Glide源码解析二---into方法
转载请标明出处，维权必究： https://www.cnblogs.com/tangZH/p/12543154.htmlGlide作为一个强大的图片加载框架，已经被android官方使用，所以，明白Glide的加载流程以及原理对加深我们对glide的理解是很重要的。
本文基于glide 4.11
Glide.with(this).load("").into(new ImageView(this));我们从这一句入手，上次我们看了Glide的初始化过程，也就是Glide.with(this)这个方法。现在我们来看into方法。
@NonNull
public ViewTarget<ImageView, TranscodeType> into(@NonNull ImageView view) {
Util.assertMainThread();
//检查view是否为null
Preconditions.checkNotNull(view);
//根据view.getScaleType()设置不同的transform变换，这个transform变换我们单独讲
BaseRequestOptions<?> requestOptions = this;
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()) {
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.
}
}
return into(
//根据transcodeClass的类型构造不同的Target
glideContext.buildImageViewTarget(view, transcodeClass),
/*targetListener=*/ null,
requestOptions,
Executors.mainThreadExecutor());
}构建不同的target
glideContext.buildImageViewTarget(view, transcodeClass)，跟着代码点进去，最后跟踪到了这里：
public <Z> ViewTarget<ImageView, Z> buildTarget(
@NonNull ImageView view, @NonNull Class<Z> clazz) {
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)");
}
}如果说我们最终要将资源解码为bitmap，那么就构造BitmapImageViewTarget，如果要将资源解码为Drawable，那么就构造DrawableImageViewTarget。
如果你在使用Glide加载图片的时候调用了asBitmap()方法，那么这里就会构建出BitmapImageViewTarget对象，否则的话构建的都是DrawableImageViewTarget对象。
target里面有一些方法，比如失败的回调，设置资源等等。
接下来继续看代码，会调用下面这个方法。
private <Y extends Target<TranscodeType>> Y into(
@NonNull Y target,
@Nullable RequestListener<TranscodeType> targetListener,
BaseRequestOptions<?> options,
Executor callbackExecutor) {
Preconditions.checkNotNull(target);
//检测是否已经调用过load方法
if (!isModelSet) {
throw new IllegalArgumentException("You must call #load() before calling #into()");
}
//构造request
Request request = buildRequest(target, targetListener, options, callbackExecutor);
//获取改target是否已经有绑定的request
Request previous = target.getRequest();
/**
* 这里修复了一个bug，详见 https://github.com/bumptech/glide/issues/2270
*/
if (request.isEquivalentTo(previous)
&& !isSkipMemoryCacheWithCompletePreviousRequest(options, previous)) {
// 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).isRunning()) {
// 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);
//将该request设置给target
target.setRequest(request);
requestManager.track(target, request);
return target;
}先看一下buildRequest(target, targetListener, options, callbackExecutor);做了什么
追踪进去，调用buildRequestRecursive方法。
然后主要是这两个方法：
Request mainRequest =
buildThumbnailRequestRecursive(
requestLock,
target,
targetListener,
parentCoordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight,
requestOptions,
callbackExecutor);
Request errorRequest =
errorBuilder.buildRequestRecursive(
requestLock,
target,
targetListener,
errorRequestCoordinator,
errorBuilder.transitionOptions,
errorBuilder.getPriority(),
errorOverrideWidth,
errorOverrideHeight,
errorBuilder,
callbackExecutor);最后设置给ErrorRequestCoordinator
errorRequestCoordinator.setRequests(mainRequest, errorRequest);
ErrorRequestCoordinator负责管理这些请求，如果请求失败就运行错误的请求。
我们看这个方法：buildThumbnailRequestRecursive
private Request buildThumbnailRequestRecursive(
Object requestLock,
Target<TranscodeType> target,
RequestListener<TranscodeType> targetListener,
@Nullable RequestCoordinator parentCoordinator,
TransitionOptions<?, ? super TranscodeType> transitionOptions,
Priority priority,
int overrideWidth,
int overrideHeight,
BaseRequestOptions<?> requestOptions,
Executor callbackExecutor) {
if (thumbnailBuilder != null) {
// Recursive case: contains a potentially recursive thumbnail request builder.
