Fresco 源码分析(二) Fresco客户端与服务端交互(2) Fresco.initializeDrawee()分析 续

4.2.1.2 Fresco.initializeDrawee()的过程 续

继续上篇博客的分析Fresco.initializeDrawee()

    sDraweeControllerBuilderSupplier = new PipelineDraweeControllerBuilderSupplier(context);
    SimpleDraweeView.initialize(sDraweeControllerBuilderSupplier);

1. 初始化了一个sDraweeControllerBuilderSupplier
2. 将此sDraweeControllerBuilderSupplier用于初始化SimpleDraweeView

还是老的分析思路： 一步一步分析

4.2.1.2.1 sDraweeControllerBuilderSupplier初始化的过程

public PipelineDraweeControllerBuilderSupplier(Context context) {
    this(context, ImagePipelineFactory.getInstance());
  }

  public PipelineDraweeControllerBuilderSupplier(
      Context context,
      ImagePipelineFactory imagePipelineFactory) {
    this(context, imagePipelineFactory, null);
  }

  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;
  } 

构造方法，相互调用，总结过程

1. 获取到了ImagePipelineFactory的实例，经过查看源码，只是将Fresco第一步初始化中的ImagePipelineFactory,获取到了这个实例,这里采用了单例的形式

2. 获取到ImagePipleline，并且保存在这个Supplier中,这个里面代码看似只有这么几行，但是包涵的内容很多，还是先从广度看，然后再从深度看（这个方面作为遗留的Q2，一会儿再看）
   *** ImagePipelineFactory.getImagePipeline（）源码 ***

   public ImagePipeline getImagePipeline() {
   if (mImagePipeline == null) {
   mImagePipeline =
   new ImagePipeline(
   getProducerSequenceFactory(),
   mConfig.getRequestListeners(),
   mConfig.getIsPrefetchEnabledSupplier(),
   getBitmapMemoryCache(),
   getEncodedMemoryCache(),
   mConfig.getCacheKeyFactory());
   }
   return mImagePipeline;
   }

在获取ImagePipeline（）中，如果为空，创建了一个
3. 创建了一个PipelineDraweeControllerFactory，并且保存到这个Supplier中

看到这里，我们先继续的广度分析，就是继续的分析SimpleDraweeView.initialize(sDraweeControllerBuilderSupplier)的过程

4.2.1.2.2 SimpleDraweeView.initialize(sDraweeControllerBuilderSupplier)的过程

在上面的分析，我们已经看到sDraweeControllerBuilderSupplier使用的是PipelineDraweeControllerBuilderSupplier
接下来，我们就看SimpleDraweeView.initialize(sDraweeControllerBuilderSupplier)的过程
从下面的代码，我们看到sDraweeControllerBuilderSupplier保存在了SimpleDraweeView中，SimpleDraweeView能够很简单的使用，是因为Fresco帮助我们在这里初始化了很多东西

  private static Supplier<? extends SimpleDraweeControllerBuilder> sDraweeControllerBuilderSupplier;

  /** Initializes {@link SimpleDraweeView} with supplier of Drawee controller builders. */
  public static void initialize(
      Supplier<? extends SimpleDraweeControllerBuilder> draweeControllerBuilderSupplier) {
    sDraweeControllerBuilderSupplier = draweeControllerBuilderSupplier;
  }

接着，以SimpleDraweeView的xml解析的方式来分析初始化的过程，我们发现，这里调用了我们的sDraweeControllerBuilderSupplier的get方法
*** SimpleDraweeView 的xml构造方式源码分析 ***

  public SimpleDraweeView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  private void init() {
    if (isInEditMode()) {
      return;
    }
    Preconditions.checkNotNull(
        sDraweeControllerBuilderSupplier,
        "SimpleDraweeView was not initialized!");
    mSimpleDraweeControllerBuilder = sDraweeControllerBuilderSupplier.get();
  }

先别着急，我们再接着看，在使用xml解析的方式，我们还用到了一个setImageUri方法，再接着看这个方法，在setImageUri中，创建了一个DraweeController，然后设置给了自身，在构造DraweeController的时候，我们发现，调用了mSimpleDraweeControllerBuilder的build()方法

*** setImageURI（Uri）的源码分析 ***

  /**
   * Displays an image given by the uri.
   *
   * @param uri uri of the image
   * @undeprecate
   */
  @Override
  public void setImageURI(Uri uri) {
    setImageURI(uri, null);
  }

  /**
   * Displays an image given by the uri.
   *
   * @param uri uri of the image
   * @param callerContext caller context
   */
  public void setImageURI(Uri uri, @Nullable Object callerContext) {
    DraweeController controller = mSimpleDraweeControllerBuilder
        .setCallerContext(callerContext)
        .setUri(uri)
        .setOldController(getController())
        .build();
    setController(controller);
  }

