前言
成为一名优秀的Android开发，需要一份完备的知识体系，在这里，让我们一起成长为自己所想的那样~。
前两篇我们详细地分析了Android的网络底层框架OKHttp和封装框架Retrofit的核心源码，如果对OKHttp或Retrofit内部机制不了解的可以看看Android主流三方库源码分析（一、深入理解OKHttp源码）和Android主流三方库源码分析（二、深入理解Retrofit源码）。本篇，我们将会来深入地分析下目前Android使用最广泛的图片加载框架框架Glide的源码加载流程。
一、基本使用流程
Glide最基本的使用流程就是下面这行代码，其它所有扩展的额外功能都是以其建造者链式调用的基础上增加的。
GlideApp.with(context).load(url).into(iv);
其中的GlideApp是注解处理器自动生成的，要使用GlideApp，必须先配置应用的AppGlideModule模块，里面可以为空配置，也可以根据实际情况添加指定配置。
@GlideModule
public class MyAppGlideModule extends AppGlideModule {
@Override
public void applyOptions(Context context, GlideBuilder builder) {
// 实际使用中根据情况可以添加如下配置
<!--builder.setDefaultRequestOptions(new RequestOptions().format(DecodeFormat.PREFER_RGB_565));-->
<!--int memoryCacheSizeBytes = 1024 * 1024 * 20;-->
<!--builder.setMemoryCache(new LruResourceCache(memoryCacheSizeBytes));-->
<!--int bitmapPoolSizeBytes = 1024 * 1024 * 30;-->
<!--builder.setBitmapPool(new LruBitmapPool(bitmapPoolSizeBytes));-->
<!--int diskCacheSizeBytes = 1024 * 1024 * 100;-->
<!--builder.setDiskCache(new InternalCacheDiskCacheFactory(context, diskCacheSizeBytes));-->
}
}
接下来，本文将针对Glide的最新源码版本V4.8.0对Glide加载网络图片的流程进行详细地分析与讲解，力争做到让读者朋友们知其然也知其所以然。
二、GlideApp.with(context)源码详解
首先，用艽野尘梦绘制的这份Glide框架图让我们对Glide的总体框架有一个初步的了解。
从GlideApp.with这行代码开始，内部主线执行流程如下。
1、GlideApp#with
return (GlideRequests) Glide.with(context);
2、Glide#with
return getRetriever(context).get(context);
return Glide.get(context).getRequestManagerRetriever();
// 外部使用了双重检锁的同步方式确保同一时刻只执一次Glide的初始化
checkAndInitializeGlide(context);
initializeGlide(context);
// 最终执行到Glide的另一个重载方法
initializeGlide(context, new GlideBuilder());
@SuppressWarnings("deprecation")
private static void initializeGlide(@NonNull Context context, @NonNull GlideBuilder builder) {
Context applicationContext = context.getApplicationContext();
// 1、获取前面应用中带注解的GlideModule
GeneratedAppGlideModule annotationGeneratedModule = getAnnotationGeneratedGlideModules();
// 2、如果GlideModule为空或者可配置manifest里面的标志为true，则获取manifest里面
// 配置的GlideModule模块（manifestModules）。
List<com.bumptech.glide.module.GlideModule> manifestModules = Collections.emptyList();
if (annotationGeneratedModule == null || annotationGeneratedModule.isManifestParsingEnabled( )) {
manifestModules = new ManifestParser(applicationContext).parse();
}
...
RequestManagerRetriever.RequestManagerFactory factory =
annotationGeneratedModule != null
? annotationGeneratedModule.getRequestManag erFactory() : null;
builder.setRequestManagerFactory(factory);
for (com.bumptech.glide.module.GlideModule module : manifestModules) {
module.applyOptions(applicationContext, builder);
}
if (annotationGeneratedModule != null) {
annotationGeneratedModule.applyOptions(applicatio nContext, builder);
}
// 3、初始化各种配置信息
Glide glide = builder.build(applicationContext);
// 4、把manifestModules以及annotationGeneratedModule里面的配置信息放到builder
// 里面（applyOptions）替换glide默认组件（registerComponents）
for (com.bumptech.glide.module.GlideModule module : manifestModules) {
module.registerComponents(applicationContext, glide, glide.registry);
}
if (annotationGeneratedModule != null) {
annotationGeneratedModule.registerComponents(appl icationContext, glide, glide.registry);
}
applicationContext.registerComponentCallbacks(glide );
Glide.glide = glide;
}
3、GlideBuilder#build
@NonNull
Glide build(@NonNull Context context) {
// 创建请求图片线程池sourceExecutor
if (sourceExecutor == null) {
sourceExecutor = GlideExecutor.newSourceExecutor();
}
// 创建硬盘缓存线程池diskCacheExecutor
if (diskCacheExecutor == null) {
diskCacheExecutor = GlideExecutor.newDiskCacheExecutor();
}
// 创建动画线程池animationExecutor
if (animationExecutor == null) {
animationExecutor = GlideExecutor.newAnimationExecutor();
}
if (memorySizeCalculator == null) {
memorySizeCalculator = new MemorySizeCalculator.Builder(context).build();
}
if (connectivityMonitorFactory == null) {
connectivityMonitorFactory = new DefaultConnectivityMonitorFactory();
}
if (bitmapPool == null) {
// 依据设备的屏幕密度和尺寸设置各种pool的size
int size = memorySizeCalculator.getBitmapPoolSize();
if (size > 0) {
// 创建图片线程池LruBitmapPool，缓存所有被释放的bitmap
// 缓存策略在API大于19时，为SizeConfigStrategy，小于为AttributeStrategy。
// 其中SizeConfigStrategy是以bitmap的size和config为key，value为bitmap的HashMap
bitmapPool = new LruBitmapPool(size);
} else {
bitmapPool = new BitmapPoolAdapter();
}
}
// 创建对象数组缓存池LruArrayPool，默认4M
if (arrayPool == null) {
arrayPool = new LruArrayPool(memorySizeCalculator.getArrayPoolSiz eInBytes());
}
// 创建LruResourceCache，内存缓存
if (memoryCache == null) {
memoryCache = new LruResourceCache(memorySizeCalculator.getMemoryCa cheSize());
}
if (diskCacheFactory == null) {
diskCacheFactory = new InternalCacheDiskCacheFactory(context);
}
// 创建任务和资源管理引擎（线程池，内存缓存和硬盘缓存对象）
if (engine == null) {
engine =
new Engine(
memoryCache,
diskCacheFactory,
diskCacheExecutor,
sourceExecutor,
GlideExecutor.newUnlimitedSourceExecutor( ),
GlideExecutor.newAnimationExecutor(),
isActiveResourceRetentionAllowed);
}
RequestManagerRetriever requestManagerRetriever =
new RequestManagerRetriever(requestManagerFactory);
return new Glide(
context,
engine,
memoryCache,
bitmapPool,
arrayPool,
requestManagerRetriever,
connectivityMonitorFactory,
logLevel,
defaultRequestOptions.lock(),
defaultTransitionOptions);
}
4、Glide#Glide构造方法
Glide(...) {
...