if (isThumbnailBuilt) {
throw new IllegalStateException(
"You cannot use a request as both the main request and a "
+ "thumbnail, consider using clone() on the request(s) passed to thumbnail()");
}
TransitionOptions<?, ? super TranscodeType> thumbTransitionOptions =
thumbnailBuilder.transitionOptions;
// Apply our transition by default to thumbnail requests but avoid overriding custom options
// that may have been applied on the thumbnail request explicitly.
if (thumbnailBuilder.isDefaultTransitionOptionsSet) {
thumbTransitionOptions = transitionOptions;
}
Priority thumbPriority =
thumbnailBuilder.isPrioritySet()
? thumbnailBuilder.getPriority()
: getThumbnailPriority(priority);
int thumbOverrideWidth = thumbnailBuilder.getOverrideWidth();
int thumbOverrideHeight = thumbnailBuilder.getOverrideHeight();
if (Util.isValidDimensions(overrideWidth, overrideHeight)
&& !thumbnailBuilder.isValidOverride()) {
thumbOverrideWidth = requestOptions.getOverrideWidth();
thumbOverrideHeight = requestOptions.getOverrideHeight();
}
ThumbnailRequestCoordinator coordinator =
new ThumbnailRequestCoordinator(requestLock, parentCoordinator);
Request fullRequest =
obtainRequest(
requestLock,
target,
targetListener,
requestOptions,
coordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight,
callbackExecutor);
isThumbnailBuilt = true;
// Recursively generate thumbnail requests.
Request thumbRequest =
thumbnailBuilder.buildRequestRecursive(
requestLock,
target,
targetListener,
coordinator,
thumbTransitionOptions,
thumbPriority,
thumbOverrideWidth,
thumbOverrideHeight,
thumbnailBuilder,
callbackExecutor);
isThumbnailBuilt = false;
coordinator.setRequests(fullRequest, thumbRequest);
return coordinator;
} else if (thumbSizeMultiplier != null) {
// Base case: thumbnail multiplier generates a thumbnail request, but cannot recurse.
ThumbnailRequestCoordinator coordinator =
new ThumbnailRequestCoordinator(requestLock, parentCoordinator);
Request fullRequest =
obtainRequest(
requestLock,
target,
targetListener,
requestOptions,
coordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight,
callbackExecutor);
BaseRequestOptions<?> thumbnailOptions =
requestOptions.clone().sizeMultiplier(thumbSizeMultiplier);
Request thumbnailRequest =
obtainRequest(
requestLock,
target,
targetListener,
thumbnailOptions,
coordinator,
transitionOptions,
getThumbnailPriority(priority),
overrideWidth,
overrideHeight,
callbackExecutor);
coordinator.setRequests(fullRequest, thumbnailRequest);
return coordinator;
} else {
// Base case: no thumbnail.
return obtainRequest(
requestLock,
target,
targetListener,
requestOptions,
parentCoordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight,
callbackExecutor);
}
}首先对缩略图及是否对Target设置参数的判断(是否使用了thumbnail()方法和sizeMultiplier()方法)，如果有使用thunmnail()方法，则生成原始图片和缩略图的请求，并由ThumbnailRequestCoordinator对象来协调管理，使用了sizeMultiplier()方法，则同样的处理(前者递归的获得缩略图的Request，后者不递归)，否则就只生成原始图片的请求。
他们最终都会调用obtainRequest方法，追踪进去可以发现该方法最终返回的是SingleRequest对象。初始化request的时候传递的参数很多：
public static <R> SingleRequest<R> obtain(
Context context,
GlideContext glideContext,
Object requestLock,
Object model,
Class<R> transcodeClass,
BaseRequestOptions<?> requestOptions,
int overrideWidth,
int overrideHeight,
Priority priority,
Target<R> target,
RequestListener<R> targetListener,
@Nullable List<RequestListener<R>> requestListeners,
RequestCoordinator requestCoordinator,
Engine engine,
TransitionFactory<? super R> animationFactory,
Executor callbackExecutor) {1.GlideContext glideContext : 全局上下文
2.Object model ：加载的资源类型
3.Class transcodeClass ：转换的类型
4.RequestOptions requestOptions：设置选项（包括：skipMemoryCache，errorDrawable，placeholder，timeoutOf，encodeFormatOf等等）
5.int overrideWidth：目标宽度在所需资源的像素点。
6.int overrideHeight：目标高度在所需资源的像素点。
7. Priority priority：加载的优先级（IMMEDIATE,HIGH,NORMAL,LOW）
8.Target target:上面刚讲过，绑定的target
9.RequestListener requestListener:请求加载时候的监听器
10.RequestCoordinator requestCoordinator:请求协调器（用来协调具有相同Target的协调器）
