Android-Fresco系列2 加载资源
16lz
2021-01-23
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流程图如下：
一、SimpleDraweeView加载图片
val draweeView = findViewById<SimpleDraweeView>(R.id.my_image_view)draweeView.setImageURI("http://ww1.sinaimg.cn/large/610dc034ly1fjaxhky81vj20u00u0ta1.jpg")通过setImageURI函数设置图片加载，参数是Uri参数或图片地址。
1) setImageURI
//SimpleDraweeViewpublic void setImageURI(Uri uri, @Nullable Object callerContext) { DraweeController controller = mControllerBuilder .setCallerContext(callerContext) .setUri(uri) .setOldController(getController()) .build(); setController(controller);}从这个方法开始了图片加载之旅。比较重要的是两个类PipelineDraweeControllerBuilder，AbstractDraweeControllerBuilder，前者继承自后者。
2) PipelineDraweeControllerBuilder
- callerContext参数默认为null。
- mControllerBuilder对象在SimpleDraweeView的init方法中初始化。
- setUri在PipelineDraweeControllerBuilder类中
//PipelineDraweeControllerBuilder@Overridepublic PipelineDraweeControllerBuilder setUri(@Nullable Uri uri) { if (uri == null) { return super.setImageRequest(null); } ImageRequest imageRequest = ImageRequestBuilder.newBuilderWithSource(uri) .setRotationOptions(RotationOptions.autoRotateAtRenderTime()) .build(); return super.setImageRequest(imageRequest);}3) ImageRequest
ImageRequestBuilder类构建了一个ImageRequest对象，build方法是：
//ImageRequestBuilderpublic ImageRequest build() { validate(); return new ImageRequest(this);}validate用于检查图片地址。
ImageRequest构造函数主要初始化了以下参数：
mCacheChoice//缓存选择mSourceUri//地址mSourceUriType//地址类型，网络，本地，asset，resourcemProgressiveRenderingEnabled//进度渲染是否允许mLocalThumbnailPreviewsEnabled//本地略缩图预览是否允许mImageDecodeOptions//图片解码选项mResizeOptions//裁剪mRotationOptions//旋转mIsDiskCacheEnabled//磁盘缓存mIsMemoryCacheEnabled//内存缓存...4) AbstractDraweeControllerBuilder
最后还要调用一下父类AbstractDraweeControllerBuilder的setImageRequest方法，初始化以下mImageRequest对象：
//AbstractDraweeControllerBuilderpublic BUILDER setImageRequest(REQUEST imageRequest) { mImageRequest = imageRequest; return getThis();}- setOldController
getController方法先获取一下前一个Controller，然后设置到AbstractDraweeControllerBuilder类中。
- build
定义在AbstractDraweeControllerBuilder类中：
//AbstractDraweeControllerBuilder@Overridepublic AbstractDraweeController build() { return buildController();}//AbstractDraweeControllerBuilderprotected AbstractDraweeController buildController() { AbstractDraweeController controller = obtainController(); return controller;}5) PipelineDraweeControllerBuilder
- obtainController
obtainController方法定义在PipelineDraweeControllerBuilder类中：
//PipelineDraweeControllerBuilder@Overrideprotected PipelineDraweeController obtainController() { try { DraweeController oldController = getOldController(); PipelineDraweeController controller; final String controllerId = generateUniqueControllerId(); if (oldController instanceof PipelineDraweeController) { controller = (PipelineDraweeController) oldController; } else { controller = mPipelineDraweeControllerFactory.newController(); } controller.initialize( obtainDataSourceSupplier(controller, controllerId), controllerId, getCacheKey(), getCallerContext(), mCustomDrawableFactories, mImageOriginListener); return controller; } finally { }}设置Controller的时候，先判断前一个controller是否存在，存在的话获取旧的，并强转成PipelineDraweeController类型，否则新建一个。
6) PipelineDraweeControllerFactory
- newController
一般情况下，第一次加载都是新建：
//PipelineDraweeControllerFactorypublic PipelineDraweeController newController() { PipelineDraweeController controller = internalCreateController( mResources, mDeferredReleaser, mAnimatedDrawableFactory, mUiThreadExecutor, mMemoryCache, mDrawableFactories); return controller;}protected PipelineDraweeController internalCreateController() { return new PipelineDraweeController( resources, deferredReleaser, animatedDrawableFactory, uiThreadExecutor, memoryCache, drawableFactories);}最终返回一个PipelineDraweeController对象。然后执行对象的initialize方法，在执行这个方法之前，里面有一个参数是通过obtainDataSourceSupplier方法获取的,另外一个是getCacheKey，先看看这两个方法再(这个方法涉及的流程比较长，删除部分不关心的代码)：
