Fresco源码解析 - 创建一个ImagePipeline（一）

在Fresco源码解析 - 初始化过程分析章节中，

我们分析了Fresco的初始化过程，两个initialize方法中都用到了 ImagePipelineFactory类。

 

ImagePipelineFactory.initialize(context);

会创建一个所有参数都使用默认值的ImagePipelineConfig来初始化ImagePipeline。

 

ImagePipelineFactory.initialize(imagePipelineConfig)会首先用 imagePipelineConfig创建一个ImagePipelineFactory的实例 - sInstance。

 

sInstance = new ImagePipelineFactory(imagePipelineConfig);

然后，初始化Drawee时，在PipelineDraweeControllerBuilderSupplier的构造方法中通过 ImagePipelineFactory.getInstance()获取这个实例。

 

Fresco.java

 

private static void initializeDrawee(Context context) {

 sDraweeControllerBuilderSupplier = new PipelineDraweeControllerBuilderSupplier(context);

 SimpleDraweeView.initialize(sDraweeControllerBuilderSupplier);

PipelineDraweeControllerBuilderSupplier.java

public PipelineDraweeControllerBuilderSupplier(Context context) {

 this(context, ImagePipelineFactory.getInstance());

public PipelineDraweeControllerBuilderSupplier(

 Context context,

 ImagePipelineFactory imagePipelineFactory) {

 this(context, imagePipelineFactory, null);

} 

PipelineDraweeControllerBuilderSupplier还有一个构造方法，就是 this(context, imagePipelineFactory, null)调用的构造方法。

 

public PipelineDraweeControllerBuilderSupplier(

 Context context,

 ImagePipelineFactory imagePipelineFactory,

 Set ControllerListener boundControllerListeners) {

 mContext = context;

 mImagePipeline = imagePipelineFactory.getImagePipeline();

 mPipelineDraweeControllerFactory = new PipelineDraweeControllerFactory(

 context.getResources(),

 DeferredReleaser.getInstance(),

 imagePipelineFactory.getAnimatedDrawableFactory(),

 UiThreadImmediateExecutorService.getInstance());

 mBoundControllerListeners = boundControllerListeners;

} 

其中，mImagePipeline = imagePipelineFactory.getImagePipeline()用于获取ImagePipeline的实例。

 

ImagePipelineFactory.java

 

public ImagePipeline getImagePipeline() {

 if (mImagePipeline == null) {

 mImagePipeline =

 new ImagePipeline(

 getProducerSequenceFactory(),

 mConfig.getRequestListeners(),

 mConfig.getIsPrefetchEnabledSupplier(),

 getBitmapMemoryCache(),

 getEncodedMemoryCache(),

 mConfig.getCacheKeyFactory());

 return mImagePipeline;

}

可以看出mImagePipeline是一个单例，构造ImagePipeline时用到的mConfig就是本片最开始讲到的 ImagePipelineConfig imagePipelineConfig。

 

经过这个过程，一个ImagePipeline就被创建好了，下面我们具体解析一下ImagePipeline的每个参数。

 

因为ImagePipelineFactory用ImagePipelineConfig来创建一个ImagePipeline，我们首先分析一下ImagePipelineConfig的源码。

 

public class ImagePipelineConfig {

 private final Supplier MemoryCacheParams mBitmapMemoryCacheParamsSupplier;

 private final CacheKeyFactory mCacheKeyFactory;

 private final Context mContext;

 private final Supplier MemoryCacheParams mEncodedMemoryCacheParamsSupplier;

 private final ExecutorSupplier mExecutorSupplier;

 private final ImageCacheStatsTracker mImageCacheStatsTracker;

 private final AnimatedDrawableUtil mAnimatedDrawableUtil;

 private final AnimatedImageFactory mAnimatedImageFactory;

 private final ImageDecoder mImageDecoder;

 private final Supplier Boolean mIsPrefetchEnabledSupplier;

 private final DiskCacheConfig mMainDiskCacheConfig;

 private final MemoryTrimmableRegistry mMemoryTrimmableRegistry;

 private final NetworkFetcher mNetworkFetcher;

 private final PoolFactory mPoolFactory;

 private final ProgressiveJpegConfig mProgressiveJpegConfig;

 private final Set RequestListener mRequestListeners;

 private final boolean mResizeAndRotateEnabledForNetwork;

 private final DiskCacheConfig mSmallImageDiskCacheConfig;

 private final PlatformBitmapFactory mPlatformBitmapFactory;

 // other methods

}

 

 

上图可以看出，获取图像的第一站是Memeory Cache，然后是Disk Cache，最后是Network，而Memory和Disk都是缓存在本地的数据，MemoryCacheParams就用于表示它们的缓存策略。

 

MemoryCacheParams.java

 

 /**

 * Pass arguments to control the caches behavior in the constructor.