11.Engine engine:负责启动负载和管理活动和缓存资源。
12.TransitionFactory<? super R> animationFactory:一个工厂类，可以根据请求的状态产生不同的转换。
我们再回到into代码中，获取了request之后我们就要开始请求了。
我们看着一句requestManager.track(target, request);
synchronized void track(@NonNull Target<?> target, @NonNull Request request) {
targetTracker.track(target);
requestTracker.runRequest(request);
}runRequest就是执行请求的代码：
/** Starts tracking the given request. */
public void runRequest(@NonNull Request request) {
requests.add(request);
if (!isPaused) {
request.begin();
} else {
request.clear();
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Paused, delaying request");
}
pendingRequests.add(request);
}
}判断Glide当前是不是处理暂停状态，如果不是暂停状态就调用Request的begin()方法来执行Request，否则的话就先将Request添加到待执行队列里面，等暂停状态解除了之后再执行。
我们来看begin方法：
@Override
public void begin() {
synchronized (requestLock) {
assertNotCallingCallbacks();
stateVerifier.throwIfRecycled();
startTime = LogTime.getLogTime();
if (model == null) {
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
width = overrideWidth;
height = overrideHeight;
}
// Only log at more verbose log levels if the user has set a fallback drawable, because
// fallback Drawables indicate the user expects null models occasionally.
int logLevel = getFallbackDrawable() == null ? Log.WARN : Log.DEBUG;
onLoadFailed(new GlideException("Received null model"), logLevel);
return;
}
if (status == Status.RUNNING) {
throw new IllegalArgumentException("Cannot restart a running request");
}
如果说这个资源已经被加载过了，那么我们直接调用onResourceReady
// If we're restarted after we're complete (usually via something like a notifyDataSetChanged
// that starts an identical request into the same Target or View), we can simply use the
// resource and size we retrieved the last time around and skip obtaining a new size, starting
// a new load etc. This does mean that users who want to restart a load because they expect
// that the view size has changed will need to explicitly clear the View or Target before
// starting the new load.
if (status == Status.COMPLETE) {
onResourceReady(resource, DataSource.MEMORY_CACHE);
return;
}
// Restarts for requests that are neither complete nor running can be treated as new requests
// and can run again from the beginning.
status = Status.WAITING_FOR_SIZE;
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
onSizeReady(overrideWidth, overrideHeight);
} else {
target.getSize(this);
}
if ((status == Status.RUNNING || status == Status.WAITING_FOR_SIZE)
&& canNotifyStatusChanged()) {
target.onLoadStarted(getPlaceholderDrawable());
}
if (IS_VERBOSE_LOGGABLE) {
logV("finished run method in " + LogTime.getElapsedMillis(startTime));
}
}
}如果model为null，说明我们没有调用load方法，这时候会回调onLoadFailed，将status设置为Status.FAILED，然后调用setErrorPlaceholder，这个方法里面最终调用target.onLoadFailed(error);将资源置空，然后显示错误图片。
@Override
public void begin() {
synchronized (requestLock) {
assertNotCallingCallbacks();
stateVerifier.throwIfRecycled();
startTime = LogTime.getLogTime();
if (model == null) {
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
width = overrideWidth;
height = overrideHeight;
}
// Only log at more verbose log levels if the user has set a fallback drawable, because
// fallback Drawables indicate the user expects null models occasionally.
int logLevel = getFallbackDrawable() == null ? Log.WARN : Log.DEBUG;
onLoadFailed(new GlideException("Received null model"), logLevel);
return;
}
if (status == SingleRequest.Status.RUNNING) {
throw new IllegalArgumentException("Cannot restart a running request");
}
/**
* 如果完成后重新启动（通常是通过notifyDataSetChanged之类的方法
* 将相同的请求发送到相同的Target或View），我们可以简单地使用
* 我们最后一次检索的资源和大小，然后跳过获取新大小的步骤，
* 不用开始一个新的加载。这确实意味着要重新加载的用户，因为他们
* 更改视图大小，那么需要先明确清除view和target，然后
* 开始新的加载。
*/
if (status == SingleRequest.Status.COMPLETE) {
onResourceReady(resource, DataSource.MEMORY_CACHE);
return;
}
// Restarts for requests that are neither complete nor running can be treated as new requests
// and can run again from the beginning.