- obtainDataSourceSupplier
//AbstractDraweeControllerBuilderprotected Supplier<DataSource<IMAGE>> obtainDataSourceSupplier( final DraweeController controller, final String controllerId) { Supplier<DataSource<IMAGE>> supplier = null; // final image supplier; if (mImageRequest != null) { supplier = getDataSourceSupplierForRequest(controller, controllerId, mImageRequest); } else if (mMultiImageRequests != null) { supplier = getFirstAvailableDataSourceSupplier( controller, controllerId, mMultiImageRequests, mTryCacheOnlyFirst); } return supplier;}即使走getFirstAvailableDataSourceSupplier分支，也会调用getDataSourceSupplierForRequest方法，看看这个方法：
- getDataSourceSupplierForRequest
//AbstractDraweeControllerBuilder/** Creates a data source supplier for the given image request. */protected Supplier<DataSource<IMAGE>> getDataSourceSupplierForRequest( final DraweeController controller, final String controllerId, final REQUEST imageRequest, final CacheLevel cacheLevel) { final Object callerContext = getCallerContext(); return new Supplier<DataSource<IMAGE>>() { @Override public DataSource<IMAGE> get() { return getDataSourceForRequest( controller, controllerId, imageRequest, callerContext, cacheLevel); } @Override public String toString() { return Objects.toStringHelper(this).add("request", imageRequest.toString()).toString(); } };}到这里可以缓一缓，因为返回了一个Supplier对象，而且新建这个对象的时候在实现get方法的时候返回了一个getDataSourceForRequest方法，这个方法在PipelineDraweeControllerBuilder类中定义，先不看。
- getCacheKey
获取缓存key。
//PipelineDraweeControllerBuilderprivate @Nullable CacheKey getCacheKey() { final ImageRequest imageRequest = getImageRequest(); final CacheKeyFactory cacheKeyFactory = mImagePipeline.getCacheKeyFactory(); CacheKey cacheKey = null; if (cacheKeyFactory != null && imageRequest != null) { if (imageRequest.getPostprocessor() != null) { cacheKey = cacheKeyFactory.getPostprocessedBitmapCacheKey( imageRequest, getCallerContext()); } else { cacheKey = cacheKeyFactory.getBitmapCacheKey( imageRequest, getCallerContext()); } } return cacheKey;}cacheKeyFactory的初始化是在ImagePipelineConfig的构造函数中：
//ImagePipelineConfigmCacheKeyFactory = builder.mCacheKeyFactory == null ? DefaultCacheKeyFactory.getInstance() : builder.mCacheKeyFactory;看看DefaultCacheKeyFactory类中怎么返回缓存key的：
//DefaultCacheKeyFactory@Overridepublic CacheKey getBitmapCacheKey(ImageRequest request, Object callerContext) { return new BitmapMemoryCacheKey( getCacheKeySourceUri(request.getSourceUri()).toString(), request.getResizeOptions(), request.getRotationOptions(), request.getImageDecodeOptions(), null, null, callerContext);}其实是返回一个BitmapMemoryCacheKey对象，这个对象继承自CacheKey。
回到obtainController方法中调用的initialize方法，再看看：
//PipelineDraweeControllerpublic void initialize( Supplier<DataSource<CloseableReference<CloseableImage>>> dataSourceSupplier, String id, CacheKey cacheKey, Object callerContext, @Nullable ImmutableList<DrawableFactory> customDrawableFactories, @Nullable ImageOriginListener imageOriginListener) { super.initialize(id, callerContext); mDataSourceSupplier = dataSourceSupplier; mCacheKey = cacheKey;}主要初始化了几个对象。
获取controller对象完毕之后，就开始执行setController方法：
- setController
//DraweeView/** Sets the controller. */public void setController(@Nullable DraweeController draweeController) { mDraweeHolder.setController(draweeController); super.setImageDrawable(mDraweeHolder.getTopLevelDrawable());}DraweeHolder中定义了setController方法：
