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：

用于获取顶层的drawable

SettableDraweeHierachy：
图像可以被重置
图像可以设置进度
设置失败
设置重试
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

图像可以被重置
图像可以设置进度
设置失败
设置重试

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:

获取和设置Hieraychy
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:

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
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。

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
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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