ImageCache.java

/*
 * 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.example.android.contactslist.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;
import android.util.Log;

import com.example.android.contactslist.BuildConfig;

/**
 * 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
        if (BuildConfig.DEBUG) {
            Log.d(TAG, "Memory cache created (size = " + memCacheSize + ")");
        }
        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) {
                if (BuildConfig.DEBUG) {
                    Log.d(TAG, "Memory cache hit");
                }
                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;
        }
    }

}