Android四大圖片緩存框架之-Fresco之initialize（二） · Android開源框架學習系列

我們今天來了解下Fresco的初始化過程。以系統默認的初始化參數為例。 ~~~ Fresco.initialize(getApplicationContext()); ~~~ 進入到 com.facebook.drawee.backends.pipeline.Fresco中 ~~~ public static void initialize(Context context) { ImagePipelineFactory.initialize(context); initializeDrawee(context); } ~~~ 我們先看ImagePipelineFactory.initialize(context);方法 ~~~ public static void initialize(Context context) { initialize(ImagePipelineConfig.newBuilder(context).build()); } ~~~ 我們繼續看ImagePipelineConfig.newBuilder(context)方法， ~~~ public static ImagePipelineConfig.Builder newBuilder(Context context) { return new ImagePipelineConfig.Builder(context, null); } ~~~ 這里調用了ImagePipelineCongif的一個內部類Builder。 ~~~ private Builder(Context context) { this.mDownsampleEnabled = false; this.mResizeAndRotateEnabledForNetwork = true; this.mContext = (Context)Preconditions.checkNotNull(context); } ~~~ 這里只初始化了3個參數。其他的一些相關的參數并沒有在這里進行初始化，那么，其他的一些設置是怎么實現的呢。別著急，我們接下來看 ImagePipelineConfig.newBuilder(context).build()的build()方法。 ~~~ public ImagePipelineConfig build() { return new ImagePipelineConfig(this, null); } ~~~ 這里返回了ImagePipelineConfig的一個實例。我們看下他的構造函數吧。 ~~~ private ImagePipelineConfig(ImagePipelineConfig.Builder builder) { this.mAnimatedImageFactory = builder.mAnimatedImageFactory; this.mBitmapMemoryCacheParamsSupplier = (Supplier)(builder.mBitmapMemoryCacheParamsSupplier == null?new DefaultBitmapMemoryCacheParamsSupplier((ActivityManager)builder.mContext.getSystemService("activity")):builder.mBitmapMemoryCacheParamsSupplier); this.mCacheKeyFactory = (CacheKeyFactory)(builder.mCacheKeyFactory == null?DefaultCacheKeyFactory.getInstance():builder.mCacheKeyFactory); this.mContext = (Context)Preconditions.checkNotNull(builder.mContext); this.mDownsampleEnabled = builder.mDownsampleEnabled; this.mEncodedMemoryCacheParamsSupplier = (Supplier)(builder.mEncodedMemoryCacheParamsSupplier == null?new DefaultEncodedMemoryCacheParamsSupplier():builder.mEncodedMemoryCacheParamsSupplier); this.mImageCacheStatsTracker = (ImageCacheStatsTracker)(builder.mImageCacheStatsTracker == null?NoOpImageCacheStatsTracker.getInstance():builder.mImageCacheStatsTracker); this.mImageDecoder = builder.mImageDecoder; this.mIsPrefetchEnabledSupplier = builder.mIsPrefetchEnabledSupplier == null?new Supplier() { public Boolean get() { return Boolean.valueOf(true); } }:builder.mIsPrefetchEnabledSupplier; this.mMainDiskCacheConfig = builder.mMainDiskCacheConfig == null?getDefaultMainDiskCacheConfig(builder.mContext):builder.mMainDiskCacheConfig; this.mMemoryTrimmableRegistry = (MemoryTrimmableRegistry)(builder.mMemoryTrimmableRegistry == null?NoOpMemoryTrimmableRegistry.getInstance():builder.mMemoryTrimmableRegistry); this.mNetworkFetcher = (NetworkFetcher)(builder.mNetworkFetcher == null?new HttpUrlConnectionNetworkFetcher():builder.mNetworkFetcher); this.mPlatformBitmapFactory = builder.mPlatformBitmapFactory; this.mPoolFactory = builder.mPoolFactory == null?new PoolFactory(PoolConfig.newBuilder().build()):builder.mPoolFactory; this.mProgressiveJpegConfig = (ProgressiveJpegConfig)(builder.mProgressiveJpegConfig == null?new SimpleProgressiveJpegConfig():builder.mProgressiveJpegConfig); this.mRequestListeners = (Set)(builder.mRequestListeners == null?new HashSet():builder.mRequestListeners); this.mResizeAndRotateEnabledForNetwork = builder.mResizeAndRotateEnabledForNetwork; this.mSmallImageDiskCacheConfig = builder.mSmallImageDiskCacheConfig == null?this.mMainDiskCacheConfig:builder.mSmallImageDiskCacheConfig; int decodeThreads = this.mPoolFactory.getFlexByteArrayPoolMaxNumThreads(); this.mExecutorSupplier = (ExecutorSupplier)(builder.mExecutorSupplier == null?new DefaultExecutorSupplier():builder.mExecutorSupplier); } ~~~ 看到這里，就明白了，構造函數中根據判斷ImagePipelineConfig.Builder對象的成員變量是否為空來初始化，不為空，則用我們設置好的，為空，那么就用系統的。我們以mBitmapMemoryCacheParamsSupplier為例。 ~~~ public class DefaultBitmapMemoryCacheParamsSupplier implements Supplier<MemoryCacheParams> { private static final int MAX_CACHE_ENTRIES = 256; private static final int MAX_EVICTION_QUEUE_SIZE = 2147483647; private static final int MAX_EVICTION_QUEUE_ENTRIES = 2147483647; private static final int MAX_CACHE_ENTRY_SIZE = 2147483647; private final ActivityManager mActivityManager; public DefaultBitmapMemoryCacheParamsSupplier(ActivityManager activityManager) { this.mActivityManager = activityManager; } public MemoryCacheParams get() { return new MemoryCacheParams(this.getMaxCacheSize(), 256, 2147483647, 2147483647, 2147483647); } private int getMaxCacheSize() { int maxMemory = Math.min(this.mActivityManager.getMemoryClass() * 1048576, 2147483647); return maxMemory < 33554432?4194304:(maxMemory < 67108864?6291456:(VERSION.SDK_INT <= 9?8388608:maxMemory / 4)); } } ~~~ 看到這些敏感的數字就知道，這里就是配置LruCache大小的地方了。(猜測)。我想，這里會在某個地方調用get方法來獲取系統設置的參數。接著看下這些參數的意思。 ~~~ public MemoryCacheParams(int maxCacheSize, int maxCacheEntries, int maxEvictionQueueSize, int maxEvictionQueueEntries, int maxCacheEntrySize) { this.maxCacheSize = maxCacheSize; this.maxCacheEntries = maxCacheEntries; this.maxEvictionQueueSize = maxEvictionQueueSize; this.maxEvictionQueueEntries = maxEvictionQueueEntries; this.maxCacheEntrySize = maxCacheEntrySize; } ~~~ - 內存緩存的最大Size - 緩存的最大條目，應該就是緩存圖片的最大數目 - 驅逐隊列的Size，(以下是我猜測的內容，有待驗證)，驅逐隊列指的是重Lrucache中淘汰下來的圖片，但是近期可能會用到的，暫時存放在這里。 - 驅逐隊列的數目 - 單個緩存條目的最大大小以上純屬個人意見，如有錯誤，請及時更正。