Java tutorial
/* * Copyright (C) 2012 The Android Open Source Project * * 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.seun.gallery.util; import android.graphics.Bitmap; import android.graphics.Bitmap.Config; import android.graphics.BitmapFactory; import android.graphics.drawable.BitmapDrawable; 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 android.util.Log; import java.lang.ref.SoftReference; import java.util.Collections; import java.util.HashSet; import java.util.Iterator; import java.util.Set; public class ImageCache { private static final String TAG = "ImageCache"; public static boolean DEBUG = true; // Default memory cache size in kilobytes public static final int DEFAULT_MEM_CACHE_SIZE = 1024 * 5; // 5MB private LruCache<String, BitmapDrawable> mMemoryCache; private Set<SoftReference<Bitmap>> mReusableBitmaps; private ImageCache(int memoryCacheSize) { init(memoryCacheSize); } public static ImageCache getInstance(FragmentManager fragmentManager, int memoryCacheSize) { // 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(memoryCacheSize); mRetainFragment.setObject(imageCache); } return imageCache; } /** * Initialize the cache */ private void init(int memoryCacheSize) { //BEGIN_INCLUDE(init_memory_cache) // Set up memory cache if (DEBUG) { Log.d(TAG, "Memory cache created (size = " + memoryCacheSize + ")"); } // If we're running on Honeycomb or newer, create a set of reusable bitmaps that can be // populated into the inBitmap field of BitmapFactory.Options. Note that the set is // of SoftReferences which will actually not be very effective due to the garbage // collector being aggressive clearing Soft/WeakReferences. A better approach // would be to use a strongly references bitmaps, however this would require some // balancing of memory usage between this set and the bitmap LruCache. It would also // require knowledge of the expected size of the bitmaps. From Honeycomb to JellyBean // the size would need to be precise, from KitKat onward the size would just need to // be the upper bound (due to changes in how inBitmap can re-use bitmaps). if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { mReusableBitmaps = Collections.synchronizedSet(new HashSet<SoftReference<Bitmap>>()); } mMemoryCache = new LruCache<String, BitmapDrawable>(memoryCacheSize) { /** * Notify the removed entry that is no longer being cached */ @Override protected void entryRemoved(boolean evicted, String key, BitmapDrawable oldValue, BitmapDrawable newValue) { if (RecyclingBitmapDrawable.class.isInstance(oldValue)) { // The removed entry is a recycling drawable, so notify it // that it has been removed from the memory cache ((RecyclingBitmapDrawable) oldValue).setIsCached(false); } else { // The removed entry is a standard BitmapDrawable if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { // We're running on Honeycomb or later, so add the bitmap // to a SoftReference set for possible use with inBitmap later mReusableBitmaps.add(new SoftReference<Bitmap>(oldValue.getBitmap())); } } } /** * Measure item size in kilobytes rather than units which is more practical * for a bitmap cache */ @Override protected int sizeOf(String key, BitmapDrawable value) { final int bitmapSize = getBitmapSize(value) / 1024; return bitmapSize == 0 ? 1 : bitmapSize; } }; //END_INCLUDE(init_memory_cache) } /** * Adds a bitmap to both memory and disk cache. * * @param data Unique identifier for the bitmap to store * @param value The bitmap drawable to store */ public void addBitmapToCache(String data, BitmapDrawable value) { //BEGIN_INCLUDE(add_bitmap_to_cache) if (data == null || value == null) { return; } // Add to memory cache if (mMemoryCache != null) { if (RecyclingBitmapDrawable.class.isInstance(value)) { // The removed entry is a recycling drawable, so notify it // that it has been added into the memory cache ((RecyclingBitmapDrawable) value).setIsCached(true); } mMemoryCache.put(data, value); } //END_INCLUDE(add_bitmap_to_cache) } /** * Get from memory cache. * * @param data Unique identifier for which item to get * @return The bitmap drawable if found in cache, null otherwise */ public BitmapDrawable