本文为分析
Fresco源码第一篇，基于fresco 1.8.1。
Fresco官网对于Fresco设计的基本概述
ImagePipeline
image pipeline 主要负责图片的加载和缓存工作。 可以从网路、本地内存、app res中加载图片。它具有三层缓存，其中两个在内存中，另一个在手机本地存储中。
Drawees
Drawees主要负责图片的展示工作。在图片完全加载之前他可以显示一个占位图，当图片不在屏幕上显示时，它可以自动释放图片所占用的内存。
从Fresco初始化看Fresco的基本组件
Fresco.java
public static void initialize(
Context context,
@Nullable ImagePipelineConfig imagePipelineConfig,
@Nullable DraweeConfig draweeConfig) {
//...
if (imagePipelineConfig == null) {
ImagePipelineFactory.initialize(context);
} else {
ImagePipelineFactory.initialize(imagePipelineConfig);
}
initializeDrawee(context, draweeConfig);
}
/** 初始化Drawee. */
private static void initializeDrawee(Context context,@Nullable DraweeConfig draweeConfig) {
sDraweeControllerBuilderSupplier =
new PipelineDraweeControllerBuilderSupplier(context, draweeConfig);
SimpleDraweeView.initialize(sDraweeControllerBuilderSupplier);
}
从Fresco的初始化可以看出Fresco的基本组件为：ImagePipeline和Drawee,接下来仔细看一下这两个都是负责哪些事情:
ImagePipeline
由于
ImagePipeLine是一个功能十分多的组件，它由ImagePipelineFactory负责创建，由ImagePipelineConfig负责配置。ImagePipelineFactory提供一些ImagePipeline组成的组件，比如缓存。
ImagePipelineConfig主要负责配置ImagePipeline的网络相关选项和缓存相关选项等等。
ImagePipelineFactory.java
public ImagePipeline getImagePipeline() {
if (mImagePipeline == null) {
mImagePipeline =
new ImagePipeline(
getProducerSequenceFactory(),
mConfig.getRequestListeners(),
mConfig.getIsPrefetchEnabledSupplier(),
getBitmapMemoryCache(),
getEncodedMemoryCache(),
getMainBufferedDiskCache(),
getSmallImageBufferedDiskCache(),
mConfig.getCacheKeyFactory(),
mThreadHandoffProducerQueue,
Suppliers.of(false));
}
return mImagePipeline;
}
ImagePipelineConfig.java
public class ImagePipelineConfig {
//...
private final NetworkFetcher mNetworkFetcher;
private final int mHttpNetworkTimeout;
@Nullable private final PlatformBitmapFactory mPlatformBitmapFactory;
private final PoolFactory mPoolFactory;
private final ProgressiveJpegConfig mProgressiveJpegConfig;
private final Set<RequestListener> mRequestListeners;
private final boolean mResizeAndRotateEnabledForNetwork;
private final DiskCacheConfig mSmallImageDiskCacheConfig;
@Nullable private final ImageDecoderConfig mImageDecoderConfig;
private final ImagePipelineExperiments mImagePipelineExperiments;
//...