// 注册管理任务执行对象的类(Registry)
// Registry是一个工厂，而其中所有注册的对象都是一个工厂员工，当任务分发时，
// 根据当前任务的性质，分发给相应员工进行处理
registry = new Registry();
...
// 这里大概有60余次的append或register员工组件（解析器、编解码器、工厂类、转码类等等组件）
registry
.append(ByteBuffer.class, new ByteBufferEncoder())
.append(InputStream.class, new StreamEncoder(arrayPool))
// 根据给定子类产出对应类型的target（BitmapImageViewTarget / DrawableImageViewTarget)
ImageViewTargetFactory imageViewTargetFactory = new ImageViewTargetFactory();
glideContext =
new GlideContext(
context,
arrayPool,
registry,
imageViewTargetFactory,
defaultRequestOptions,
defaultTransitionOptions,
engine,
logLevel);
}
5、RequestManagerRetriever#get
@NonNull
public RequestManager get(@NonNull Context context) {
if (context == null) {
throw new IllegalArgumentException("You cannot start a load on a null Context");
} else if (Util.isOnMainThread() && !(context instanceof Application)) {
// 如果当前线程是主线程且context不是Application走相应的get重载方法
if (context instanceof FragmentActivity) {
return get((FragmentActivity) context);
} else if (context instanceof Activity) {
return get((Activity) context);
} else if (context instanceof ContextWrapper) {
return get(((ContextWrapper) context).getBaseContext());
}
}
// 否则直接将请求与ApplicationLifecycle关联
return getApplicationManager(context);
}
这里总结一下，对于当前传入的context是application或当前线程是子线程时，请求的生命周期和ApplicationLifecycle关联，否则，context是FragmentActivity或Fragment时，在当前组件添加一个SupportFragment（SupportRequestManagerFragment），context是Activity时，在当前组件添加一个Fragment(RequestManagerFragment)。
6、GlideApp#with小结
1、初始化各式各样的配置信息（包括缓存，请求线程池，大小，图片格式等等）以及glide对象。
2、将glide请求和application/SupportFragment/Fragment的生命周期绑定在一块。
这里我们再回顾一下with方法的执行流程。
三、load(url)源码详解
1、GlideRequest(RequestManager)#load
return (GlideRequest<Drawable>) super.load(string);
return asDrawable().load(string);
// 1、asDrawable部分
return (GlideRequest<Drawable>) super.asDrawable();
return as(Drawable.class);
// 最终返回了一个GlideRequest（RequestManager的子类）
return new GlideRequest<>(glide, this, resourceClass, context);
// 2、load部分
return (GlideRequest<TranscodeType>) super.load(string);
return loadGeneric(string);
@NonNull
private RequestBuilder<TranscodeType> loadGeneric(@Nullable Object model) {
// model则为设置的url
this.model = model;
// 记录url已设置
isModelSet = true;
return this;
}
可以看到，load这部分的源码很简单，就是给GlideRequest（RequestManager）设置了要请求的mode（url），并记录了url已设置的状态。
这里，我们再看看load方法的执行流程。
四、into(iv)源码详解
前方预警，真正复杂的地方开始了。
1、RequestBuilder.into
@NonNull
public ViewTarget<ImageView, TranscodeType> into(@NonNull ImageView view) {
Util.assertMainThread();
Preconditions.checkNotNull(view);
RequestOptions requestOptions = this.requestOptions;
if (!requestOptions.isTransformationSet()
&& requestOptions.isTransformationAllowed()
&& view.getScaleType() != null) {
// Clone in this method so that if we use this RequestBuilder to load into a View and then
// into a different target, we don't retain the transformation applied based on the previous
// View's scale type.
switch (view.getScaleType()) {
// 这个RequestOptions里保存了要设置的scaleType，Glide自身封装了CenterCrop、CenterInside、
// FitCenter、CenterInside四种规格。
case CENTER_CROP:
requestOptions = requestOptions.clone().optionalCenterCrop();
break;
case CENTER_INSIDE:
requestOptions = requestOptions.clone().optionalCenterInside() ;
break;
case FIT_CENTER:
case FIT_START:
case FIT_END:
requestOptions = requestOptions.clone().optionalFitCenter();
break;
case FIT_XY:
requestOptions = requestOptions.clone().optionalCenterInside() ;
break;
case CENTER:
case MATRIX:
default:
// Do nothing.
