private LruCache<String, Bitmap> mMemoryCache;@Override
protected void onCreate(Bundle savedInstanceState) {...// Get max available VM memory, exceeding this amount will throw an// OutOfMemory exception. Stored in kilobytes as LruCache takes an// int in its constructor.final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);// Use 1/8th of the available memory for this memory cache.final int cacheSize = maxMemory / 8;mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {@Overrideprotected int sizeOf(String key, Bitmap bitmap) {// The cache size will be measured in kilobytes rather than// number of items.return bitmap.getByteCount() / 1024;}};...
}public void addBitmapToMemoryCache(String key, Bitmap bitmap) {if (getBitmapFromMemCache(key) == null) {mMemoryCache.put(key, bitmap);}
}public Bitmap getBitmapFromMemCache(String key) {return mMemoryCache.get(key);
}

public void loadBitmap(int resId, ImageView imageView) {final String imageKey = String.valueOf(resId);final Bitmap bitmap = getBitmapFromMemCache(imageKey);if (bitmap != null) {mImageView.setImageBitmap(bitmap);} else {mImageView.setImageResource(R.drawable.image_placeholder);BitmapWorkerTask task = new BitmapWorkerTask(mImageView);task.execute(resId);}
}

class BitmapWorkerTask extends AsyncTask<Integer, Void, Bitmap> {...// Decode image in background.@Overrideprotected Bitmap doInBackground(Integer... params) {final Bitmap bitmap = decodeSampledBitmapFromResource(getResources(), params[0], 100, 100));addBitmapToMemoryCache(String.valueOf(params[0]), bitmap);return bitmap;}...
}

private DiskLruCache mDiskLruCache;
private final Object mDiskCacheLock = new Object();
private boolean mDiskCacheStarting = true;
private static final int DISK_CACHE_SIZE = 1024 * 1024 * 10; // 10MB
private static final String DISK_CACHE_SUBDIR = "thumbnails";@Override
protected void onCreate(Bundle savedInstanceState) {...// Initialize memory cache...// Initialize disk cache on background threadFile cacheDir = getDiskCacheDir(this, DISK_CACHE_SUBDIR);new InitDiskCacheTask().execute(cacheDir);...
}class InitDiskCacheTask extends AsyncTask<File, Void, Void> {@Overrideprotected Void doInBackground(File... params) {synchronized (mDiskCacheLock) {File cacheDir = params[0];mDiskLruCache = DiskLruCache.open(cacheDir, DISK_CACHE_SIZE);mDiskCacheStarting = false; // Finished initializationmDiskCacheLock.notifyAll(); // Wake any waiting threads}return null;}
}class BitmapWorkerTask extends AsyncTask<Integer, Void, Bitmap> {...// Decode image in background.@Overrideprotected Bitmap doInBackground(Integer... params) {final String imageKey = String.valueOf(params[0]);// Check disk cache in background threadBitmap bitmap = getBitmapFromDiskCache(imageKey);if (bitmap == null) { // Not found in disk cache// Process as normalfinal Bitmap bitmap = decodeSampledBitmapFromResource(getResources(), params[0], 100, 100));}// Add final bitmap to cachesaddBitmapToCache(imageKey, bitmap);return bitmap;}...
}public void addBitmapToCache(String key, Bitmap bitmap) {// Add to memory cache as beforeif (getBitmapFromMemCache(key) == null) {mMemoryCache.put(key, bitmap);}// Also add to disk cachesynchronized (mDiskCacheLock) {if (mDiskLruCache != null && mDiskLruCache.get(key) == null) {mDiskLruCache.put(key, bitmap);}}
}public Bitmap getBitmapFromDiskCache(String key) {synchronized (mDiskCacheLock) {// Wait while disk cache is started from background threadwhile (mDiskCacheStarting) {try {mDiskCacheLock.wait();} catch (InterruptedException e) {}}if (mDiskLruCache != null) {return mDiskLruCache.get(key);}}return null;
}// Creates a unique subdirectory of the designated app cache directory. Tries to use external
// but if not mounted, falls back on internal storage.
public static File getDiskCacheDir(Context context, String uniqueName) {// Check if media is mounted or storage is built-in, if so, try and use external cache dir// otherwise use internal cache dirfinal String cachePath =Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) ||!isExternalStorageRemovable() ? getExternalCacheDir(context).getPath() :context.getCacheDir().getPath();return new File(cachePath + File.separator + uniqueName);
}

private LruCache<String, Bitmap> mMemoryCache;@Override
protected void onCreate(Bundle savedInstanceState) {...RetainFragment retainFragment =RetainFragment.findOrCreateRetainFragment(getFragmentManager());mMemoryCache = retainFragment.mRetainedCache;if (mMemoryCache == null) {mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {... // Initialize cache here as usual}retainFragment.mRetainedCache = mMemoryCache;}...
}class RetainFragment extends Fragment {private static final String TAG = "RetainFragment";public LruCache<String, Bitmap> mRetainedCache;public RetainFragment() {}public static RetainFragment findOrCreateRetainFragment(FragmentManager fm) {RetainFragment fragment = (RetainFragment) fm.findFragmentByTag(TAG);if (fragment == null) {fragment = new RetainFragment();fm.beginTransaction().add(fragment, TAG).commit();}return fragment;}@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setRetainInstance(true);}
}