android 加载大量图片不卡顿

来源：互联网发布：mac免费版ps软件下载编辑：程序博客网时间：2024/05/29 02:21
本博客为 http://www.imooc.com/view/489 的笔记
/** * 通过路径获取图片,然后对图片进行压缩 存入缓存中 更新界面 *  * 通过将任务存入任务队列中,通知轮询线程从任务队列中获取任务的方法, * 来解决大量图片加载过程中 滑动卡顿的问题(核心解决办法) *  */public class ImageLoader{    /**     * 图片缓存的核心类     */    private LruCache<String, Bitmap> mLruCache;    /**     * 线程池     */    private ExecutorService mThreadPool;    /**     * 线程池的线程数量，默认为1     */    private int mThreadCount = 3;    /**     * 队列的调度方式     */    private Type mType = Type.LIFO;    /**     * 任务队列     */    private LinkedList<Runnable> mTasks;    /**     * 轮询的线程     */    private Thread mPoolThread;    private Handler mPoolThreadHander;    /**     * 运行在UI线程的handler，用于给ImageView设置图片     */    private Handler mHandler;    /**     * 引入一个值为1的信号量，防止mPoolThreadHander未初始化完成     */    private volatile Semaphore mSemaphore = new Semaphore(0);    /**     * 引入一个值为1的信号量，由于线程池内部也有一个阻塞线程，防止加入任务的速度过快，使LIFO效果不明显     */    private volatile Semaphore mPoolSemaphore;    private static ImageLoader mInstance;    /**     * 队列的调度方式     *      * @author zhy     *      */    public enum Type    {        FIFO, LIFO    }    /**     * 单例获得该实例对象     *      * @return     */    public static ImageLoader getInstance()    {        if (mInstance == null)        {            synchronized (ImageLoader.class)            {                if (mInstance == null)                {                    mInstance = new ImageLoader(1, Type.LIFO);                }            }        }        return mInstance;    }    private ImageLoader(int threadCount, Type type)    {        init(threadCount, type);    }    private void init(int threadCount, Type type)    {        // loop thread        mPoolThread = new Thread()        {            @Override            public void run()            {                Looper.prepare();                mPoolThreadHander = new Handler()                {                    @Override                    public void handleMessage(Message msg)                    {                        mThreadPool.execute(getTask());                        try                        {                            mPoolSemaphore.acquire();                        } catch (InterruptedException e)                        {                        }                    }                };                // 释放一个信号量                mSemaphore.release();                Looper.loop();            }        };        mPoolThread.start();        // 获取应用程序最大可用内存        int maxMemory = (int) Runtime.getRuntime().maxMemory();        int cacheSize = maxMemory / 4;        mLruCache = new LruCache<String, Bitmap>(cacheSize)        {            @Override            protected int sizeOf(String key, Bitmap value)            {                return value.getRowBytes() * value.getHeight();            };        };        mThreadPool = Executors.newFixedThreadPool(threadCount);        mPoolSemaphore = new Semaphore(threadCount);        mTasks = new LinkedList<Runnable>();        mType = type == null ? Type.LIFO : type;    }    /**     * 加载图片     *      * @param path     * @param imageView     */    public void loadImage(final String path, final ImageView imageView)    {        // set tag        imageView.setTag(path);        // UI线程        if (mHandler == null)        {            mHandler = new Handler()            {                @Override                public void handleMessage(Message msg)                {                    ImgBeanHolder holder = (ImgBeanHolder) msg.obj;                    ImageView imageView = holder.imageView;                    Bitmap bm = holder.bitmap;                    String path = holder.path;                    if (imageView.getTag().toString().equals(path))                    {                        imageView.setImageBitmap(bm);                    }                }            };        }        Bitmap bm = getBitmapFromLruCache(path);        if (bm != null)        {            ImgBeanHolder holder = new ImgBeanHolder();            holder.bitmap = bm;            holder.imageView = imageView;            holder.path = path;            Message message = Message.obtain();            message.obj = holder;            mHandler.sendMessage(message);        } else        {            addTask(new Runnable()            {                @Override                public void run()                {                    ImageSize imageSize = getImageViewWidth(imageView);                    int reqWidth = imageSize.width;                    int reqHeight = imageSize.height;                    Bitmap bm = decodeSampledBitmapFromResource(path, reqWidth,                            reqHeight);                    addBitmapToLruCache(path, bm);                    ImgBeanHolder holder = new ImgBeanHolder();                    holder.bitmap = getBitmapFromLruCache(path);                    holder.imageView = imageView;                    holder.path = path;                    Message message = Message.obtain();                    message.obj = holder;                    // Log.e("TAG", "mHandler.sendMessage(message);");                    