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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