}
}
// 注意，这个transcodeClass是指的drawable或bitmap
return into(
glideContext.buildImageViewTarget(view, transcodeClass),
/*targetListener=*/ null,
requestOptions);
}
2、GlideContext#buildImageViewTarget
return imageViewTargetFactory.buildTarget(imageView, transcodeClass);
3、ImageViewTargetFactory#buildTarget
@NonNull
@SuppressWarnings("unchecked")
public <Z> ViewTarget<ImageView, Z> buildTarget(@NonNull ImageView view,
@NonNull Class<Z> clazz) {
// 返回展示Bimtap/Drawable资源的目标对象
if (Bitmap.class.equals(clazz)) {
return (ViewTarget<ImageView, Z>) new BitmapImageViewTarget(view);
} else if (Drawable.class.isAssignableFrom(clazz)) {
return (ViewTarget<ImageView, Z>) new DrawableImageViewTarget(view);
} else {
throw new IllegalArgumentException(
"Unhandled class: " + clazz + ", try .as*(Class).transcode(ResourceTranscoder)");
}
}
可以看到，Glide内部只维护了两种target，一种是BitmapImageViewTarget，另一种则是DrawableImageViewTarget，接下来继续深入。
4、RequestBuilder#into
private <Y extends Target<TranscodeType>> Y into(
@NonNull Y target,
@Nullable RequestListener<TranscodeType> targetListener,
@NonNull RequestOptions options) {
Util.assertMainThread();
Preconditions.checkNotNull(target);
if (!isModelSet) {
throw new IllegalArgumentException("You must call #load() before calling #into()");
}
options = options.autoClone();
// 分析1.建立请求
Request request = buildRequest(target, targetListener, options);
Request previous = target.getRequest();
if (request.isEquivalentTo(previous)
&& !isSkipMemoryCacheWithCompletePreviousReques t(options, previous)) {
request.recycle();
// If the request is completed, beginning again will ensure the result is re-delivered,
// triggering RequestListeners and Targets. If the request is failed, beginning again will
// restart the request, giving it another chance to complete. If the request is already
// running, we can let it continue running without interruption.
if (!Preconditions.checkNotNull(previous).isRunni ng()) {
// Use the previous request rather than the new one to allow for optimizations like skipping
// setting placeholders, tracking and un-tracking Targets, and obtaining View dimensions
// that are done in the individual Request.
previous.begin();
}
return target;
}
requestManager.clear(target);
target.setRequest(request);
// 分析2.真正追踪请求的地方
requestManager.track(target, request);
return target;
}
// 分析1
private Request buildRequest(
Target<TranscodeType> target,
@Nullable RequestListener<TranscodeType> targetListener,
RequestOptions requestOptions) {
return buildRequestRecursive(
target,
targetListener,
/*parentCoordinator=*/ null,
transitionOptions,
requestOptions.getPriority(),
requestOptions.getOverrideWidth(),
requestOptions.getOverrideHeight(),
requestOptions);
}
// 分析1
private Request buildRequestRecursive(
Target<TranscodeType> target,
@Nullable RequestListener<TranscodeType> targetListener,
@Nullable RequestCoordinator parentCoordinator,
TransitionOptions<?, ? super TranscodeType> transitionOptions,
Priority priority,
int overrideWidth,
int overrideHeight,
RequestOptions requestOptions) {
// Build the ErrorRequestCoordinator first if necessary so we can update parentCoordinator.
ErrorRequestCoordinator errorRequestCoordinator = null;
if (errorBuilder != null) {
// 创建errorRequestCoordinator（异常处理对象）
errorRequestCoordinator = new ErrorRequestCoordinator(parentCoordinator);
parentCoordinator = errorRequestCoordinator;
}
// 递归建立缩略图请求
Request mainRequest =
buildThumbnailRequestRecursive(
target,
targetListener,
parentCoordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight,
requestOptions);
if (errorRequestCoordinator == null) {
return mainRequest;
}
...
Request errorRequest = errorBuilder.buildRequestRecursive(
target,
targetListener,
errorRequestCoordinator,
errorBuilder.transitionOptions,
errorBuilder.requestOptions.getPriority(),
errorOverrideWidth,
errorOverrideHeight,
errorBuilder.requestOptions);
errorRequestCoordinator.setRequests(mainRequest, errorRequest);
return errorRequestCoordinator;
}
// 分析1
private Request buildThumbnailRequestRecursive(
Target<TranscodeType> target,
RequestListener<TranscodeType> targetListener,
@Nullable RequestCoordinator parentCoordinator,
TransitionOptions<?, ? super TranscodeType> transitionOptions,
Priority priority,
int overrideWidth,
int overrideHeight,
RequestOptions requestOptions) {
if (thumbnailBuilder != null) {
// Recursive case: contains a potentially recursive thumbnail request builder.
...
ThumbnailRequestCoordinator coordinator = new ThumbnailRequestCoordinator(parentCoordinator);
// 获取一个正常请求对象
Request fullRequest =
obtainRequest(
target,
targetListener,
requestOptions,
coordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight);
isThumbnailBuilt = true;
// Recursively generate thumbnail requests.
// 使用递归的方式建立一个缩略图请求对象
Request thumbRequest =
thumbnailBuilder.buildRequestRecursive(
target,
targetListener,
coordinator,
thumbTransitionOptions,
thumbPriority,
thumbOverrideWidth,
thumbOverrideHeight,
thumbnailBuilder.requestOptions);
isThumbnailBuilt = false;
// coordinator（ThumbnailRequestCoordinator）是作为两者的协调者，
// 能够同时加载缩略图和正常的图的请求
coordinator.setRequests(fullRequest, thumbRequest);
return coordinator;
} else if (thumbSizeMultiplier != null) {
// Base case: thumbnail multiplier generates a thumbnail request, but cannot recurse.
// 当设置了缩略的比例thumbSizeMultiplier(0 ~ 1)时，
// 不需要递归建立缩略图请求
ThumbnailRequestCoordinator coordinator = new ThumbnailRequestCoordinator(parentCoordinator);
Request fullRequest =
obtainRequest(
target,
targetListener,
requestOptions,
coordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight);
RequestOptions thumbnailOptions = requestOptions.clone()
.sizeMultiplier(thumbSizeMultiplier);
Request thumbnailRequest =
obtainRequest(
target,
targetListener,
thumbnailOptions,
coordinator,
transitionOptions,
getThumbnailPriority(priority),
overrideWidth,
overrideHeight);
coordinator.setRequests(fullRequest, thumbnailRequest);
return coordinator;
} else {
// Base case: no thumbnail.
