Fresco 源码分析(一) DraweeView-DraweeHierarchy-DraweeController(MVC) DraweeHierachy+DraweeController的分析

4.1.5.2 模型层DraweeHierachy继承体系以及各个类的作用

DraweeHierachy (I)
--| SettableDraweeHierarchy (I)
------| GenericDraweeHierarchy

DraweeHierachy：

1. 用于获取顶层的drawable
   SettableDraweeHierachy：
2. 图像可以被重置
3. 图像可以设置进度
4. 设置失败
5. 设置重试
6. 设置controllerOverlay

在理解获取顶层的Drawable时，需要首先理解Drawable的继承结构

先来看看DraweeHierachy的源码，发现其为接口，并且只有一个方法，就是用于获取顶层的Drawable

DraweeHierachy的源码

public interface DraweeHierarchy {

  /**
   * Returns the top level drawable in the corresponding hierarchy. Hierarchy should always have
   * the same instance of its top level drawable.
   * @return top level drawable
   */
  public Drawable getTopLevelDrawable();
}

再来看看继承其的接口，SettableDraweeHierachy，如上所述

1. 图像可以被重置

2. 图像可以设置进度

3. 设置失败

4. 设置重试

5. 设置controllerOverlay

    public interface SettableDraweeHierarchy extends DraweeHierarchy {
      public void reset();
      public void setImage(Drawable drawable, float progress, boolean immediate);
      public void setProgress(float progress, boolean immediate);
      public void setFailure(Throwable throwable);
      public void setRetry(Throwable throwable);
      public void setControllerOverlay(Drawable drawable);
    }
   

4.1.5.3 控制层DraweeController继承体系以及个各类的作用

DraweeController
--| AbstractDraweeController
----| PipelineDraweeController

DraweeController:

1. 获取和设置Hieraychy
2. view的各种事件通知过来，controller来控制这些逻辑的操作（onAttach/onDetach/onTouchEvent/getAnimatable）

AbstractDraweeController:

1. 最关键的功能： 实现了客户端向服务端的提交请求，即向DataSource中注册观察者，在有结果返回的时候，在主线程通知客户端更新即可，即设置Hierarychy的drawable即可

2. 参照之前的分析方式，仍然采用先构造，然后具体方法的顺序
   2.1 构造方法，设置了UI线程池，重试，以及手势相关的信息

   public AbstractDraweeController(
   DeferredReleaser deferredReleaser,
   Executor uiThreadImmediateExecutor,
   String id,
   Object callerContext) {
   mDeferredReleaser = deferredReleaser;
   mUiThreadImmediateExecutor = uiThreadImmediateExecutor;
   init(id, callerContext);
   }

   /**
   * Initializes this controller with the new id and caller context.
   * This allows for reusing of the existing controller instead of instantiating a new one.
   * This method should be called when the controller is in detached state.
   * @param id unique id for this controller
   * @param callerContext tag and context for this controller
   */
   protected void initialize(String id, Object callerContext) {
   init(id, callerContext);
   }

   private void init(String id, Object callerContext) {
   mEventTracker.recordEvent(Event.ON_INIT_CONTROLLER);
   // cancel deferred release
   if (mDeferredReleaser != null) {
   mDeferredReleaser.cancelDeferredRelease(this);
   }
   // reinitialize mutable state (fetch state)
   mIsAttached = false;
   releaseFetch();
   // reinitialize optional components
   if (mRetryManager != null) {
   mRetryManager.init();
   }
   if (mGestureDetector != null) {
   mGestureDetector.init();
   mGestureDetector.setClickListener(this);
   }
   if (mControllerListener instanceof InternalForwardingListener) {
   ((InternalForwardingListener) mControllerListener).clearListeners();
   } else {
   mControllerListener = null;
   }
   // clear hierarchy and controller overlay
   if (mSettableDraweeHierarchy != null) {
   mSettableDraweeHierarchy.reset();
   mSettableDraweeHierarchy.setControllerOverlay(null);
   mSettableDraweeHierarchy = null;
   }
   mControllerOverlay = null;
   // reinitialize constant state
   if (FLog.isLoggable(FLog.VERBOSE)) {
   FLog.v(TAG, "controller %x %s -> %s: initialize", System.identityHashCode(this), mId, id);
   }
   mId = id;
   mCallerContext = callerContext;
   }

   2.2 具体方法，在这里做分析时，我们重点关注图片如何获取，因而我们关注的核心方法是onAttach()，在这里实现了图片请求的机制，以及图片获取到如何回调，如何显示到UI层的控制，在下面的程序中，看到核心的设置的方法是submitRequest()

   @Override
   public void onAttach() {
   // 记录log
   if (FLog.isLoggable(FLog.VERBOSE)) {
   FLog.v(
   TAG,
   "controller %x %s: onAttach: %s",
   System.identityHashCode(this),mId,
   mIsRequestSubmitted ? "request already submitted" : "request needs submit");
   }
   //-------------事件跟踪
   mEventTracker.recordEvent(Event.ON_ATTACH_CONTROLLER);
   Preconditions.checkNotNull(mSettableDraweeHierarchy);
   mDeferredReleaser.cancelDeferredRelease(this);
   mIsAttached = true;
   // --------如果是为请求的状态，发送请求！！！！！！！！！！！！！！
   if (!mIsRequestSubmitted) {
   submitRequest();
   }
   }

