Java tutorial
/* * Copyright 2012 Google Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.android.volley.cache; import android.annotation.TargetApi; import android.graphics.Bitmap; import android.os.Build; import android.os.Bundle; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.util.LruCache; import com.android.volley.VolleyLog; import com.android.volley.misc.Utils; import com.android.volley.toolbox.ImageCache; /** * This class holds our bitmap caches (memory and disk). */ public class BitmapCache implements ImageCache { private static final String TAG = "BitmapCache"; // Default memory cache size as a percent of device memory class private static final float DEFAULT_MEM_CACHE_PERCENT = 0.15f; private LruCache<String, Bitmap> mMemoryCache; /** * Don't instantiate this class directly, use * {@link #getInstance(android.support.v4.app.FragmentManager, float)}. * @param memCacheSize Memory cache size in KB. */ private BitmapCache(int memCacheSize) { init(memCacheSize); } /** * Find and return an existing BitmapCache stored in a {@link RetainFragment}, if not found a * new one is created using the supplied params and saved to a {@link RetainFragment}. * * @param fragmentManager The fragment manager to use when dealing with the retained fragment. * @param fragmentTag The tag of the retained fragment (should be unique for each memory cache * that needs to be retained). * @param memCacheSize Memory cache size in KB. */ public static BitmapCache getInstance(FragmentManager fragmentManager, String fragmentTag, int memCacheSize) { BitmapCache bitmapCache = null; RetainFragment mRetainFragment = null; if (fragmentManager != null) { // Search for, or create an instance of the non-UI RetainFragment mRetainFragment = getRetainFragment(fragmentManager, fragmentTag); // See if we already have a BitmapCache stored in RetainFragment bitmapCache = (BitmapCache) mRetainFragment.getObject(); } // No existing BitmapCache, create one and store it in RetainFragment if (bitmapCache == null) { bitmapCache = new BitmapCache(memCacheSize); if (mRetainFragment != null) { mRetainFragment.setObject(bitmapCache); } } return bitmapCache; } public static BitmapCache getInstance(FragmentManager fragmentManager, int memCacheSize) { return getInstance(fragmentManager, TAG, memCacheSize); } public static BitmapCache getInstance(FragmentManager fragmentManager, float memCachePercent) { return getInstance(fragmentManager, calculateMemCacheSize(memCachePercent)); } public static BitmapCache getInstance(FragmentManager fragmentManger) { return getInstance(fragmentManger, DEFAULT_MEM_CACHE_PERCENT); } /** * Initialize the cache. */ private void init(int memCacheSize) { // Set up memory cache VolleyLog.d(TAG, "Memory cache created (size = " + memCacheSize + "KB)"); mMemoryCache = new LruCache<String, Bitmap>(memCacheSize) { /** * Measure item size in kilobytes rather than units which is more practical * for a bitmap cache */ @Override protected int sizeOf(String key, Bitmap bitmap) { final int bitmapSize = getBitmapSize(bitmap) / 1024; return bitmapSize == 0 ? 1 : bitmapSize; } }; } /** * Adds a bitmap to both memory and disk cache. * @param data Unique identifier for the bitmap to store * @param bitmap The bitmap to store */ public void addBitmapToCache(String data, Bitmap bitmap) { if (data == null || bitmap == null) { return; } synchronized (mMemoryCache) { // Add to memory cache if (mMemoryCache.get(data) == null) { VolleyLog.d(TAG, "Memory cache put - " + data); mMemoryCache.put(data, bitmap); } } } /** * Get from memory cache. * * @param data Unique identifier for which item to get * @return The bitmap if found in cache, null otherwise */ public Bitmap getBitmapFromMemCache(String data) { if (data != null) { synchronized (mMemoryCache) { final Bitmap memBitmap = mMemoryCache.get(data); if (memBitmap != null) { VolleyLog.d(TAG, "Memory cache hit - " + data); return memBitmap; } } VolleyLog.d(TAG, "Memory cache miss - " + data); } return null; } /** * Clears the memory cache. */ public void clearCache() { if (mMemoryCache != null) { mMemoryCache.evictAll(); VolleyLog.d(TAG, "Memory cache cleared"); } } /** * Sets the memory cache size based on a percentage of the max available VM memory. * Eg. setting percent to 0.2 would set the memory cache to one fifth of the available * memory. Throws {@link IllegalArgumentException} if percent is < 0.05 or > .8. * memCacheSize is stored in kilobytes instead of bytes as this will eventually be passed * to construct a LruCache which takes an int in its constructor. * * This value should be chosen carefully based on a number of factors * Refer to the corresponding Android Training class for more discussion: * http://developer.android.com/training/displaying-bitmaps/ * * @param percent Percent of memory class to use to size memory cache * @return Memory cache size in KB */ public static int calculateMemCacheSize(float percent) { if (percent < 0.05f || percent > 0.8f) { throw new IllegalArgumentException( "setMemCacheSizePercent - percent must be " + "between 0.05 and 0.8 (inclusive)"); } return Math.round(percent * Runtime.getRuntime().maxMemory() / 1024); } /** * Get the size in bytes of a bitmap. */ @TargetApi(Build.VERSION_CODES.HONEYCOMB_MR1) public static int getBitmapSize(Bitmap bitmap) { if (Utils.hasHoneycombMR1()) { return bitmap.getByteCount(); } // Pre HC-MR1 return bitmap.getRowBytes() * bitmap.getHeight(); } /** * Locate an existing instance of this Fragment or if not found, create and * add it using FragmentManager. * * @param fm The FragmentManager manager to use. * @param fragmentTag The tag of the retained fragment (should be unique for each memory * cache that needs to be retained). * @return The existing instance of the Fragment or the new instance if just * created. */ private static RetainFragment getRetainFragment(FragmentManager fm, String fragmentTag) { // Check to see if we have retained the worker fragment. RetainFragment mRetainFragment = (RetainFragment) fm.findFragmentByTag(fragmentTag); // If not retained (or first time running), we need to create and add it. if (mRetainFragment == null) { mRetainFragment = new RetainFragment(); fm.beginTransaction().add(mRetainFragment, fragmentTag).commitAllowingStateLoss(); } return mRetainFragment; } @Override public Bitmap getBitmap(String key) { return getBitmapFromMemCache(key); } @Override public void putBitmap(String key, Bitmap bitmap) { addBitmapToCache(key, bitmap); } @Override public void invalidateBitmap(String url) { if (url == null) { return; } synchronized (mMemoryCache) { // Add to memory cache //if (mMemoryCache.get(data) == null) { VolleyLog.d(TAG, "Memory cache remove - " + url); mMemoryCache.remove(url); //} } } @Override public void clear() { clearCache(); } /** * A simple non-UI Fragment that stores a single Object and is retained over configuration * changes. It will be used to retain the BitmapCache 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; } } }