status = SingleRequest.Status.WAITING_FOR_SIZE;
/**
* 这里会判断Util.isValidDimensions(overrideWidth, overrideHeight)
* 如果你在使用时候调用了override() API为图片指定了一个固定的宽高，就会按照你给定的去加载；第二种情况是没有给定的情况，
* 那么target.getSize()方法的内部会根据ImageView的layout_width和layout_height值做一系列的计算，来算出图片应该的宽高，
* 具体计算就在getSize里面
* 但是不管怎样，最后都会调用onSizeReady()。
*/
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
onSizeReady(overrideWidth, overrideHeight);
} else {
target.getSize(this);
}
if ((status == SingleRequest.Status.RUNNING || status == SingleRequest.Status.WAITING_FOR_SIZE)
&& canNotifyStatusChanged()) {
target.onLoadStarted(getPlaceholderDrawable());
}
if (IS_VERBOSE_LOGGABLE) {
logV("finished run method in " + LogTime.getElapsedMillis(startTime));
}
}
}我们进去onSizeReady看看
@Override
public void onSizeReady(int width, int height) {
//如果对象以及被回收了，那么抛出异常
stateVerifier.throwIfRecycled();
synchronized (requestLock) {
if (IS_VERBOSE_LOGGABLE) {
logV("Got onSizeReady in " + LogTime.getElapsedMillis(startTime));
}
//说明没有设置大小或者没有获取到计算后的大小
if (status != SingleRequest.Status.WAITING_FOR_SIZE) {
return;
}
status = SingleRequest.Status.RUNNING;
float sizeMultiplier = requestOptions.getSizeMultiplier();
this.width = maybeApplySizeMultiplier(width, sizeMultiplier);
this.height = maybeApplySizeMultiplier(height, sizeMultiplier);
if (IS_VERBOSE_LOGGABLE) {
logV("finished setup for calling load in " + LogTime.getElapsedMillis(startTime));
}
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.getUseUnlimitedSourceGeneratorsPool(),
requestOptions.getUseAnimationPool(),
requestOptions.getOnlyRetrieveFromCache(),
this,
callbackExecutor);
// This is a hack that's only useful for testing right now where loads complete synchronously
// even though under any executor running on any thread but the main thread, the load would
// have completed asynchronously.
if (status != SingleRequest.Status.RUNNING) {
loadStatus = null;
}
if (IS_VERBOSE_LOGGABLE) {
logV("finished onSizeReady in " + LogTime.getElapsedMillis(startTime));
}
}
}主要的代码是engine.load。
/**
* /**
*所有的请求流程都如下：
*1.检查内存缓存并提供缓存的资源
*2.检查当前使用的资源，并返回当前的活跃资源
*3.检查当前的加载进度，并将cb添加到正在进行的加载进度中
*4.开始一个新的加载
*
* @param glideContext
* @param model
* @param signature
* @param width
* @param height
* @param resourceClass
* @param transcodeClass
* @param priority
* @param diskCacheStrategy
* @param transformations
* @param isTransformationRequired
* @param isScaleOnlyOrNoTransform
* @param options
* @param isMemoryCacheable
* @param useUnlimitedSourceExecutorPool
* @param useAnimationPool
* @param onlyRetrieveFromCache
* @param cb
* @param callbackExecutor
* @param <R>
* @return
*/
public <R> Engine.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,
Executor callbackExecutor) {
long startTime = VERBOSE_IS_LOGGABLE ? LogTime.getLogTime() : 0;
//构造一个key
EngineKey key =
keyFactory.buildKey(
model,
signature,
width,
height,
transformations,
resourceClass,
transcodeClass,
options);
EngineResource<?> memoryResource;
synchronized (this) {
//通过这个key去缓存中看是不是存在资源，loadFromMemory里面会先去活跃资源缓存池中获取，
// 没有的话再去内存缓存中获取，活跃资源即现在正在被其他组件使用的资源。
memoryResource = loadFromMemory(key, isMemoryCacheable, startTime);
if (memoryResource == null) {
return waitForExistingOrStartNewJob(
glideContext,
model,
signature,
width,
height,
resourceClass,
transcodeClass,
priority,
diskCacheStrategy,
transformations,
isTransformationRequired,
isScaleOnlyOrNoTransform,
options,
isMemoryCacheable,
useUnlimitedSourceExecutorPool,
useAnimationPool,
onlyRetrieveFromCache,
cb,
callbackExecutor,
key,
startTime);
}
}
// Avoid calling back while holding the engine lock, doing so makes it easier for callers to
// deadlock.