}
Drawee
在上面的initializeDrawee()方法中可以看到，在初始化SimpleDraweeView之前，先初始化了PipelineDraweeControllerBuilderSupplier,那么这个类是干什么的？
PipelineDraweeControllerBuilderSupplier很简单，就是帮助PipelineDraweeControllerBuilder提供了ImagePipeline和PipelineDraweeControllerFactory。顾名思义, PipelineDraweeControllerFactory是用来生产PipelineDraweeController的。看源码可以知道，ImagePipeline是为方便PipelineDraweeController获得缓存。
PipelineDraweeControllerBuilder.java
@Override
protected PipelineDraweeController obtainController() {
DraweeController oldController = getOldController();
PipelineDraweeController controller;
if (oldController instanceof PipelineDraweeController) {
controller = (PipelineDraweeController) oldController;
controller.initialize(
obtainDataSourceSupplier(),
generateUniqueControllerId(),
getCacheKey(),
getCallerContext(),
mCustomDrawableFactories,
mImageOriginListener);
} else {
controller =
mPipelineDraweeControllerFactory.newController(
obtainDataSourceSupplier(),
generateUniqueControllerId(),
getCacheKey(),
getCallerContext(),
mCustomDrawableFactories,
mImageOriginListener);
}
return controller;
}
//CacheKey 由 mImagePipeline.getCacheKeyFactory()。提供
其实上面层层构造，最后是为了产生一个十分关键的对象PipelineDraweeController。
PipelineDraweeController
先来看一下官方注释：
Drawee controller that bridges the image pipeline with {@link SettableDraweeHierarchy}. <p> The
hierarchy's actual image is set to the image(s) obtained by the provided data source。
大致就是 PipelineDraweeController是ImagePipeline 和Drawee在图片处理流程中的结合点。即把ImagePipeline获取的图片数据传递给Drawee。
从这个类的属性也可以看出它所承担的工作:
PipelineDraweeController.java
//Drawee相关
private final Resources mResources;
private final DrawableFactory mAnimatedDrawableFactory;
@Nullable
private final ImmutableList<DrawableFactory> mGlobalDrawableFactories;
//数据缓存相关
private @Nullable MemoryCache<CacheKey, CloseableImage> mMemoryCache;
private CacheKey mCacheKey;
// Constant state (non-final because controllers can be reused)
private Supplier<DataSource<CloseableReference<CloseableImage>>> mDataSourceSupplier;
不过上面官方注释指出的是图片数据传递给了SettableDraweeHierarchy，而并没有直接传递给Drawee。那先看一眼SettableDraweeHierarchy这个类大概是干什么吧。
SettableDraweeHierarchy.java
Interface that represents a settable Drawee hierarchy. Hierarchy should display a placeholder
image until the actual image is set. In case of a failure, hierarchy can choose to display
a failure image.
恩，明白，大致是控制加载不同阶段图片显示的切换的
继续来看Drawee的初始化:
初始化所做的工作十分简单:
SimpleDraweeView.java
private void init(Context context, @Nullable AttributeSet attrs) {
if (isInEditMode()) {
return;
}
Preconditions.checkNotNull(
sDraweeControllerBuilderSupplier,
"SimpleDraweeView was not initialized!");
mSimpleDraweeControllerBuilder = sDraweeControllerBuilderSupplier.get();
if (attrs != null) {
TypedArray gdhAttrs = context.obtainStyledAttributes(
attrs,
R.styleable.SimpleDraweeView);
try {
if (gdhAttrs.hasValue(R.styleable.SimpleDraweeView_actualImageUri)) {
setImageURI(
Uri.parse(gdhAttrs.getString(R.styleable.SimpleDraweeView_actualImageUri)),
null);
} else if (gdhAttrs.hasValue((R.styleable.SimpleDraweeView_actualImageResource))) {
int resId = gdhAttrs.getResourceId(
R.styleable.SimpleDraweeView_actualImageResource,
NO_ID);
if (resId != NO_ID) {
setActualImageResource(resId);
}
}
} finally {
gdhAttrs.recycle();
}
}
}
判断SimpleDraweeControllerBuilder是否存在，不存在则初始化失败。如果设置SimpleDraweeView的属性，则对属性做相应的处理。
额。上面我们看了PipelineDraweeController。那SimpleDraweeController又是什么呢？
SimpleDraweeController
其实SimpleDraweeController就是PipelineDraweeController。这点可以从类的继承层次可以看出：
PipelineDraweeControllerBuilderSupplier implements Supplier<PipelineDraweeControllerBuilder>
PipelineDraweeControllerBuilder extends AbstractDraweeControllerBuilder<PipelineDraweeControllerBuilder
AbstractDraweeControllerBuilder <
BUILDER extends AbstractDraweeControllerBuilder<BUILDER, REQUEST, IMAGE, INFO>,
REQUEST,
IMAGE,
INFO>
implements SimpleDraweeControllerBuilder
上面对于Fresco的初始化大致已经分析完成了，对于Fresco图片加载的框架也基本比较清晰了，大概可以用下面这张图描述：
FrescoBasicArticture.png
可能存在一些问题，待后续完整阅读后，会慢慢更正。
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