Java tutorial
/* * Copyright (C) 2013 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.chris.ni.omw.util; import android.annotation.TargetApi; import android.graphics.Bitmap; import android.os.Bundle; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.util.LruCache; /** * This class holds our bitmap caches (memory and disk). */ public class ImageCache { private static final String TAG = "ImageCache"; private LruCache<String, Bitmap> mMemoryCache; /** * Creating a new ImageCache object using the specified parameters. * * @param memCacheSizePercent The cache size as a percent of available app memory. */ private ImageCache(float memCacheSizePercent) { init(memCacheSizePercent); } /** * Find and return an existing ImageCache 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 memCacheSizePercent The cache size as a percent of available app memory. * @return An existing retained ImageCache object or a new one if one did not exist */ public static ImageCache getInstance(FragmentManager fragmentManager, float memCacheSizePercent) { // 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(memCacheSizePercent); mRetainFragment.setObject(imageCache); } return imageCache; } /** * Initialize the cache. * * @param memCacheSizePercent The cache size as a percent of available app memory. */ private void init(float memCacheSizePercent) { int memCacheSize = calculateMemCacheSize(memCacheSizePercent); // Set up memory cache 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; } // Add to memory cache if (mMemoryCache != null && mMemoryCache.get(data) == null) { 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 (mMemoryCache != null) { final Bitmap memBitmap = mMemoryCache.get(data); if (memBitmap != null) { return memBitmap; } } return null; } /** * Get the size in bytes of a bitmap. * * @param bitmap The bitmap to calculate the size of. * @return size of bitmap in bytes. */ @TargetApi(12) public static int getBitmapSize(Bitmap bitmap) { if (Utils.hasHoneycombMR1()) { return bitmap.getByteCount(); } // Pre HC-MR1 return bitmap.getRowBytes() * bitmap.getHeight(); } /** * Calculates 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 available app memory to use to size memory cache. */ 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); } /** * 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. */ public static RetainFragment findOrCreateRetainFragment(FragmentManager fm) { // 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; } /** * 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; } } }