cb.onResourceReady(memoryResource, DataSource.MEMORY_CACHE);
return null;
}如果找得到资源，那么就回调cb.onResourceReady，不然的话会走waitForExistingOrStartNewJob。
我们进去看一下：
private <R> Engine.LoadStatus waitForExistingOrStartNewJob(
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,
Executor callbackExecutor,
EngineKey key,
long startTime) {
//通过key获取EngineJob，EngineJob负责开启线程异步加载。
EngineJob<?> current = jobs.get(key, onlyRetrieveFromCache);
if (current != null) {
current.addCallback(cb, callbackExecutor);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Added to existing load", startTime, key);
}
return new Engine.LoadStatus(cb, current);
}
//没有EngineJob则构建一个
EngineJob<R> engineJob =
engineJobFactory.build(
key,
isMemoryCacheable,
useUnlimitedSourceExecutorPool,
useAnimationPool,
onlyRetrieveFromCache);
//负责给图片解码等一些复杂操作
DecodeJob<R> decodeJob =
decodeJobFactory.build(
glideContext,
model,
key,
signature,
width,
height,
resourceClass,
transcodeClass,
priority,
diskCacheStrategy,
transformations,
isTransformationRequired,
isScaleOnlyOrNoTransform,
onlyRetrieveFromCache,
options,
engineJob);
jobs.put(key, engineJob);
engineJob.addCallback(cb, callbackExecutor);
//运行
engineJob.start(decodeJob);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Started new load", startTime, key);
}
return new Engine.LoadStatus(cb, engineJob);
}
public synchronized void start(DecodeJob<R> decodeJob) {
this.decodeJob = decodeJob;
GlideExecutor executor =
decodeJob.willDecodeFromCache() ? diskCacheExecutor : getActiveSourceExecutor();
executor.execute(decodeJob);
}如果要从磁盘缓存中去解码的话，就获取diskCacheExecutor，否则就用针对原始资源的一个执行器。
在executor.execute(decodeJob)之后便切换到子线程了，我们到DecodeJob里面去看一下。
@Override
public void run() {
// This should be much more fine grained, but since Java's thread pool implementation silently
// swallows all otherwise fatal exceptions, this will at least make it obvious to developers
// that something is failing.
GlideTrace.beginSectionFormat("DecodeJob#run(model=%s)", model);
// Methods in the try statement can invalidate currentFetcher, so set a local variable here to
// ensure that the fetcher is cleaned up either way.
DataFetcher<?> localFetcher = currentFetcher;
try {
if (isCancelled) {
notifyFailed();
return;
}
runWrapped();
} catch (CallbackException e) {
// If a callback not controlled by Glide throws an exception, we should avoid the Glide
// specific debug logic below.
throw e;
} catch (Throwable t) {
// Catch Throwable and not Exception to handle OOMs. Throwables are swallowed by our
// usage of .submit() in GlideExecutor so we're not silently hiding crashes by doing this. We
// are however ensuring that our callbacks are always notified when a load fails. Without this
// notification, uncaught throwables never notify the corresponding callbacks, which can cause
// loads to silently hang forever, a case that's especially bad for users using Futures on
// background threads.
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(
TAG,
"DecodeJob threw unexpectedly" + ", isCancelled: " + isCancelled + ", stage: " + stage,
t);
}
// When we're encoding we've already notified our callback and it isn't safe to do so again.
if (stage != Stage.ENCODE) {
throwables.add(t);
notifyFailed();
}
if (!isCancelled) {
throw t;
}
throw t;
} finally {
// Keeping track of the fetcher here and calling cleanup is excessively paranoid, we call
// close in all cases anyway.