getBitmapFromMemCache(String data) { //BEGIN_INCLUDE(get_bitmap_from_mem_cache) BitmapDrawable memValue = null; if (mMemoryCache != null) { memValue = mMemoryCache.get(data); } if (DEBUG && memValue != null) { Log.d(TAG, "Memory cache hit"); } return memValue; //END_INCLUDE(get_bitmap_from_mem_cache) } /** * @param options - BitmapFactory.Options with out* options populated * @return Bitmap that case be used for inBitmap */ protected Bitmap getBitmapFromReusableSet(BitmapFactory.Options options) { //BEGIN_INCLUDE(get_bitmap_from_reusable_set) Bitmap bitmap = null; if (mReusableBitmaps != null && !mReusableBitmaps.isEmpty()) { final Iterator<SoftReference<Bitmap>> iterator = mReusableBitmaps.iterator(); Bitmap item; while (iterator.hasNext()) { item = iterator.next().get(); if (null != item && item.isMutable()) { // Check to see it the item can be used for inBitmap if (canUseForInBitmap(item, options)) { bitmap = item; // Remove from reusable set so it can't be used again iterator.remove(); break; } } else { // Remove from the set if the reference has been cleared. iterator.remove(); } } } return bitmap; //END_INCLUDE(get_bitmap_from_reusable_set) } /** * Clears both the memory and disk cache associated with this ImageCache object. Note that * this includes disk access so this should not be executed on the main/UI thread. */ public void clearCache() { if (mMemoryCache != null) { mMemoryCache.evictAll(); if (DEBUG) { Log.d(TAG, "Memory cache cleared"); } } } /** * @param candidate - Bitmap to check * @param targetOptions - Options that have the out* value populated * @return true if <code>candidate</code> can be used for inBitmap re-use with * <code>targetOptions</code> */ private static boolean canUseForInBitmap(Bitmap candidate, BitmapFactory.Options targetOptions) { //BEGIN_INCLUDE(can_use_for_inbitmap) if (!(Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT)) { // On earlier versions, the dimensions must match exactly and the inSampleSize must be 1 return candidate.getWidth() == targetOptions.outWidth && candidate.getHeight() == targetOptions.outHeight && targetOptions.inSampleSize == 1; } // From Android 4.4 (KitKat) onward we can re-use if the byte size of the new bitmap // is smaller than the reusable bitmap candidate allocation byte count. int width = targetOptions.outWidth / targetOptions.inSampleSize; int height = targetOptions.outHeight / targetOptions.inSampleSize; int byteCount = width * height * getBytesPerPixel(candidate.getConfig()); return byteCount <= (candidate.getRowBytes() * candidate.getHeight()); //END_INCLUDE(can_use_for_inbitmap) } /** * Return the byte usage per pixel of a bitmap based on its configuration. * * @param config The bitmap configuration. * @return The byte usage per pixel. */ private static int getBytesPerPixel(Config config) { if (config == Config.ARGB_8888) { return 4; } else if (config == Config.RGB_565) { return 2; } else if (config == Config.ARGB_4444) { return 2; } else if (config == Config.ALPHA_8) { return 1; } return 1; } /** * Get the size in bytes of a bitmap in a BitmapDrawable. Note that from Android 4.4 (KitKat) * onward this returns the allocated memory size of the bitmap which can be larger than the * actual bitmap data byte count (in the case it was re-used). * * @param value image * @return size in bytes */ public static int getBitmapSize(BitmapDrawable value) { Bitmap bitmap = value.getBitmap(); // 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. * @return The existing instance of the Fragment or the new instance if just * created. */ private static RetainFragment findOrCreateRetainFragment(FragmentManager fm) { //BEGIN_INCLUDE(find_create_retain_fragment) // Check to see if we have retained the worker fragment. RetainFragment mRetainFragment = (RetainFragment) fm.findFragmentByTag(TAG); // If not retained (or first time running), we need to create and add it. if (mRetainFragment == null) { mRetainFragment = new RetainFragment(); fm.beginTransaction().add(mRetainFragment, TAG).commitAllowingStateLoss(); } return mRetainFragment; //END_INCLUDE(find_create_retain_fragment) } /** * 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; } } }