// 没有缩略图请求时，直接获取一个正常图请求
return obtainRequest(
target,
targetListener,
requestOptions,
parentCoordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight);
}
}
private Request obtainRequest(
Target<TranscodeType> target,
RequestListener<TranscodeType> targetListener,
RequestOptions requestOptions,
RequestCoordinator requestCoordinator,
TransitionOptions<?, ? super TranscodeType> transitionOptions,
Priority priority,
int overrideWidth,
int overrideHeight) {
// 最终实际返回的是一个SingleRequest对象（将制定的资源加载进对应的Target
return SingleRequest.obtain(
context,
glideContext,
model,
transcodeClass,
requestOptions,
overrideWidth,
overrideHeight,
priority,
target,
targetListener,
requestListeners,
requestCoordinator,
glideContext.getEngine(),
transitionOptions.getTransitionFactory());
}
从上源码分析可知，我们在分析1处的buildRequest()方法里建立了请求，且最多可同时进行缩略图和正常图的请求，最后，调用了requestManager.track(target, request)方法，接着看看track里面做了什么。
5、RequestManager#track
// 分析2
void track(@NonNull Target<?> target, @NonNull Request request) {
// 加入一个target目标集合(Set)
targetTracker.track(target);
requestTracker.runRequest(request);
}
6、RequestTracker#runRequest
/**
* Starts tracking the given request.
*/
// 分析2
public void runRequest(@NonNull Request request) {
requests.add(request);
if (!isPaused) {
// 如果不是暂停状态则开始请求
request.begin();
} else {
request.clear();
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Paused, delaying request");
}
// 否则清空请求，加入延迟请求队列（为了对这些请求维持一个强引用，使用了ArrayList实现）
pendingRequests.add(request);
}
}
7、SingleRequest#begin
// 分析2
@Override
public void begin() {
...
if (model == null) {
...
// model（url）为空，回调加载失败
onLoadFailed(new GlideException("Received null model"), logLevel);
return;
}
if (status == Status.RUNNING) {
throw new IllegalArgumentException("Cannot restart a running request");
}
if (status == Status.COMPLETE) {
onResourceReady(resource, DataSource.MEMORY_CACHE);
return;
}
status = Status.WAITING_FOR_SIZE;
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
// 当使用override() API为图片指定了一个固定的宽高时直接执行onSizeReady，
// 最终的核心处理位于onSizeReady
onSizeReady(overrideWidth, overrideHeight);
} else {
// 根据imageView的宽高算出图片的宽高，最终也会走到onSizeReady
target.getSize(this);
}
if ((status == Status.RUNNING || status == Status.WAITING_FOR_SIZE)
&& canNotifyStatusChanged()) {
// 预先加载设置的缩略图
target.onLoadStarted(getPlaceholderDrawable());
}
if (IS_VERBOSE_LOGGABLE) {
logV("finished run method in " + LogTime.getElapsedMillis(startTime));
}
}
从requestManager.track(target, request)开始，最终会执行到SingleRequest#begin()方法的onSizeReady，可以猜到（因为后面只做了预加载缩略图的处理），真正的请求就是从这里开始的，咱们进去一探究竟~
8、SingleRequest#onSizeReady
// 分析2
@Override
public void onSizeReady(int width, int height) {
stateVerifier.throwIfRecycled();
...
status = Status.RUNNING;
float sizeMultiplier = requestOptions.getSizeMultiplier();
this.width = maybeApplySizeMultiplier(width, sizeMultiplier);
this.height = maybeApplySizeMultiplier(height, sizeMultiplier);
...
// 根据给定的配置进行加载，engine是一个负责加载、管理活跃和缓存资源的引擎类
loadStatus = engine.load(
glideContext,
model,
requestOptions.getSignature(),
this.width,
this.height,
requestOptions.getResourceClass(),
transcodeClass,
priority,
requestOptions.getDiskCacheStrategy(),
requestOptions.getTransformations(),
requestOptions.isTransformationRequired(),
requestOptions.isScaleOnlyOrNoTransform(),
requestOptions.getOptions(),
requestOptions.isMemoryCacheable(),
requestOptions.getUseUnlimitedSourceGeneratorsP ool(),
requestOptions.getUseAnimationPool(),
requestOptions.getOnlyRetrieveFromCache(),
this);
...
}
终于看到Engine类了，感觉距离成功不远了，继续~
9、Engine#load
public <R> LoadStatus load(
GlideContext glideContext,
Object model,
Key signature,
int width,
int height,
Class<?> resourceClass,
Class<R> transcodeClass,
Priority priority,
DiskCacheStrategy diskCacheStrategy,
Map<Class<?>, Transformation<?>> transformations,
boolean isTransformationRequired,
boolean isScaleOnlyOrNoTransform,
Options options,
boolean isMemoryCacheable,
boolean useUnlimitedSourceExecutorPool,
boolean useAnimationPool,
boolean onlyRetrieveFromCache,
ResourceCallback cb) {
...
