由于into过程篇幅过长，不利于阅读，因此把Engine#load过程单独拆出来分析。
1.RequestBuilder#into
/**
* Sets the {@link ImageView} the resource will be loaded into, cancels any existing loads into
* the view, and frees any resources Glide may have previously loaded into the view so they may be
* reused.
*
* @see RequestManager#clear(Target)
* @param view The view to cancel previous loads for and load the new resource into.
* @return The {@link com.bumptech.glide.request.target.Target} used to wrap the given {@link
* ImageView}.
*/
@NonNull
public ViewTarget<ImageView, TranscodeType> into(@NonNull ImageView view) {
//非主线程调用抛异常
Util.assertMainThread();
//Imageviw不能为null
Preconditions.checkNotNull(view);
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.
//根据ScaleType克隆不同的RequestOptions对象，为的是去除上一次参数的影响。
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.
}
}
//glideContext.buildImageViewTarget(view, transcodeClass)得到的结果是DrawableImageViewTarget对象
return into(
glideContext.buildImageViewTarget(view, transcodeClass),
/*targetListener=*/ null,
requestOptions,
Executors.mainThreadExecutor());
}
private <Y extends Target<TranscodeType>> Y into(
@NonNull Y target,
@Nullable RequestListener<TranscodeType> targetListener,
BaseRequestOptions<?> options,
Executor callbackExecutor) {
//Imageview为空抛出异常
Preconditions.checkNotNull(target);
//未设置model参数抛出异常
if (!isModelSet) {
throw new IllegalArgumentException("You must call #load() before calling #into()");
}
//构建Request请求
Request request = buildRequest(target, targetListener, options, callbackExecutor);
//获取ViewTarget缓存的请求
Request previous = target.getRequest();
//如果Imageview中缓存的上一个request对象新创建的request内容相同，且未设置不使用内存缓存且previous请求未完成，则复用previous请求。
if (request.isEquivalentTo(previous)
&& !isSkipMemoryCacheWithCompletePreviousRequest(options, previous)) {
//释放新创建的请求。
request.recycle();
//如果previous请求是完成状态，则重新发送请求。这样做的目的是优化了比如占位符等相关的设置，复用了之前请求里对view的设置
if (!Preconditions.checkNotNull(previous).isRunning()) {
previous.begin();
}
return target;
}
//清楚View中缓存的request对象
requestManager.clear(target);
//在View#settag方法中缓存request对象
target.setRequest(request);
//发送请求
requestManager.track(target, request);
return target;
}2.RequestManager#track
synchronized void track(@NonNull Target<?> target, @NonNull Request request) {
//添加到TargetTracker，用于执行生命周期回调
targetTracker.track(target);
//开始请求
requestTracker.runRequest(request);
}
3.RequestTracker#runRequest
public void runRequest(@NonNull Request request) {
//缓存request请求
requests.add(request);
if (!isPaused) {
//执行请求
request.begin();
} else {
request.clear();
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Paused, delaying request");
}
//暂停状态不发送请求，添加到PendingRequest对象，调用resumeRequests方法会重新执行请求。
//pendingRequests队列是为了强引用暂停状态下提交的request请求防止被gc。
pendingRequests.add(request);
}
}Request是一个接口，那么他的实现类是什么呢，我们回到第一步的buildRequest(target, targetListener, options, callbackExecutor)方法。
4. RequestBuilder#buildRequest
private Request buildRequest(
Target<TranscodeType> target,
@Nullable RequestListener<TranscodeType> targetListener,
BaseRequestOptions<?> requestOptions,
Executor callbackExecutor) {
//transitionOptions是图片渲染时的过度效果，不设置时，会先去取transcodeClass父类的，取不到使用默认的
return buildRequestRecursive(
target,
targetListener,
/*parentCoordinator=*/ null,
transitionOptions,
requestOptions.getPriority(),
requestOptions.getOverrideWidth(),
requestOptions.getOverrideHeight(),
requestOptions,
//回调线程池，在主线程执行
callbackExecutor);
}5.RequestBuilder#buildRequestRecursive
private Request buildRequestRecursive(
Target<TranscodeType> target,
@Nullable RequestListener<TranscodeType> targetListener,
@Nullable RequestCoordinator parentCoordinator,
TransitionOptions<?, ? super TranscodeType> transitionOptions,
Priority priority,
int overrideWidth,
int overrideHeight,
BaseRequestOptions<?> requestOptions,
Executor callbackExecutor) {
// Build the ErrorRequestCoordinator first if necessary so we can update parentCoordinator.