 * @param maxCacheSize The maximum size of the cache, in bytes.

 * @param maxCacheEntries The maximum number of items that can live in the cache.

 * @param maxEvictionQueueSize The eviction queue is an area of memory that stores items ready

 * for eviction but have not yet been deleted. This is the maximum

 * size of that queue in bytes.

 * @param maxEvictionQueueEntries The maximum number of entries in the eviction queue.

 * @param maxCacheEntrySize The maximum size of a single cache entry.

 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;

 }

 

关于每个参数的作用，注释已经写得很清楚，不再赘述。

 

CacheKeyFactory会为ImageRequest创建一个索引 - CacheKey。

 

/**

 * Factory methods for creating cache keys for the pipeline.

public interface CacheKeyFactory {

 * @return {@link CacheKey} for doing bitmap cache lookups in the pipeline.

 public CacheKey getBitmapCacheKey(ImageRequest request);

 * @return {@link CacheKey} for doing encoded image lookups in the pipeline.

 public CacheKey getEncodedCacheKey(ImageRequest request);

 * @return a {@link String} that unambiguously indicates the source of the image.

 public Uri getCacheKeySourceUri(Uri sourceUri);

}

ExecutorSupplier会根据ImagePipeline的使用场景获取不同的Executor。

 

public interface ExecutorSupplier {

 /** Executor used to do all disk reads, whether for disk cache or local files. */

 Executor forLocalStorageRead();

 /** Executor used to do all disk writes, whether for disk cache or local files. */

 Executor forLocalStorageWrite();

 /** Executor used for all decodes. */

 Executor forDecode();

 /** Executor used for all image transformations, such as transcoding, resizing, and rotating. */

 Executor forTransform();

 /** Executor used for background operations, such as postprocessing. */

 Executor forBackground();

}

ImageCacheStatsTracker 作为 Cache 埋点工具，可以统计Cache的各种操作数据。

 

public interface ImageCacheStatsTracker {

 /** Called whenever decoded images are put into the bitmap cache. */

 public void onBitmapCachePut();

 /** Called on a bitmap cache hit. */

 public void onBitmapCacheHit();

 /** Called on a bitmap cache miss. */

 public void onBitmapCacheMiss();

 /** Called whenever encoded images are put into the encoded memory cache. */

 public void onMemoryCachePut();

 /** Called on an encoded memory cache hit. */

 public void onMemoryCacheHit();

 /** Called on an encoded memory cache hit. */

 public void onMemoryCacheMiss();

 * Called on an staging area hit.

 * p The staging area stores encoded images. It gets the images before they are written

 * to disk cache.

 public void onStagingAreaHit();

 /** Called on a staging area miss hit. */

 public void onStagingAreaMiss();

 /** Called on a disk cache hit. */

 public void onDiskCacheHit();

 /** Called on a disk cache miss. */

 public void onDiskCacheMiss();

 /** Called if an exception is thrown on a disk cache read. */

 public void onDiskCacheGetFail();

 * Registers a bitmap cache with this tracker.

 * p Use this method if you need access to the cache itself to compile your stats.

 public void registerBitmapMemoryCache(CountingMemoryCache ?, ? bitmapMemoryCache);

 * Registers an encoded memory cache with this tracker.

 * p Use this method if you need access to the cache itself to compile your stats.

 public void registerEncodedMemoryCache(CountingMemoryCache ?, ? encodedMemoryCache);

}

剩下的几个参数与Drawable关联比较大，我们下一篇再分析。 
在进行插件化时，需要先将插件加载到当前进程中来，插件通常以APK的形式保存在SD卡上，VirtualApk加载插件的过程如下：PluginManager.loadPlugin---- LoadedPlugin.create，最终会创建LoadedPlugin对象，该对象就表示插件在内存中的存在形式。
奥特曼超人 KARL-Dujinyang-奥特曼超人。作者目前任职于银狐、泡椒游戏公司，曾任职腾为CTO，CSDN技术专家，曾创办过创业go、造梦工厂、米奇云，万能孵化器等，领域涉及逆向安全专家以及全栈工程师，作者目前出书中。