// 先从弱引用中查找，如果有的话回调onResourceReady并直接返回
EngineResource<?> active = loadFromActiveResources(key, isMemoryCacheable);
if (active != null) {
cb.onResourceReady(active, DataSource.MEMORY_CACHE);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Loaded resource from active resources", startTime, key);
}
return null;
}
// 没有再从内存中查找,有的话会取出并放到ActiveResources（内部维护的弱引用缓存map）里面
EngineResource<?> cached = loadFromCache(key, isMemoryCacheable);
if (cached != null) {
cb.onResourceReady(cached, DataSource.MEMORY_CACHE);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Loaded resource from cache", startTime, key);
}
return null;
}
EngineJob<?> current = jobs.get(key, onlyRetrieveFromCache);
if (current != null) {
current.addCallback(cb);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Added to existing load", startTime, key);
}
return new LoadStatus(cb, current);
}
// 如果内存中没有，则创建engineJob（decodejob的回调类，管理下载过程以及状态）
EngineJob<R> engineJob =
engineJobFactory.build(
key,
isMemoryCacheable,
useUnlimitedSourceExecutorPool,
useAnimationPool,
onlyRetrieveFromCache);
// 创建解析工作对象
DecodeJob<R> decodeJob =
decodeJobFactory.build(
glideContext,
model,
key,
signature,
width,
height,
resourceClass,
transcodeClass,
priority,
diskCacheStrategy,
transformations,
isTransformationRequired,
isScaleOnlyOrNoTransform,
onlyRetrieveFromCache,
options,
engineJob);
// 放在Jobs内部维护的HashMap中
jobs.put(key, engineJob);
// 关注点8 后面分析会用到
// 注册ResourceCallback接口
engineJob.addCallback(cb);
// 内部开启线程去请求
engineJob.start(decodeJob);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Started new load", startTime, key);
}
return new LoadStatus(cb, engineJob);
}
public void start(DecodeJob<R> decodeJob) {
this.decodeJob = decodeJob;
// willDecodeFromCache方法内部根据不同的阶段stage，如果是RESOURCE_CACHE/DATA_CACHE则返回true，使用diskCacheExecutor，否则调用getActiveSourceExecutor，内部会根据相应的条件返回sourceUnlimitedExecutor/animationExecutor/sourceExecutor
GlideExecutor executor =
decodeJob.willDecodeFromCache()
? diskCacheExecutor
: getActiveSourceExecutor();
executor.execute(decodeJob);
}
可以看到，最终Engine(引擎)类内部会执行到自身的start方法，它会根据不同的配置采用不同的线程池使用diskCacheExecutor/sourceUnlimitedExecutor/animationExecutor/sourceExecutor来执行最终的解码任务decodeJob。
10、DecodeJob#run
runWrapped();
private void runWrapped() {
switch (runReason) {
case INITIALIZE:
stage = getNextStage(Stage.INITIALIZE);
// 关注点1
currentGenerator = getNextGenerator();
// 关注点2 内部会调用相应Generator的startNext()
runGenerators();
break;
case SWITCH_TO_SOURCE_SERVICE:
runGenerators();
break;
case DECODE_DATA:
// 关注点3 将获取的数据解码成对应的资源
decodeFromRetrievedData();
break;
default:
throw new IllegalStateException("Unrecognized run reason: " + runReason);
}
}
// 关注点1，完整情况下，会异步依次生成这里的ResourceCacheGenerator、DataCacheGenerator和SourceGenerator对象，并在之后执行其中的startNext()
private DataFetcherGenerator getNextGenerator() {
switch (stage) {
case RESOURCE_CACHE:
return new ResourceCacheGenerator(decodeHelper, this);
case DATA_CACHE:
return new DataCacheGenerator(decodeHelper, this);
case SOURCE:
return new SourceGenerator(decodeHelper, this);
case FINISHED:
return null;
default:
throw new IllegalStateException("Unrecognized stage: " + stage);
}
}
11、SourceGenerator#startNext
// 关注点2
@Override
public boolean startNext() {
// dataToCache数据不为空的话缓存到硬盘（第一执行该方法是不会调用的）
if (dataToCache != null) {
Object data = dataToCache;
dataToCache = null;
cacheData(data);
}
if (sourceCacheGenerator != null && sourceCacheGenerator.startNext()) {
return true;
}
sourceCacheGenerator = null;
loadData = null;
boolean started = false;
while (!started && hasNextModelLoader()) {
// 关注点4 getLoadData()方法内部会在modelLoaders里面找到ModelLoder对象
// （每个Generator对应一个ModelLoader），
// 并使用modelLoader.buildLoadData方法返回一个loadData列表
loadData = helper.getLoadData().get(loadDataListIndex++);
if (loadData != null
&& (helper.getDiskCacheStrategy().isDataCache able(loadData.fetcher.getDataSource())
|| helper.hasLoadPath(loadData.fetcher.getDat aClass()))) {
started = true;
// 关注点6 通过loadData对象的fetcher对象（有关注点3的分析可知其实现类为HttpUrlFetcher）的
// loadData方法来获取图片数据
loadData.fetcher.loadData(helper.getPriority(), this);
}
}
return started;
}
12、DecodeHelper#getLoadData
List<LoadData<?>> getLoadData() {
if (!isLoadDataSet) {
isLoadDataSet = true;
loadData.clear();
List<ModelLoader<Object, ?>> modelLoaders = glideContext.getRegistry().getModelLoaders(model) ;
//noinspection ForLoopReplaceableByForEach to improve perf
for (int i = 0, size = modelLoaders.size(); i < size; i++) {
ModelLoader<Object, ?> modelLoader = modelLoaders.get(i);
// 注意：这里最终是通过HttpGlideUrlLoader的buildLoadData获取到实际的loadData对象
LoadData<?> current =
modelLoader.buildLoadData(model, width, height, options);
if (current != null) {
loadData.add(current);
}
}
}
return loadData;
}
13、HttpGlideUrlLoader#buildLoadData
@Override
public LoadData<InputStream> buildLoadData(@NonNull GlideUrl model, int width, int height,
@NonNull Options options) {
// GlideUrls memoize parsed URLs so caching them saves a few object instantiations and time
// spent parsing urls.