mHandler.sendMessage(message);                    mPoolSemaphore.release();                }            });        }    }    /**     * 添加一个任务     *      * @param runnable     */    private synchronized void addTask(Runnable runnable)    {        try        {            // 请求信号量，防止mPoolThreadHander为null            if (mPoolThreadHander == null)                mSemaphore.acquire();        } catch (InterruptedException e)        {        }        mTasks.add(runnable);        mPoolThreadHander.sendEmptyMessage(0x110);    }    /**     * 取出一个任务     *      * @return     */    private synchronized Runnable getTask()    {        if (mType == Type.FIFO)        {            return mTasks.removeFirst();        } else if (mType == Type.LIFO)        {            return mTasks.removeLast();        }        return null;    }    /**     * 单例获得该实例对象     *      * @return     */    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ImageView获得适当的压缩的宽和高     *      * @param imageView     * @return     */    private ImageSize getImageViewWidth(ImageView imageView)    {        ImageSize imageSize = new ImageSize();        final DisplayMetrics displayMetrics = imageView.getContext()                .getResources().getDisplayMetrics();        final LayoutParams params = imageView.getLayoutParams();        int width = params.width == LayoutParams.WRAP_CONTENT ? 0 : imageView                .getWidth(); // Get actual image width        if (width <= 0)            width = params.width; // Get layout width parameter        if (width <= 0)            width = getImageViewFieldValue(imageView, "mMaxWidth"); // Check                                                                    // maxWidth                                                                    // parameter        if (width <= 0)            width = displayMetrics.widthPixels;        int height = params.height == LayoutParams.WRAP_CONTENT ? 0 : imageView                .getHeight(); // Get actual image height        if (height <= 0)            height = params.height; // Get layout height parameter        if (height <= 0)            height = getImageViewFieldValue(imageView, "mMaxHeight"); // Check                                                                        // maxHeight                                                                        // parameter        if (height <= 0)            height = displayMetrics.heightPixels;        imageSize.width = width;        imageSize.height = height;        return imageSize;    }    /**     * 从LruCache中获取一张图片，如果不存在就返回null。     */    private Bitmap getBitmapFromLruCache(String key)    {        return mLruCache.get(key);    }    /**     * 往LruCache中添加一张图片     *      * @param key     * @param bitmap     */    private void addBitmapToLruCache(String key, Bitmap bitmap)    {        if (getBitmapFromLruCache(key) == null)        {            if (bitmap != null)                mLruCache.put(key, bitmap);        }    }    /**     * 计算inSampleSize，用于压缩图片     *      * @param options     * @param reqWidth     * @param reqHeight     * @return     */    private int calculateInSampleSize(BitmapFactory.Options options,            int reqWidth, int reqHeight)    {        // 源图片的宽度        int width = options.outWidth;        int height = options.outHeight;        int inSampleSize = 1;        if (width > reqWidth && height > reqHeight)        {            // 计算出实际宽度和目标宽度的比率            int widthRatio = Math.round((float) width / (float) reqWidth);            int heightRatio = Math.round((float) width / (float) reqWidth);            inSampleSize = Math.max(widthRatio, heightRatio);        }        return inSampleSize;    }    /**     * 根据计算的inSampleSize，得到压缩后图片     *      * @param pathName     * @param reqWidth     * @param reqHeight     * @return     */    private Bitmap decodeSampledBitmapFromResource(String pathName,            int reqWidth, int reqHeight)    {        // 第一次解析将inJustDecodeBounds设置为true，来获取图片大小        final BitmapFactory.Options options = new BitmapFactory.Options();        options.inJustDecodeBounds = true;        BitmapFactory.decodeFile(pathName, options);        // 调用上面定义的方法计算inSampleSize值        options.inSampleSize = calculateInSampleSize(options, reqWidth,                reqHeight);        // 使用获取到的inSampleSize值再次解析图片        options.inJustDecodeBounds = false;        Bitmap bitmap = BitmapFactory.decodeFile(pathName, options);        return bitmap;    }    private class ImgBeanHolder    {        Bitmap bitmap;        ImageView imageView;        String path;    }    private class ImageSize    {        int width;        int height;    }    /**     * 反射获得ImageView设置的最大宽度和高度     *      * @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 = (Integer) field.get(object);            if (fieldValue > 0 && fieldValue < Integer.MAX_VALUE)            {                value = fieldValue;                Log.e("TAG", value + "");            }        } catch (Exception e)        {        }        return value;    }}
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