if (localFetcher != null) {
localFetcher.cleanup();
}
GlideTrace.endSection();
}
}主要是runWrapped();
private void runWrapped() {
switch (runReason) {
case INITIALIZE:
stage = getNextStage(Stage.INITIALIZE);
currentGenerator = getNextGenerator();
runGenerators();
break;
case SWITCH_TO_SOURCE_SERVICE:
runGenerators();
break;
case DECODE_DATA:
decodeFromRetrievedData();
break;
default:
throw new IllegalStateException("Unrecognized run reason: " + runReason);
}
}当INITIALIZE或者SWITCH_TO_SOURCE_SERVICE的时候，走runGenerators()。这两种是没有缓存的情况下。
runGenerators()：
private void runGenerators() {
currentThread = Thread.currentThread();
startFetchTime = LogTime.getLogTime();
boolean isStarted = false;
while (!isCancelled
&& currentGenerator != null
&& !(isStarted = currentGenerator.startNext())) {
stage = getNextStage(stage);
currentGenerator = getNextGenerator();
if (stage == Stage.SOURCE) {
reschedule();
return;
}
}
// We've run out of stages and generators, give up.
if ((stage == Stage.FINISHED || isCancelled) && !isStarted) {
notifyFailed();
}
// Otherwise a generator started a new load and we expect to be called back in
// onDataFetcherReady.
}重点：currentGenerator.startNext()。实现startNext方法的有三个：
而我们的currentGenerator是哪一个呢？
回头看runWrapped
case INITIALIZE:
stage = getNextStage(Stage.INITIALIZE);
currentGenerator = getNextGenerator();
runGenerators();点进去getNextGenerator，结合status的值便可以知道返回的是SourceGenerator。（我们讨论的是初次加载没有缓存的情况）
我们来到SourceGenerator的startNext()方法：
@Override
public boolean startNext() {
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()) {
loadData = helper.getLoadData().get(loadDataListIndex++);
if (loadData != null
&& (helper.getDiskCacheStrategy().isDataCacheable(loadData.fetcher.getDataSource())
|| helper.hasLoadPath(loadData.fetcher.getDataClass()))) {
started = true;
startNextLoad(loadData);
}
}
return started;
}如果sourceCacheGenerator 不为null，就调用它的startNext，在里面去获取modelLoader，然后去加载资源，modelLoader即模型加载器，Glide初始化的时候注册了很多模型加载器。
registry
.append(int.class, InputStream.class, resourceLoaderStreamFactory)
.append(int.class, ParcelFileDescriptor.class, resourceLoaderFileDescriptorFactory)
.append(Integer.class, InputStream.class, resourceLoaderStreamFactory)
.append(Integer.class, ParcelFileDescriptor.class, resourceLoaderFileDescriptorFactory)
.append(Integer.class, Uri.class, resourceLoaderUriFactory)
.append(int.class, AssetFileDescriptor.class, resourceLoaderAssetFileDescriptorFactory)
.append(Integer.class, AssetFileDescriptor.class, resourceLoaderAssetFileDescriptorFactory)
.append(int.class, Uri.class, resourceLoaderUriFactory)
.append(String.class, InputStream.class, new DataUrlLoader.StreamFactory<String>())
.append(Uri.class, InputStream.class, new DataUrlLoader.StreamFactory<Uri>())如append(Uri.class, InputStream.class, new DataUrlLoader.StreamFactory<Uri>())
将Uri对象转换为InputStream，模型加载器为DataUrlLoader.StreamFactory，也就是说我们加载的时候如果传进来的是一个uri对象，那么最终会被转换为InputStream。
我们不进去看，直接看接下来的代码。
loadData = helper.getLoadData().get(loadDataListIndex++);
loadData里面包含着：
sourceKey：标识这个加载的原始资源的key
alternateKeys：备用的缓存key指向相同的数据
DataFetcher：用来获取没有在缓存中发现的数据（即需要去加载的，modelLoader中都包含着这个）
接下来看：
startNextLoad(loadData);
private void startNextLoad(final LoadData<?> toStart) {
loadData.fetcher.loadData(
helper.getPriority(),
new DataCallback<Object>() {
@Override
public void onDataReady(@Nullable Object data) {
if (isCurrentRequest(toStart)) {
onDataReadyInternal(toStart, data);
}
}
@Override
public void onLoadFailed(@NonNull Exception e) {
if (isCurrentRequest(toStart)) {
onLoadFailedInternal(toStart, e);
}
}
});
}loadData.fetcher.loadData：这里是我们真正去加载资源的地方。
点击进去loadeData，发现好多实现了该方法的类。那我们这里的Fetcher究竟是哪一个呢？
首先从名字来看，如果我们加载的是网络资源，那么就是：HttpUrlFetcher。
这个HttpUrlFetcher跟我们的modelLoader是什么关系呢
我们可以看出LoadData在ModelLoader类中。
查看HttpUrlFetcher的调用可以追溯到HttpGlideUrlLoader。
@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) {
modelCache.put(model, 0, 0, model);
url = model;
}
}
int timeout = options.get(TIMEOUT);
