ImageCache 源码分析_技巧获得

ImageCache

 public static ImageCache getInstance(
            FragmentManager fragmentManager, ImageCacheParams cacheParams) {

        // Search for, or create an instance of the non-UI RetainFragment
        final RetainFragment mRetainFragment = findOrCreateRetainFragment(fragmentManager);

        // See if we already have an ImageCache stored in RetainFragment
        ImageCache imageCache = (ImageCache) mRetainFragment.getObject();

        // No existing ImageCache, create one and store it in RetainFragment
        if (imageCache == null) {
            imageCache = new ImageCache(cacheParams);
            mRetainFragment.setObject(imageCache);
        }

        return imageCache;
    }

 /**
     * A simple non-UI Fragment that stores a single Object and is retained over configuration
     * changes. It will be used to retain the ImageCache object.
     */
    public static class RetainFragment extends Fragment {
        private Object mObject;

        /**
         * Empty constructor as per the Fragment documentation
         */
        public RetainFragment() {}

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);

            // Make sure this Fragment is retained over a configuration change
            setRetainInstance(true);
        }

        /**
         * Store a single object in this Fragment.
         *
         * @param object The object to store
         */
        public void setObject(Object object) {
            mObject = object;
        }

        /**
         * Get the stored object.
         *
         * @return The stored object
         */
        public Object getObject() {
            return mObject;
        }
    }

发现在ImageCache单例中使用了一个 RetainFragment 并将单例ImageCache 放到其中，
这么做的原因：在使用和未使用Fragment的情况下，强制旋转屏幕，你会发现从保留内存缓存加载图片时几乎没有滞后。

参考资料

https://developer.android.com/samples/DisplayingBitmaps/src/com.example.android.displayingbitmaps/util/ImageCache.html#l105

http://www.trinea.cn/android/android-imagecache/