GlideUrl url = model;
if (modelCache != null) {
url = modelCache.get(model, 0, 0);
if (url == null) {
// 关注点5
modelCache.put(model, 0, 0, model);
url = model;
}
}
int timeout = options.get(TIMEOUT);
// 注意，这里创建了一个DataFetcher的实现类HttpUrlFetcher
return new LoadData<>(url, new HttpUrlFetcher(url, timeout));
}
// 关注点5
public void put(A model, int width, int height, B value) {
ModelKey<A> key = ModelKey.get(model, width, height);
// 最终是通过LruCache来缓存对应的值，key是一个ModelKey对象（由model、width、height三个属性组成）
cache.put(key, value);
}
从这里的分析，我们明白了HttpUrlFetcher实际上就是最终的请求执行者，而且，我们知道了Glide会使用LruCache来对解析后的url来进行缓存，以便后续可以省去解析url的时间。
14、HttpUrlFetcher#loadData
@Override
public void loadData(@NonNull Priority priority,
@NonNull DataCallback<? super InputStream> callback) {
long startTime = LogTime.getLogTime();
try {
// 关注点6
// loadDataWithRedirects内部是通过HttpURLConnection网络请求数据
InputStream result = loadDataWithRedirects(glideUrl.toURL(), 0, null, glideUrl.getHeaders());
// 请求成功回调onDataReady()
callback.onDataReady(result);
} catch (IOException e) {
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(TAG, "Failed to load data for url", e);
}
callback.onLoadFailed(e);
} finally {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Finished http url fetcher fetch in " + LogTime.getElapsedMillis(startTime));
}
}
}
private InputStream loadDataWithRedirects(URL url, int redirects, URL lastUrl,
Map<String, String> headers) throws IOException {
...
urlConnection.connect();
// Set the stream so that it's closed in cleanup to avoid resource leaks. See #2352.
stream = urlConnection.getInputStream();
if (isCancelled) {
return null;
}
final int statusCode = urlConnection.getResponseCode();
// 只要是2xx形式的状态码则判断为成功
if (isHttpOk(statusCode)) {
// 从urlConnection中获取资源流
return getStreamForSuccessfulRequest(urlConnection);
} else if (isHttpRedirect(statusCode)) {
...
// 重定向请求
return loadDataWithRedirects(redirectUrl, redirects + 1, url, headers);
} else if (statusCode == INVALID_STATUS_CODE) {
throw new HttpException(statusCode);
} else {
throw new HttpException(urlConnection.getResponseMessage(), statusCode);
}
}
private InputStream getStreamForSuccessfulRequest(HttpURLConnection urlConnection)
throws IOException {
if (TextUtils.isEmpty(urlConnection.getContentEncoding())) {
int contentLength = urlConnection.getContentLength();
stream = ContentLengthInputStream.obtain(urlConnection.getInputStr eam(), contentLength);
} else {
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(TAG, "Got non empty content encoding: " + urlConnection.getContentEncoding());
}
stream = urlConnection.getInputStream();
}
return stream;
}
在HttpUrlFetcher#loadData方法的loadDataWithRedirects里面，Glide通过原生的HttpURLConnection进行请求后，并调用getStreamForSuccessfulRequest()方法获取到了最终的图片流。
15、DecodeJob#run
在我们通过HtttpUrlFetcher的loadData()方法请求得到对应的流之后，我们还必须对流进行处理得到最终我们想要的资源。这里我们回到第10步DecodeJob#run方法的关注点3处，这行代码将会对流进行解码。
decodeFromRetrievedData();
接下来，继续看看他内部的处理。
private void decodeFromRetrievedData() {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Retrieved data", startFetchTime,
"data: " + currentData
+ ", cache key: " + currentSourceKey
+ ", fetcher: " + currentFetcher);
}
Resource<R> resource = null;
try {
// 核心代码
// 从数据中解码得到资源
resource = decodeFromData(currentFetcher, currentData, currentDataSource);
} catch (GlideException e) {
e.setLoggingDetails(currentAttemptingKey, currentDataSource);
throwables.add(e);
}
if (resource != null) {
// 关注点8
// 编码和发布最终得到的Resource<Bitmap>对象
notifyEncodeAndRelease(resource, currentDataSource);
} else {
runGenerators();
}
}
private <Data> Resource<R> decodeFromData(DataFetcher<?> fetcher, Data data,
DataSource dataSource) throws GlideException {
try {
if (data == null) {
return null;
}
long startTime = LogTime.getLogTime();
// 核心代码
// 进一步包装了解码方法
Resource<R> result = decodeFromFetcher(data, dataSource);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Decoded result " + result, startTime);
}
return result;
} finally {
fetcher.cleanup();
}
}
@SuppressWarnings("unchecked")
private <Data> Resource<R> decodeFromFetcher(Data data, DataSource dataSource)
throws GlideException {
LoadPath<Data, ?, R> path = decodeHelper.getLoadPath((Class<Data>) data.getClass());
// 核心代码
// 将解码任务分发给LoadPath
return runLoadPath(data, dataSource, path);
}
private <Data, ResourceType> Resource<R> runLoadPath(Data data, DataSource dataSource,
LoadPath<Data, ResourceType, R> path) throws GlideException {
Options options = getOptionsWithHardwareConfig(dataSource);
// 将数据进一步包装
DataRewinder<Data> rewinder = glideContext.getRegistry().getRewinder(data);
try {
// ResourceType in DecodeCallback below is required for compilation to work with gradle.