//DraweeHolderpublic void setController(@Nullable DraweeController draweeController) { boolean wasAttached = mIsControllerAttached; if (wasAttached) { detachController(); } // Clear the old controller if (isControllerValid()) { mController.setHierarchy(null); } mController = draweeController; if (mController != null) { mController.setHierarchy(mHierarchy); } else { } if (wasAttached) { attachController(); }}二、视图可见性发生变化
可以看到此时wasAttached为false，这样一来detachController和attachController方法都无法调用了，调用栈流程到这里仿佛中断了。
1) GenericDraweeView
记得在GenericDraweeView在构造函数中会执行inflateHierarchy方法：
//GenericDraweeViewprotected void inflateHierarchy(Context context, @Nullable AttributeSet attrs) { GenericDraweeHierarchyBuilder builder = GenericDraweeHierarchyInflater.inflateBuilder(context, attrs); setAspectRatio(builder.getDesiredAspectRatio()); setHierarchy(builder.build());}2) DraweeHolder
重新看看setHierarchy，最终调用到DraweeHolder的setHierarchy方法：
//DraweeHolderpublic void setHierarchy(DH hierarchy) { mEventTracker.recordEvent(Event.ON_SET_HIERARCHY); final boolean isControllerValid = isControllerValid(); setVisibilityCallback(null); mHierarchy = Preconditions.checkNotNull(hierarchy); Drawable drawable = mHierarchy.getTopLevelDrawable(); onVisibilityChange(drawable == null || drawable.isVisible()); setVisibilityCallback(this); if (isControllerValid) { mController.setHierarchy(hierarchy); }}这里有一个setVisibilityCallback方法，设置了visiable监听：
//DraweeHolderprivate void setVisibilityCallback(@Nullable VisibilityCallback visibilityCallback) { Drawable drawable = getTopLevelDrawable(); if (drawable instanceof VisibilityAwareDrawable) { ((VisibilityAwareDrawable) drawable).setVisibilityCallback(visibilityCallback); }}getTopLevelDrawable方法获取的是mHierarchy对象的Drawable，而mHierarchy方法对应GenericDraweeHierarchy类，这个类里面的getTopLevelDrawable方法对应的是RootDrawable，它继承自ForwardingDrawable类，它又继承自Android原生Drawable。所以实际上是设置了Drawable可见性监听。当收到可见性变化时，先在ForwardingDrawable接收到回调信号：
//ForwardingDrawable@Overridepublic boolean setVisible(boolean visible, boolean restart) { final boolean superResult = super.setVisible(visible, restart); if (mCurrentDelegate == null) { return superResult; } return mCurrentDelegate.setVisible(visible, restart); }mCurrentDelegate是RootDrawable：
//RootDrawable@Overridepublic boolean setVisible(boolean visible, boolean restart) { if (mVisibilityCallback != null) { mVisibilityCallback.onVisibilityChange(visible); } return super.setVisible(visible, restart);}终于看到回调方法的地方了，刚才说到DraweeHolder设置了监听，那么在DraweeHolder中看看回调逻辑：
//DraweeHolder@Overridepublic void onVisibilityChange(boolean isVisible) { mIsVisible = isVisible; attachOrDetachController();}//DraweeHolderprivate void attachOrDetachController() { if (mIsHolderAttached && mIsVisible) { attachController(); } else { detachController(); }}如果holder没有附属到view上时，将其连接上，否则剥离掉。
先看看attachController函数：
- attachController
if (mController != null && mController.getHierarchy() != null) { mController.onAttach();}开始在Controller类中执行onAttach方法，这个方法实现在AbstractDraweeController类中，定义在DraweeController接口中。
//AbstractDraweeController@Override public void onAttach() { if (!mIsRequestSubmitted) { submitRequest(); }}核心方法就两行代码，提交刚才的请求：
