android 缓存Bitmap 使用内存缓存

private LruCache<String, Bitmap> mMemoryCache;

    /**
     * 判断内存大小 设置位图的缓存空间
     */
    private void judgeMemory() {
        final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
        final int cacheSize = maxMemory / 8;

        mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
            @Override
            protected int sizeOf(String key, Bitmap bitmap) {
                return bitmap.getByteCount() / 1024;
            }
        };
    }

    /**
     * 将位图添加到缓存中
     *
     * @param key    key值
     * @param bitmap 放入的位图
     */
    private void addBitmapToMemoryCache(String key, Bitmap bitmap) {
        if (getBitmapFromMemCache(key) == null) {
            mMemoryCache.put(key, bitmap);
        }
    }

    /**
     * 从缓存中得到位图
     *
     * @param key key值
     * @return 返回取出的位图
     */
    private Bitmap getBitmapFromMemCache(String key) {
        return mMemoryCache.get(key);
    }

    /**
     * 检索AsyncTask是否已经被分配到指定的ImageView:
     *
     * @param imageView 传入imageview控件
     * @return 返回已经被分配指定的imageview
     */
    private static BitmapWorkTask getBitmapWorkerTask(ImageView imageView) {
        if (imageView != null) {
            final Drawable drawable = imageView.getDrawable();
            if (drawable instanceof AsyncDrawable) {
                final AsyncDrawable asyncDrawable = (AsyncDrawable) drawable;
                return asyncDrawable.getBitmapWorkTask();
            }
        }
        return null;
    }

    /**
     * 创建一个专用的Drawable的子类来储存任务的引用。
     */
    class AsyncDrawable extends BitmapDrawable {
        private final WeakReference bitmapWorkerTaskReference;

        public AsyncDrawable(Resources res, Bitmap bitmap, BitmapWorkTask bitmapWorkTask) {
            super(res, bitmap);
            bitmapWorkerTaskReference = new WeakReference(bitmapWorkTask);
        }

        public BitmapWorkTask getBitmapWorkTask() {
            return (BitmapWorkTask) bitmapWorkerTaskReference.get();
        }
    }

在doInBackground中添加到缓存

        protected Bitmap doInBackground(Integer... integers) {
            final Bitmap bitmap = decodeSampleBitmapFromResources(getResources(), integers[0], 100, 100);
            addBitmapToMemoryCache(String.valueOf(integers[0]), bitmap);
            return bitmap;
        }

然后在oncreate中 加载，首先判断从缓存中加载。

if (bitmap != null) {
                imageView.setImageBitmap(bitmap);
            } else {
                final BitmapWorkTask task = new BitmapWorkTask(imageView);
                final AsyncDrawable asyncDrawable = new AsyncDrawable(getResources(), decodeSampleBitmapFromResources(getResources(), resId, imageView.getMaxWidth(), imageView.getMaxHeight()), task);
                imageView.setImageDrawable(asyncDrawable);
                task.execute(resId);
            }