// 核心代码
// 将解码任务分发给LoadPath
return path.load(
rewinder, options, width, height, new DecodeCallback<ResourceType>(dataSource));
} finally {
rewinder.cleanup();
}
}
16、LoadPath#load
public Resource<Transcode> load(DataRewinder<Data> rewinder, @NonNull Options options, int width,
int height, DecodePath.DecodeCallback<ResourceType> decodeCallback) throws GlideException {
List<Throwable> throwables = Preconditions.checkNotNull(listPool.acquire());
try {
// 核心代码
return loadWithExceptionList(rewinder, options, width, height, decodeCallback, throwables);
} finally {
listPool.release(throwables);
}
}
private Resource<Transcode> loadWithExceptionList(DataRewinder<Data> rewinder,
@NonNull Options options,
int width, int height, DecodePath.DecodeCallback<ResourceType> decodeCallback,
List<Throwable> exceptions) throws GlideException {
Resource<Transcode> result = null;
//noinspection ForLoopReplaceableByForEach to improve perf
for (int i = 0, size = decodePaths.size(); i < size; i++) {
DecodePath<Data, ResourceType, Transcode> path = decodePaths.get(i);
try {
// 核心代码
// 将解码任务又进一步分发给DecodePath的decode方法去解码
result = path.decode(rewinder, width, height, options, decodeCallback);
} catch (GlideException e) {
exceptions.add(e);
}
if (result != null) {
break;
}
}
if (result == null) {
throw new GlideException(failureMessage, new ArrayList<>(exceptions));
}
return result;
}
17、DecodePath#decode
public Resource<Transcode> decode(DataRewinder<DataType> rewinder, int width, int height,
@NonNull Options options, DecodeCallback<ResourceType> callback) throws GlideException {
// 核心代码
// 继续调用DecodePath的decodeResource方法去解析出数据
Resource<ResourceType> decoded = decodeResource(rewinder, width, height, options);
Resource<ResourceType> transformed = callback.onResourceDecoded(decoded);
return transcoder.transcode(transformed, options);
}
@NonNull
private Resource<ResourceType> decodeResource(DataRewinder<DataType> rewinder, int width,
int height, @NonNull Options options) throws GlideException {
List<Throwable> exceptions = Preconditions.checkNotNull(listPool.acquire());
try {
// 核心代码
return decodeResourceWithList(rewinder, width, height, options, exceptions);
} finally {
listPool.release(exceptions);
}
}
@NonNull
private Resource<ResourceType> decodeResourceWithList(DataRewinder<DataType> rewinder, int width,
int height, @NonNull Options options, List<Throwable> exceptions) throws GlideException {
Resource<ResourceType> result = null;
//noinspection ForLoopReplaceableByForEach to improve perf
for (int i = 0, size = decoders.size(); i < size; i++) {
ResourceDecoder<DataType, ResourceType> decoder = decoders.get(i);
try {
DataType data = rewinder.rewindAndGet();
if (decoder.handles(data, options)) {
// 获取包装的数据
data = rewinder.rewindAndGet();
// 核心代码
// 根据DataType和ResourceType的类型分发给不同的解码器Decoder
result = decoder.decode(data, width, height, options);
}
} catch (IOException | RuntimeException | OutOfMemoryError e) {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Failed to decode data for " + decoder, e);
}
exceptions.add(e);
}
if (result != null) {
break;
}
}
if (result == null) {
throw new GlideException(failureMessage, new ArrayList<>(exceptions));
}
return result;
}
可以看到，经过一连串的嵌套调用，最终执行到了decoder.decode()这行代码，decode是一个ResourceDecoder
18、ByteBufferBitmapDecoder#decode
/**
* Decodes {@link android.graphics.Bitmap Bitmaps} from {@link java.nio.ByteBuffer ByteBuffers}.
*/
public class ByteBufferBitmapDecoder implements ResourceDecoder<ByteBuffer, Bitmap> {
...
@Override
public Resource<Bitmap> decode(@NonNull ByteBuffer source, int width, int height,
@NonNull Options options)
throws IOException {
InputStream is = ByteBufferUtil.toStream(source);
// 核心代码
return downsampler.decode(is, width, height, options);
}
}
可以看到，最终是使用了一个downsampler，它是一个压缩器，主要是对流进行解码，压缩，圆角等处理。
19、DownSampler#decode
public Resource<Bitmap> decode(InputStream is, int outWidth, int outHeight,
Options options) throws IOException {
return decode(is, outWidth, outHeight, options, EMPTY_CALLBACKS);
}
@SuppressWarnings({"resource", "deprecation"})
public Resource<Bitmap> decode(InputStream is, int requestedWidth, int requestedHeight,
Options options, DecodeCallbacks callbacks) throws IOException {
Preconditions.checkArgument(is.markSupported(), "You must provide an InputStream that supports"
+ " mark()");
...
try {
// 核心代码
Bitmap result = decodeFromWrappedStreams(is, bitmapFactoryOptions,
downsampleStrategy, decodeFormat, isHardwareConfigAllowed, requestedWidth,
requestedHeight, fixBitmapToRequestedDimensions, callbacks);
// 关注点7
// 解码得到Bitmap对象后，包装成BitmapResource对象返回，
// 通过内部的get方法得到Resource<Bitmap>对象
return BitmapResource.obtain(result, bitmapPool);
} finally {
releaseOptions(bitmapFactoryOptions);
byteArrayPool.put(bytesForOptions);
}
}
private Bitmap decodeFromWrappedStreams(InputStream is,
BitmapFactory.Options options, DownsampleStrategy downsampleStrategy,
DecodeFormat decodeFormat, boolean isHardwareConfigAllowed, int requestedWidth,
int requestedHeight, boolean fixBitmapToRequestedDimensions,
DecodeCallbacks callbacks) throws IOException {
// 省去计算压缩比例等一系列非核心逻辑
...
// 核心代码
Bitmap downsampled = decodeStream(is, options, callbacks, bitmapPool);
callbacks.onDecodeComplete(bitmapPool, downsampled);
...
// Bimtap旋转处理
...
return rotated;
}
private static Bitmap decodeStream(InputStream is, BitmapFactory.Options options,
DecodeCallbacks callbacks, BitmapPool bitmapPool) throws IOException {
...
TransformationUtils.getBitmapDrawableLock().lock();
try {
// 核心代码
result = BitmapFactory.decodeStream(is, null, options);
} catch (IllegalArgumentException e) {
...
} finally {
TransformationUtils.getBitmapDrawableLock().unlock();
}
if (options.inJustDecodeBounds) {
is.reset();
}
return result;
}
从以上源码流程我们知道，最后是在DownSampler的decodeStream()方法中使用了BitmapFactory.decodeStream()来得到Bitmap对象。然后，我们来分析下图片时如何显示的，我们回到步骤19的DownSampler#decode方法，看到关注点7，这里是将Bitmap包装成BitmapResource对象返回，通过内部的get方法可以得到Resource
20、DecodeJob#notifyEncodeAndRelease
private void notifyEncodeAndRelease(Resource<R> resource, DataSource dataSource) {
...
notifyComplete(result, dataSource);
...