此处以第一次请求为例，这样分析比较简单，查看下面的方法，在请求时，设置请求的进度为0，获取到数据源(DataSource)，然后给数据源注册观察者(DataSubscriber)，先查看下面的SubmitRequest方法

protected void submitRequest() {
    mEventTracker.recordEvent(Event.ON_DATASOURCE_SUBMIT);
    getControllerListener().onSubmit(mId, mCallerContext);
    mSettableDraweeHierarchy.setProgress(0, true);
    mIsRequestSubmitted = true;
    mHasFetchFailed = false;
    mDataSource = getDataSource();
    if (FLog.isLoggable(FLog.VERBOSE)) {
      FLog.v(
          TAG,
          "controller %x %s: submitRequest: dataSource: %x",
          System.identityHashCode(this),
          mId,
          System.identityHashCode(mDataSource));
    }
    final String id = mId;
	//------------此处以第一次请求为例，所以wasImmediate为false
    final boolean wasImmediate = mDataSource.hasResult();
	//------------创建dataSubscriber的匿名内部类，交由AbstractDraweeController处理
	//------------回调的结果
    final DataSubscriber<T> dataSubscriber =
        new BaseDataSubscriber<T>() {
          @Override
          public void onNewResultImpl(DataSource<T> dataSource) {
            // isFinished must be obtained before image, otherwise we might set intermediate result
            // as final image.
            boolean isFinished = dataSource.isFinished();
            float progress = dataSource.getProgress();
            T image = dataSource.getResult();
            if (image != null) {
              onNewResultInternal(id, dataSource, image, progress, isFinished, wasImmediate);
            } else if (isFinished) {
              onFailureInternal(id, dataSource, new NullPointerException(), /* isFinished */ true);
            }
          }
          @Override
          public void onFailureImpl(DataSource<T> dataSource) {
            onFailureInternal(id, dataSource, dataSource.getFailureCause(), /* isFinished */ true);
          }
          @Override
          public void onProgressUpdate(DataSource<T> dataSource) {
            boolean isFinished = dataSource.isFinished();
            float progress = dataSource.getProgress();
            onProgressUpdateInternal(id, dataSource, progress, isFinished);
          }
        };
	//-----------给数据源注册观察者
    mDataSource.subscribe(dataSubscriber, mUiThreadImmediateExecutor);
  }

到了这里，一次请求已经完成了，请求的结果会在回调中执行，但是请求是如何生成的呢？我们并没有看到具体发送请求的逻辑，这个疑问我们先记录下来（暂且标记为Q1）。先来看看对于请求结果是如何处理的，以新的一次请求结果为例，onNewResultImpl（）方法，而onNewResultImpl方法，以image不为空为例，最终会调用AbstractDraweeController.onNewResultInternal()方法。下面我们来看看，是如何处理这次新的请求的结果。

1. 判断是否是想要的数据源，即查看数据信息是否是当前请求的信息，如果不是，直接释放了资源

2. 如果是想要的数据源，创建对应的drawable，设置当前显示的drawable，释放之前缓存的drawable对象和Image对象

   private void onNewResultInternal(
   String id,
   DataSource dataSource,
   @Nullable T image,
   float progress,
   boolean isFinished,
   boolean wasImmediate) {
   // ignore late callbacks (data source that returned the new result is not the one we expected)
   if (!isExpectedDataSource(id, dataSource)) {
   logMessageAndImage("ignore_old_datasource @ onNewResult", image);
   releaseImage(image);
   dataSource.close();
   return;
   }
   mEventTracker.recordEvent(
   isFinished ? Event.ON_DATASOURCE_RESULT : Event.ON_DATASOURCE_RESULT_INT);
   // create drawable
   Drawable drawable;
   try {
   drawable = createDrawable(image);
   } catch (Exception exception) {
   logMessageAndImage("drawable_failed @ onNewResult", image);
   releaseImage(image);
   onFailureInternal(id, dataSource, exception, isFinished);
   return;
   }
   T previousImage = mFetchedImage;
   Drawable previousDrawable = mDrawable;
   mFetchedImage = image;
   mDrawable = drawable;
   try {
   // set the new image
   if (isFinished) {
   logMessageAndImage("set_final_result @ onNewResult", image);
   mDataSource = null;
   mSettableDraweeHierarchy.setImage(drawable, 1f, wasImmediate);
   getControllerListener().onFinalImageSet(id, getImageInfo(image), getAnimatable());
   // IMPORTANT: do not execute any instance-specific code after this point
   } else {
   logMessageAndImage("set_intermediate_result @ onNewResult", image);
   mSettableDraweeHierarchy.setImage(drawable, progress, wasImmediate);
   getControllerListener().onIntermediateImageSet(id, getImageInfo(image));
   // IMPORTANT: do not execute any instance-specific code after this point
   }
   } finally {
   if (previousDrawable != null && previousDrawable != drawable) {
   releaseDrawable(previousDrawable);
   }
   if (previousImage != null && previousImage != image) {
   logMessageAndImage("release_previous_result @ onNewResult", previousImage);
   releaseImage(previousImage);
   }
   }
   }

好了，就是获取到图像后续的操作，这个其实就是我们UI的操作，分析到此即可，其他的情况，我们参照这个分析的方式分析即可。下面我们来解决一下之前的Q1问题,数据源的请求是如何发送出去的，这个问题就比较复杂了，我们需要通过至少四篇的博客来分析这个请求的过程。
下篇博客：Fresco 源码分析(二) Fresco客户端与服务端交互(1) 解决遗留的Q1问题 ：http://www.cnblogs.com/pandapan/p/4646786.html

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