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,
DataSourcedataSource,
@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
安卓源码分析群: Android源码分析QQ1群号:164812238
