Fresco源码之DraweeController

DraweeController源码查看

首先看类的继承体系：
DraweeController
–| AbstractDraweeController
—-| PipelineDraweeController

DraweeController源码

DraweeController是一个接口，主要获取设置hierarchy，处理ontach,onTouch等事件
AbstractDraweeController：

构造主要设置线程池，重试手势相关的东西

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

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() {
    if (FLog.isLoggable(FLog.VERBOSE)) {
      FLog.v(
          TAG,
          "controller %x %s: onAttach: %s",
          System.identityHashCode(this),
          mId,
          mIsRequestSubmitted ? "request already submitted" : "request needs submit");
    }
    mEventTracker.recordEvent(Event.ON_ATTACH_CONTROLLER);
    Preconditions.checkNotNull(mSettableDraweeHierarchy);
    mDeferredReleaser.cancelDeferredRelease(this);
    mIsAttached = true;
    if (!mIsRequestSubmitted) {
      //发送请求
      submitRequest();
    }
  }

// 提交请求
protected void submitRequest() {
    mEventTracker.recordEvent(Event.ON_DATASOURCE_SUBMIT);
    getControllerListener().onSubmit(mId, mCallerContext);
    mSettableDraweeHierarchy.setProgress(0, true);
    mIsRequestSubmitted = true;
    mHasFetchFailed = false;
    // 获取数据源，这个数据源怎么获取的，我们目前不得而知
    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;
    final boolean wasImmediate = mDataSource.hasResult();

    // 请求结果的回调
    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);
  }

下面我们再看看请求成功了干了些什么：onNewResultInternal

private void onNewResultInternal(
      String id,
      DataSource<T> 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)

    // 判断是不是需要的数据，不是就释放资源
    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

     // 是想要的数据源，set image 同时释放之前缓存的图片
      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);
      }
    }
  }

PipelineDraweeController是AbstractDraweeController的子类也不需要过多打关注，我们现在有一个疑问点就是Fresco的数据请求是怎么发送出去的，又是怎么获取的，后面我们在一起读源代码。