到这里，我们先总结一下：

1. SimpleDraweeView中的sDraweeControllerBuilderSupplier是PipelineDraweeControllerBuilderSupplier
2. SimpleDraweeView中的controller是什么呢？那么这里就需要看看sDraweeControllerBuilderSupplier的get到什么ControllerBuilder？
3. 对应的ControllerBuilder，build出什么controller
4. controller又是怎么样将提交请求的
5. 遗留的Q2问题什么时候可以分析

看到这几个问题，我们发现，我们的分析，任重而道远

4.2.1.2.3 PipelineDraweeControllerBuilderSupplier的get()分析

这里只是创建了一个PipelineDraweeControllerBuilder，并且这个builder保存了imagePipeline和mPipelineDraweeControllerFactory

*** PipelineDraweeControllerBuilder.get()分析 ***
@Override
public PipelineDraweeControllerBuilder get() {
return new PipelineDraweeControllerBuilder(
mContext,
mPipelineDraweeControllerFactory,
mImagePipeline,
mBoundControllerListeners);
}

*** PipelineDraweeControllerBuilder的构造方法 ***
在这里，我们看不到什么，那么就继续看build()方法吧
public PipelineDraweeControllerBuilder(
Context context,
PipelineDraweeControllerFactory pipelineDraweeControllerFactory,
ImagePipeline imagePipeline,
Set boundControllerListeners) {
super(context, boundControllerListeners);
mImagePipeline = imagePipeline;
mPipelineDraweeControllerFactory = pipelineDraweeControllerFactory;
}

查看build方法时，便已经看到了这个PipelineDraweeControllerBuilder的继承结构

AbstractDraweeControllerBuilder
--| VolleyDraweeControllerBuilder
--|　PipelineDraweeControllerBuilder

Volley相关的我们就不看了，这个是和Vollery框架结合使用的，有兴趣可以自己研究下，大同小异

这次直接从方法调用来看即可，这次我们就要看到请求到底是如何产生的了

*** AbstractDraweeControllerBuilder.build()方法源码分析 ***
非核心代码，这次就忽略了，我们主要目的是要看到如何发送请求的，到后面请求如何反馈到前台，我们再详细分析其他代码
在build中，最关键的是buildController（），而在buildController中，最核心的是obtainController()，然后其他的是设置请求的一些信息，比如说设置请求的ImageRequest，其他的是设置重试等等

  /** Builds the specified controller. */
  @Override
  public AbstractDraweeController build() {
    validate();

    // if only a low-res request is specified, treat it as a final request.
    if (mImageRequest == null && mMultiImageRequests == null && mLowResImageRequest != null) {
      mImageRequest = mLowResImageRequest;
      mLowResImageRequest = null;
    }

    return buildController();
  }


  /** Builds a regular controller. */
  protected AbstractDraweeController buildController() {
    AbstractDraweeController controller = obtainController();
    maybeBuildAndSetRetryManager(controller);
    maybeAttachListeners(controller);
    return controller;
  }

  /** Concrete builder classes should override this method to return a new controller. */
  protected abstract AbstractDraweeController obtainController();

而在这里，发现obtainController（）是抽象方法，那么就是找子类呗
*** PipelineDraweeControllerBuilder.obtainController()源码分析 ***
在获取controller的方法中，我们还是以第一次初始化为例，那么就是else的部分，这里就是用mPipelineDraweeControllerFactory创建了一个newController
@Override
protected PipelineDraweeController obtainController() {
DraweeController oldController = getOldController();
PipelineDraweeController controller;
if (oldController instanceof PipelineDraweeController) {
controller = (PipelineDraweeController) oldController;
controller.initialize(
obtainDataSourceSupplier(),
generateUniqueControllerId(),
getCallerContext());
} else {
controller = mPipelineDraweeControllerFactory.newController(
obtainDataSourceSupplier(),
generateUniqueControllerId(),
getCallerContext());
}
return controller;
}

这块要关键的分析了，因为已经到了重点了

  controller = mPipelineDraweeControllerFactory.newController(
      obtainDataSourceSupplier(),
      generateUniqueControllerId(),
      getCallerContext());

我们一步一步看

1. obtainDataSourceSupplier()获取到了一个DataSourceSupplier
2. 然后mPipelineDraweeControllerFactory类new了一个controller

这也没看出来什么，是吧，我们下节就得来点插叙，结合DraweeController和这里的获取Supplier直接的关系，那么基本的请求流程，我们算基本分析结束

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