return new LoadData<>(url, new HttpUrlFetcher(url, timeout));
}我们可以看出HttpGlideUrlLoader实现了ModelLoader的方法，buildLoadData，而在buildLoadData中返回了一个LoadData对象，这个对象传入的就是HttpUrlFetcher。
这个buildLoadData什么时候被调用的呢？
我们回到startNext方法，loadData = helper.getLoadData().get(loadDataListIndex++);的getLoadData()里面：
好，那么我们看HttpUrlFetcher的loadData();
@Override
public void loadData(
@NonNull Priority priority, @NonNull DataCallback<? super InputStream> callback) {
long startTime = LogTime.getLogTime();
try {
InputStream result = loadDataWithRedirects(glideUrl.toURL(), 0, null, glideUrl.getHeaders());
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));
}
}
}loadDataWithRedirects返回了InputStream，然后callback回调。
我们进去loadDataWithRedirects看可以发现这个方法其实是去请求网络，我们就不细看了。
private void startNextLoad(final LoadData<?> toStart) {
loadData.fetcher.loadData(
helper.getPriority(),
new DataCallback<Object>() {
@Override
public void onDataReady(@Nullable Object data) {
if (isCurrentRequest(toStart)) {
onDataReadyInternal(toStart, data);
}
}
@Override
public void onLoadFailed(@NonNull Exception e) {
if (isCurrentRequest(toStart)) {
onLoadFailedInternal(toStart, e);
}
}
});
}回调后调用onDataReadyInternal(toStart, data);
且看一下：
@SuppressWarnings("WeakerAccess")
@Synthetic
void onDataReadyInternal(LoadData<?> loadData, Object data) {
DiskCacheStrategy diskCacheStrategy = helper.getDiskCacheStrategy();
if (data != null && diskCacheStrategy.isDataCacheable(loadData.fetcher.getDataSource())) {
dataToCache = data;
// We might be being called back on someone else's thread. Before doing anything, we should
// reschedule to get back onto Glide's thread.
cb.reschedule();
} else {
cb.onDataFetcherReady(
loadData.sourceKey,
data,
loadData.fetcher,
loadData.fetcher.getDataSource(),
originalKey);
}
}我们看这个方法：onDataFetcherReady
查看一下便可以知道会回调DecodeJob中的方法：
@Override
public void onDataFetcherReady(
Key sourceKey, Object data, DataFetcher<?> fetcher, DataSource dataSource, Key attemptedKey) {
this.currentSourceKey = sourceKey;
this.currentData = data;
this.currentFetcher = fetcher;
this.currentDataSource = dataSource;
this.currentAttemptingKey = attemptedKey;
if (Thread.currentThread() != currentThread) {
runReason = RunReason.DECODE_DATA;
callback.reschedule(this);
} else {
GlideTrace.beginSection("DecodeJob.decodeFromRetrievedData");
try {
decodeFromRetrievedData();
} finally {
GlideTrace.endSection();
}
}
}到此我们就完成了加网络资源的过程，接下来就是解码等等的操作了。
我们看decodeFromRetrievedData：
里面有一句：
resource = decodeFromData(currentFetcher, currentData, currentDataSource);
将资源解码成Resource。
我们追踪进去：
decodeFromData -> decodeFromFetcher -> runLoadPath -> path.load -> loadWithExceptionList
loadWithExceptionList里面便开始进行我们的解码操作了。
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 {
result = path.decode(rewinder, width, height, options, decodeCallback);
} catch (GlideException e) {
exceptions.add(e);
}
if (result != null) {
break;
}
}我们看：
result = path.decode(rewinder, width, height, options, decodeCallback);
public Resource<Transcode> decode(
DataRewinder<DataType> rewinder,
int width,
int height,
@NonNull Options options,
DecodeCallback<ResourceType> callback)
throws GlideException {
Resource<ResourceType> decoded = decodeResource(rewinder, width, height, options);
Resource<ResourceType> transformed = callback.onResourceDecoded(decoded);
return transcoder.transcode(transformed, options);
}我们看decodeResource -> decodeResourceWithList
@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
//遍历获取解码器
for (int i = 0, size = decoders.size(); i < size; i++) {
ResourceDecoder<DataType, ResourceType> decoder = decoders.get(i);
try {
DataType data = rewinder.rewindAndGet();
//该解码器是否可以解码该数据
if (decoder.handles(data, options)) {
//获取数据
data = rewinder.rewindAndGet();
//解码
result = decoder.decode(data, width, height, options);
}
// Some decoders throw unexpectedly. If they do, we shouldn't fail the entire load path, but
// instead log and continue. See #2406 for an example.