//AbstractDraweeControllerprotected void submitRequest() { final T closeableImage = getCachedImage(); if (closeableImage != null) { onImageLoadedFromCacheImmediately(mId, closeableImage); onNewResultInternal(mId, mDataSource, closeableImage, 1.0f, true, true, true); return; } mSettableDraweeHierarchy.setProgress(0, true); mIsRequestSubmitted = true; mHasFetchFailed = false; mDataSource = getDataSource(); final String id = mId; final boolean wasImmediate = mDataSource.hasResult(); 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(); boolean hasMultipleResults = dataSource.hasMultipleResults(); float progress = dataSource.getProgress(); T image = dataSource.getResult(); if (image != null) { onNewResultInternal( id, dataSource, image, progress, isFinished, wasImmediate, hasMultipleResults); } 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); } }; mDataSource.subscribe(dataSubscriber, mUiThreadImmediateExecutor);}这个方法里面是核心的代码，分为两个部分，前一个部分是找本地缓存，有缓存的话，直接取缓存数据展示然后返回，否则就去请求并加载。
3) 取内存缓存
先看取缓存,getCachedImage:
//PipelineDraweeController @Override protected @Nullable CloseableReference<CloseableImage> getCachedImage() { try { if (mMemoryCache == null || mCacheKey == null) { return null; } // We get the CacheKey CloseableReference<CloseableImage> closeableImage = mMemoryCache.get(mCacheKey); if (closeableImage != null && !closeableImage.get().getQualityInfo().isOfFullQuality()) { closeableImage.close(); return null; } return closeableImage; } finally { }}从内存缓存中取数据，是CloseableImage类型的，取到缓存并符合质量条件就返回，对于不符合质量条件的关闭closeableImage并返回null，关闭的过程实际是在一个SharedReference对象中将CloseableImage对象的引用计数删除或计数减一。
后续单独讲缓存策略。
获取到缓存之后，执行onImageLoadedFromCacheImmediately通知消息注册者，从内存取到缓存数据了。
4) 显示内存缓存图片
onNewResultInternal才是真正加载图片的地方：
//AbstractDraweeControllerprivate void onNewResultInternal( String id, DataSource<T> dataSource, @Nullable T image, float progress, boolean isFinished, boolean wasImmediate, boolean deliverTempResult) { try { Drawable drawable; try { drawable = createDrawable(image); } catch (Exception exception) { } try { // set the new image if (isFinished) { mDataSource = null; mSettableDraweeHierarchy.setImage(drawable, 1f, wasImmediate); } } finally { releaseDrawable(previousDrawable); } } finally { }}先看看createDrawable的代码：
//PipelineDraweeController@Overrideprotected Drawable createDrawable(CloseableReference<CloseableImage> image) { drawable = mDefaultDrawableFactory.createDrawable(closeableImage); if (drawable != null) { return drawable; }}//DefaultDrawableFactory@Override@Nullablepublic Drawable createDrawable(CloseableImage closeableImage) { try { if (closeableImage instanceof CloseableStaticBitmap) { CloseableStaticBitmap closeableStaticBitmap = (CloseableStaticBitmap) closeableImage; Drawable bitmapDrawable = new BitmapDrawable(mResources, closeableStaticBitmap.getUnderlyingBitmap()); if (!hasTransformableRotationAngle(closeableStaticBitmap) && !hasTransformableExifOrientation(closeableStaticBitmap)) { // Return the bitmap drawable directly as there's nothing to transform in it return bitmapDrawable; } } } finally { }}在createDrawable方法中，将获取到的缓存数据强转成CloseableStaticBitmap对象并执行getUnderlyingBitmap方法返回，实际就是就是一个Bitmap对象，再将其封装到BitmapDrawable对象，然后展示。
setImage最终调用在GenericDraweeHierarchy中：
//AbstractDraweeControllermSettableDraweeHierarchy.setImage(drawable, 1f, wasImmediate);//GenericDraweeHierarchy@Overridepublic void setImage(Drawable drawable, float progress, boolean immediate) { drawable = WrappingUtils.maybeApplyLeafRounding(drawable, mRoundingParams, mResources); drawable.mutate(); mActualImageWrapper.setDrawable(drawable); mFadeDrawable.beginBatchMode(); fadeOutBranches(); fadeInLayer(ACTUAL_IMAGE_INDEX); setProgress(progress); if (immediate) { mFadeDrawable.finishTransitionImmediately(); } mFadeDrawable.endBatchMode();}先看看有没有圆角参数需要设置，然后设置真正的位图，再渐变，设置进度，最后将刷新参数减一并统一刷新视图。
从attachController方法到现在只是讲了从缓存读取数据并展示，下面将以在线图片为例看看怎么加载图片的。
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