}
private void notifyComplete(Resource<R> resource, DataSource dataSource) {
setNotifiedOrThrow();
callback.onResourceReady(resource, dataSource);
}
从以上EngineJob的源码可知，它实现了DecodeJob.CallBack
class EngineJob<R> implements DecodeJob.Callback<R>,
Poolable {
...
}
21、EngineJob#onResourceReady
@Override
public void onResourceReady(Resource<R> resource, DataSource dataSource) {
this.resource = resource;
this.dataSource = dataSource;
MAIN_THREAD_HANDLER.obtainMessage(MSG_COMPLETE, this).sendToTarget();
}
private static class MainThreadCallback implements Handler.Callback{
...
@Override
public boolean handleMessage(Message message) {
EngineJob<?> job = (EngineJob<?>) message.obj;
switch (message.what) {
case MSG_COMPLETE:
// 核心代码
job.handleResultOnMainThread();
break;
...
}
return true;
}
}
从以上源码可知，通过主线程Handler对象进行切换线程，然后在主线程调用了handleResultOnMainThread这个方法。
@Synthetic
void handleResultOnMainThread() {
...
//noinspection ForLoopReplaceableByForEach to improve perf
for (int i = 0, size = cbs.size(); i < size; i++) {
ResourceCallback cb = cbs.get(i);
if (!isInIgnoredCallbacks(cb)) {
engineResource.acquire();
cb.onResourceReady(engineResource, dataSource);
}
}
...
}
这里又通过一个循环调用了所有ResourceCallback的方法，让我们回到步骤9处Engine#load方法的关注点8这行代码，这里对ResourceCallback进行了注册，在步骤8出SingleRequest#onSizeReady方法里的engine.load中，我们看到最后一个参数，传入的是this，可以明白，engineJob.addCallback(cb)这里的cb的实现类就是SingleRequest。接下来，让我们看看SingleRequest的onResourceReady方法。
22、SingleRequest#onResourceReady
/**
* A callback method that should never be invoked directly.
*/
@SuppressWarnings("unchecked")
@Override
public void onResourceReady(Resource<?> resource, DataSource dataSource) {
...
// 从Resource<Bitmap>中得到Bitmap对象
Object received = resource.get();
...
onResourceReady((Resource<R>) resource, (R) received, dataSource);
}
private void onResourceReady(Resource<R> resource, R resultDataSource dataSource) {
...
try {
...
if (!anyListenerHandledUpdatingTarget) {
Transition<? super R> animation =
animationFactory.build(dataSource, isFirstResource);
// 核心代码
target.onResourceReady(result, animation);
}
} finally {
isCallingCallbacks = false;
}
notifyLoadSuccess();
}
在SingleRequest#onResourceReady方法中又调用了target.onResourceReady(result, animation)方法，这里的target其实就是我们在into方法中建立的那个BitmapImageViewTarget，看到ImageViewTarget类，我们并没有发现onResourceReady方法，但是我们从它的子类ImageViewTarget中发现了onResourceReady方法，从这里我们继续往下看。
23、ImageViewTarget#onResourceReady
public abstract class ImageViewTarget<Z> extends ViewTarget<ImageView, Z>
implements Transition.ViewAdapter {
...
@Override
public void onResourceReady(@NonNull Z resource, @Nullable Transition<? super Z> transition) {
if (transition == null || !transition.transition(resource, this)) {
// 核心代码
setResourceInternal(resource);
} else {
maybeUpdateAnimatable(resource);
}
}
...
private void setResourceInternal(@Nullable Z resource) {
// Order matters here. Set the resource first to make sure that the Drawable has a valid and
// non-null Callback before starting it.
// 核心代码
setResource(resource);
maybeUpdateAnimatable(resource);
}
// 核心代码
protected abstract void setResource(@Nullable Z resource);
}
这里我们在回到BitmapImageViewTarget的setResource方法中，我们终于看到Bitmap被设置到了当前的imageView上了。
public class BitmapImageViewTarget extends ImageViewTarget<Bitmap> {
...
@Override
protected void setResource(Bitmap resource) {
view.setImageBitmap(resource);
}
}
到这里，我们的分析就结束了，从以上的分析可知，Glide将大部分的逻辑处理都放在了最后一个into方法中，里面经过了20多个分析步骤才将请求图片流、解码出图片，到最终设置到对应的imageView上。
最后，这里给出一份我花费了数个小时绘制的完整Glide加载流程图，非常珍贵，大家可以仔仔细细再把Glide的主体流程在梳理一遍。
五、总结
到此，Glide整个的加载流程分析就结束了，可以看到，Glide最核心的逻辑都聚集在into()方法中，它里面的设计精巧而复杂，这部分的源码分析非常耗时，但是，如果你真真正正地去一步步去深入其中，你也许在Android进阶之路上将会有顿悟的感觉。目前，Android主流三方库源码分析系列已经对网络库（OkHttp、Retrofit）和图片加载库（Glide）进行了详细的源码分析，接下来，将会对数据库框架GreenDao的核心源码进行深入的分析，敬请期待~
参考链接：
1、Glide V4.8.0源码
赞赏
如果这个库对您有很大帮助，您愿意支持这个项目的进一步开发和这个项目的持续维护。你可以扫描下面的二维码，让我喝一杯咖啡或啤酒。非常感谢您的捐赠。谢谢！
Contanct Me
● 微信：
欢迎关注我的微信：
bcce5360
● 微信群：
微信群如果不能扫码加入，麻烦大家想进微信群的朋友们，加我微信拉你进群。
● QQ群：
2千人QQ群，Awesome-Android学习交流群，QQ群号：959936182， 欢迎大家加入~
About me
Email: chao.qu521@gmail.com
Blog: https://jsonchao.github.io/
掘金: https://juejin.im/user/5a3ba9375188252bca050ade