} 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;
}获取对应的解码器后用decode方法进行解码。Glide初始化的时候便注册了一大堆解码器，如：
.append(
Registry.BUCKET_GIF,
InputStream.class,
GifDrawable.class,
new StreamGifDecoder(imageHeaderParsers, byteBufferGifDecoder, arrayPool))对于Gif类型，将InputStream解码为GifDrawable，解码器为StreamGifDecoder
接下来我们回到这个方法：
public Resource<Transcode> decode(
DataRewinder<DataType> rewinder,
int width,
int height,
@NonNull Options options,
DecodeCallback<ResourceType> callback)
throws GlideException {
Resource<ResourceType> decoded = decodeResource(rewinder, width, height, options);
Resource<ResourceType> transformed = callback.onResourceDecoded(decoded);
return transcoder.transcode(transformed, options);
}Resource<ResourceType> transformed = callback.onResourceDecoded(decoded);
这个方法里面便是对我们的资源进行了变换。
往下追溯到这个方法：
@Synthetic
@NonNull
<Z> Resource<Z> onResourceDecoded(DataSource dataSource, @NonNull Resource<Z> decoded) {
@SuppressWarnings("unchecked")
Class<Z> resourceSubClass = (Class<Z>) decoded.get().getClass();
Transformation<Z> appliedTransformation = null;
Resource<Z> transformed = decoded;
if (dataSource != DataSource.RESOURCE_DISK_CACHE) {
appliedTransformation = decodeHelper.getTransformation(resourceSubClass);
transformed = appliedTransformation.transform(glideContext, decoded, width, height);
}
// TODO: Make this the responsibility of the Transformation.
if (!decoded.equals(transformed)) {
decoded.recycle();
}
final EncodeStrategy encodeStrategy;
final ResourceEncoder<Z> encoder;
if (decodeHelper.isResourceEncoderAvailable(transformed)) {
encoder = decodeHelper.getResultEncoder(transformed);
encodeStrategy = encoder.getEncodeStrategy(options);
} else {
encoder = null;
encodeStrategy = EncodeStrategy.NONE;
}
Resource<Z> result = transformed;
boolean isFromAlternateCacheKey = !decodeHelper.isSourceKey(currentSourceKey);
if (diskCacheStrategy.isResourceCacheable(
isFromAlternateCacheKey, dataSource, encodeStrategy)) {
if (encoder == null) {
throw new Registry.NoResultEncoderAvailableException(transformed.get().getClass());
}
final Key key;
switch (encodeStrategy) {
case SOURCE:
key = new DataCacheKey(currentSourceKey, signature);
break;
case TRANSFORMED:
key =
new ResourceCacheKey(
decodeHelper.getArrayPool(),
currentSourceKey,
signature,
width,
height,
appliedTransformation,
resourceSubClass,
options);
break;
default:
throw new IllegalArgumentException("Unknown strategy: " + encodeStrategy);
}
LockedResource<Z> lockedResult = LockedResource.obtain(transformed);
deferredEncodeManager.init(key, encoder, lockedResult);
result = lockedResult;
}
return result;
}首先获取Transformation，然后调用transform方法进行变换处理。
返回resource之后回到decodeFromRetrievedData方法。
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 {
resource = decodeFromData(currentFetcher, currentData, currentDataSource);
} catch (GlideException e) {
e.setLoggingDetails(currentAttemptingKey, currentDataSource);
throwables.add(e);
}
if (resource != null) {
notifyEncodeAndRelease(resource, currentDataSource);
} else {
runGenerators();
}
}我们沿着方法进入notifyEncodeAndRelease ---> notifyComplete ----> onResourceReady ------>notifyCallbacksOfResult
。。。。算了写的到这里好累，接下来不写了自己看，就是去设置资源。
https://www.cnblogs.com/tangZH/p/12543154.html
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