache; /** * 线程池 */ private ExecutorService mThreadPool; private static final int DEAFULT_THREAD_COUNT = 1; /** * 队列的调度方式 */ private Type mType = Type.LIFO; /** * 任务队列 */ private LinkedList mTaskQueue; /** * 后台轮询线程 */ private Thread mPoolThread; private Handler mPoolThreadHandler; /** * UI线程中的Handler */ private Handler mUIHandler; private Semaphore mSemaphorePoolThreadHandler = new Semaphore(0); private Semaphore mSemaphoreThreadPool; private boolean isDiskCacheEnable = true; private static final String TAG = "ImageLoader"; public enum Type { FIFO, LIFO; } private ImageLoader(int threadCount, Type type) { init(threadCount, type); } /** * 初始化 * * @param threadCount * @param type */ private void init(int threadCount, Type type) { initBackThread(); // 获取我们应用的最大可用内存 int maxMemory = (int) Runtime.getRuntime().maxMemory(); int cacheMemory = maxMemory / 8; mLruCache = new LruCache (cacheMemory) { @Override protected int sizeOf(String key, Bitmap value) { return value.getRowBytes() * value.getHeight(); } }; // 创建线程池 mThreadPool = Executors.newFixedThreadPool(threadCount); mTaskQueue = new LinkedList (); mType = type; mSemaphoreThreadPool = new Semaphore(threadCount); } /** * 初始化后台轮询线程 */ private void initBackThread() { // 后台轮询线程 mPoolThread = new Thread() { @Override public void run() { Looper.prepare(); mPoolThreadHandler = new Handler() { @Override public void handleMessage(Message msg) { // 线程池去取出一个任务进行执行 mThreadPool.execute(getTask()); try { mSemaphoreThreadPool.acquire(); } catch (InterruptedException e) { } } }; // 释放一个信号量 mSemaphorePoolThreadHandler.release(); Looper.loop(); }; }; mPoolThread.start(); } public static ImageLoader getInstance() { if (mInstance == null) { synchronized (ImageLoader.class) { if (mInstance == null) { mInstance = new ImageLoader(DEAFULT_THREAD_COUNT, Type.LIFO); } } } return mInstance; } public static ImageLoader getInstance(int threadCount, Type type) { if (mInstance == null) { synchronized (ImageLoader.class) { if (mInstance == null) { mInstance = new ImageLoader(threadCount, type); } } } return mInstance; } /** * 根据path为imageview设置图片 * * @param path * @param imageView */ public void loadImage(final String path, final ImageView imageView, final boolean isFromNet) { imageView.setTag(path); if (mUIHandler == null) { mUIHandler = new Handler() { public void handleMessage(Message msg) { // 获取得到图片,为imageview回调设置图片 ImgBeanHolder holder = (ImgBeanHolder) msg.obj; Bitmap bm = holder.bitmap; ImageView imageview = holder.imageView; String path = holder.path; // 将path与getTag存储路径进行比较 if (imageview.getTag().toString().equals(path)) { imageview.setImageBitmap(bm); } }; }; } // 根据path在缓存中获取bitmap Bitmap bm = getBitmapFromLruCache(path); if (bm != null) { refreashBitmap(path, imageView, bm); } else { addTask(buildTask(path, imageView, isFromNet)); } } /** * 根据传入的参数,新建一个任务 * * @param path * @param imageView * @param isFromNet * @return */ private Runnable buildTask(final String path, final ImageView imageView, final boolean isFromNet) { return new Runnable() { @Override public void run() { Bitmap bm = null; if (isFromNet) { File file = getDiskCacheDir(imageView.getContext(), md5(path)); if (file.exists())// 如果在缓存文件中发现 { Log.e(TAG, "find image :" + path + " in disk cache ."); bm = loadImageFromLocal(file.getAbsolutePath(), imageView); } else { if (isDiskCacheEnable)// 检测是否开启硬盘缓存 { boolean downloadState = DownloadImgUtils.downloadImgByUrl(path, file); if (downloadState)// 如果下载成功 { Log.e(TAG, "download image :" + path + " to disk cache . path is " + file.getAbsolutePath()); bm = loadImageFromLocal(file.getAbsolutePath(), imageView); } } else // 直接从网络加载 { Log.e(TAG, "load image :" + path + " to memory."); bm = DownloadImgUtils.downloadImgByUrl(path, imageView); } } } else { bm = loadImageFromLocal(path, imageView); } // 3、把图片加入到缓存 addBitmapToLruCache(path, bm); refreashBitmap(path, imageView, bm); mSemaphoreThreadPool.release(); } }; } private Bitmap loadImageFromLocal(final String path, final ImageView imageView) { Bitmap bm; // 加载图片 // 图片的压缩 // 1、获得图片需要显示的大小 ImageSize imageSize = ImageSizeUtil.getImageViewSize(imageView); // 2、压缩图片 bm = decodeSampledBitmapFromPath(path, imageSize.width, imageSize.height); return bm; } /** * 从任务队列取出一个方法 * * @return */ private Runnable getTask() { if (mType == Type.FIFO) { return mTaskQueue.removeFirst(); } else if (mType == Type.LIFO) { return mTaskQueue.removeLast(); } return null; } /** * 利用签名辅助类,将字符串字节数组 * * @param str * @return */ public String md5(String str) { byte[] digest = null; try { MessageDigest md = MessageDigest.getInstance("md5"); digest = md.digest(str.getBytes()); return bytes2hex02(digest); } catch (NoSuchAlgorithmException e) { e.printStackTrace(); } return null; } /** * 方式二 * * @param bytes * @return */ public String bytes2hex02(byte[] bytes) { StringBuilder sb = new StringBuilder(); String tmp = null; for (byte b : bytes) { // 将每个字节与0xFF进行与运算,然后转化为10进制,然后借助于Integer再转化为16进制 tmp = Integer.toHexString(0xFF & b); if (tmp.length() == 1)// 每个字节8为,转为16进制标志,2个16进制位 { tmp = "0" + tmp; } sb.append(tmp); } return sb.toString(); } private void refreashBitmap(final String path, final ImageView imageView, Bitmap bm) { Message message = Message.obtain(); ImgBeanHolder holder = new ImgBeanHolder(); holder.bitmap = bm; holder.path = path; holder.imageView = imageView; message.obj = holder; mUIHandler.sendMessage(message); } /** * 将图片加入LruCache * * @param path * @param bm */ protected void addBitmapToLruCache(String path, Bitmap bm) { if (getBitmapFromLruCache(path) == null) { if (bm != null) mLruCache.put(path, bm); } } /** * 根据图片需要显示的宽和高对图片进行压缩 * * @param path * @param width * @param height * @return */ protected Bitmap decodeSampledBitmapFromPath(String path, int width, int height) { // 获得图片的宽和高,并不把图片加载到内存中 BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; BitmapFactory.decodeFile(path, options); options.inSampleSize = ImageSizeUtil.caculateInSampleSize(options, width, height); // 使用获得到的InSampleSize再次解析图片 options.inJustDecodeBounds = false; Bitmap bitmap = BitmapFactory.decodeFile(path, options); return bitmap; } private synchronized void addTask(Runnable runnable) { mTaskQueue.add(runnable); // if(mPoolThreadHandler==null)wait(); try { if (mPoolThreadHandler == null) mSemaphorePoolThreadHandler.acquire(); } catch (InterruptedException e) { } mPoolThreadHandler.sendEmptyMessage(0x110); } /** * 获得缓存图片的地址 * * @param context * @param uniqueName * @return */ public File getDiskCacheDir(Context context, String uniqueName) { String cachePath; if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) { cachePath = context.getExternalCacheDir().getPath(); } else { cachePath = context.getCacheDir().getPath(); } return new File(cachePath + File.separator + uniqueName); } /** * 根据path在缓存中获取bitmap * * @param key * @return */ private Bitmap getBitmapFromLruCache(String key) { return mLruCache.get(key); } private class ImgBeanHolder { Bitmap bitmap; ImageView imageView; String path; } }
相关工具类:
/** * @描述 获取图片大小工具类s * @项目名称 App_News * @包名 com.android.news.util * @类名 ImageSizeUtil * @author chenlin * @date 2014-3-7 下午7:37:50 * @version 1.0 */ public class ImageSizeUtil { /** * 根据需求的宽和高以及图片实际的宽和高计算SampleSize * * @param options * @param width * @param height * @return */ public static int caculateInSampleSize(Options options, int reqWidth, int reqHeight) { int width = options.outWidth; int height = options.outHeight; int inSampleSize = 1; if (width > reqWidth || height > reqHeight) { int widthRadio = Math.round(width * 1.0f / reqWidth); int heightRadio = Math.round(height * 1.0f / reqHeight); inSampleSize = Math.max(widthRadio, heightRadio); } return inSampleSize; } /** * 根据ImageView获适当的压缩的宽和高 * * @param imageView * @return */ public static ImageSize getImageViewSize(ImageView imageView) { ImageSize imageSize = new ImageSize(); DisplayMetrics displayMetrics = imageView.getContext().getResources().getDisplayMetrics(); LayoutParams lp = imageView.getLayoutParams(); int width = imageView.getWidth();// 获取imageview的实际宽度 if (lp != null) { if (width <= 0) { width = lp.width;// 获取imageview在layout中声明的宽度 } } if (width <= 0) { // width = imageView.getMaxWidth();// 检查最大值 width = getImageViewFieldValue(imageView, "mMaxWidth"); } if (width <= 0) { width = displayMetrics.widthPixels; } int height = imageView.getHeight();// 获取imageview的实际高度 if (lp != null) { if (height <= 0) { height = lp.height;// 获取imageview在layout中声明的宽度 } } if (height <= 0) { height = getImageViewFieldValue(imageView, "mMaxHeight");// 检查最大值 } if (height <= 0) { height = displayMetrics.heightPixels; } imageSize.width = width; imageSize.height = height; return imageSize; } public static class ImageSize { public int width; public int height; } /** * 通过反射获取imageview的某个属性值 * * @param object * @param fieldName * @return */ private static int getImageViewFieldValue(Object object, String fieldName) { int value = 0; try { Field field = ImageView.class.getDeclaredField(fieldName); field.setAccessible(true); int fieldValue = field.getInt(object); if (fieldValue > 0 && fieldValue < Integer.MAX_VALUE) { value = fieldValue; } } catch (Exception e) { } return value; } }
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