ErrorRequestCoordinator errorRequestCoordinator = null;
//如果设置了errorBuilder，构建errorRequestCoordinator对象
if (errorBuilder != null) {
errorRequestCoordinator = new ErrorRequestCoordinator(parentCoordinator);
parentCoordinator = errorRequestCoordinator;
}
//构建缩略图请求
Request mainRequest =
buildThumbnailRequestRecursive(
target,
targetListener,
parentCoordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight,
requestOptions,
callbackExecutor);
//未设置error请求，返回mainRequest
if (errorRequestCoordinator == null) {
return mainRequest;
}
int errorOverrideWidth = errorBuilder.getOverrideWidth();
int errorOverrideHeight = errorBuilder.getOverrideHeight();
if (Util.isValidDimensions(overrideWidth, overrideHeight) && !errorBuilder.isValidOverride()) {
errorOverrideWidth = requestOptions.getOverrideWidth();
errorOverrideHeight = requestOptions.getOverrideHeight();
}
Request errorRequest =
errorBuilder.buildRequestRecursive(
target,
targetListener,
errorRequestCoordinator,
errorBuilder.transitionOptions,
errorBuilder.getPriority(),
errorOverrideWidth,
errorOverrideHeight,
errorBuilder,
callbackExecutor);
errorRequestCoordinator.setRequests(mainRequest, errorRequest);
return errorRequestCoordinator;
}无论是errorBuilder还是还是正常的builder都会调用到buildThumbnailRequestRecursive方法。
6. RequestBuilder#buildThumbnailRequestRecursive
private Request buildThumbnailRequestRecursive(
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) {
//设置了缩略图的RequestBuilder
// 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();
}
//管理全尺寸和缩略图两个请求
ThumbnailRequestCoordinator coordinator = new ThumbnailRequestCoordinator(parentCoordinator);
//全尺寸图片请求
Request fullRequest =
obtainRequest(
target,
targetListener,
requestOptions,
coordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight,
callbackExecutor);
isThumbnailBuilt = true;
//缩略图请求
Request thumbRequest =
thumbnailBuilder.buildRequestRecursive(
target,
targetListener,
coordinator,
thumbTransitionOptions,
thumbPriority,
thumbOverrideWidth,
thumbOverrideHeight,
thumbnailBuilder,
callbackExecutor);
isThumbnailBuilt = false;
coordinator.setRequests(fullRequest, thumbRequest);
return coordinator;
} else if (thumbSizeMultiplier != null) {
//设置缩略图百分比参数thumbSizeMultiplier，则会创建缩略图请求
ThumbnailRequestCoordinator coordinator = new ThumbnailRequestCoordinator(parentCoordinator);
Request fullRequest =
obtainRequest(
target,
targetListener,
requestOptions,
coordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight,
callbackExecutor);
BaseRequestOptions<?> thumbnailOptions =
requestOptions.clone().sizeMultiplier(thumbSizeMultiplier);
Request thumbnailRequest =
obtainRequest(
target,
targetListener,
thumbnailOptions,
coordinator,
transitionOptions,
getThumbnailPriority(priority),
overrideWidth,
overrideHeight,
callbackExecutor);
coordinator.setRequests(fullRequest, thumbnailRequest);
return coordinator;
} else {
// 没有缩略图请求，直接构建全尺寸图片请求
return obtainRequest(
target,
targetListener,
requestOptions,
parentCoordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight,
callbackExecutor);
}
}无论是缩略图请求还是全尺寸请求又或是error请求，他们都是调用的obtainRequest方法创建的请求。
7.RequestBuilder#obtainRequest
private Request obtainRequest(
Target<TranscodeType> target,
RequestListener<TranscodeType> targetListener,
BaseRequestOptions<?> requestOptions,
RequestCoordinator requestCoordinator,
TransitionOptions<?, ? super TranscodeType> transitionOptions,
Priority priority,
int overrideWidth,
int overrideHeight,
Executor callbackExecutor) {
return SingleRequest.obtain(
context,
glideContext,
model,
transcodeClass,
requestOptions,
overrideWidth,
overrideHeight,
priority,
target,
targetListener,
requestListeners,
requestCoordinator,
glideContext.getEngine(),
transitionOptions.getTransitionFactory(),
callbackExecutor);
}Request有多个实现类，我们使用的是SingleRquest方法。所以我们的begin方法就是调用的SingleRequest#begin方法
8. SingleRequest#begin
@Override
public synchronized void begin() {
assertNotCallingCallbacks();
//检查request是否被回收
stateVerifier.throwIfRecycled();
startTime = LogTime.getLogTime();
//model对象为null，加载失败
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;
}
//运行状态不能调用start
if (status == Status.RUNNING) {
throw new IllegalArgumentException("Cannot restart a running request");
}
//如果是完成状态直接回调
if (status == Status.COMPLETE) {
onResourceReady(resource, DataSource.MEMORY_CACHE);
return;
}
//非COMPLETE、RUNNING状态设置为WAITING_FOR_SIZE状态，作为新请求使用
status = Status.WAITING_FOR_SIZE;
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
//设置过overrideWidth和overrideHeight直接调用onSizeReady
onSizeReady(overrideWidth, overrideHeight);
} else {
//计算overrideWidth和overrideHeight大小，计算完成回调onSizeReady
target.getSize(this);
}
//回调onLoadStarted方法
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));
}
}9. SingleRequest#onSizeReady
/** A callback method that should never be invoked directly. */
@Override
public synchronized void onSizeReady(int width, int height) {
stateVerifier.throwIfRecycled();
if (IS_VERBOSE_LOGGABLE) {
logV("Got onSizeReady in " + LogTime.getElapsedMillis(startTime));
}
if (status != Status.WAITING_FOR_SIZE) {
return;
}
//修改为RUNNING状态
status = 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(),
//ResourceCallback对象，资源加载成功会回调
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 != Status.RUNNING) {
loadStatus = null;
}
if (IS_VERBOSE_LOGGABLE) {
logV("finished onSizeReady in " + LogTime.getElapsedMillis(startTime));
}
}
Engine#load方法加载成功后会回调SingleRequest#onResourceReady方法，SingleRequest实现了ResourceCallback接口
10. SingleRequest#onResourceReady
@Override
public synchronized void onResourceReady(Resource<?> resource, DataSource dataSource) {
stateVerifier.throwIfRecycled();
loadStatus = null;
//如果resource为空，则回调加载失败，并抛出异常
if (resource == null) {
GlideException exception =
new GlideException(
"Expected to receive a Resource<R> with an "
+ "object of "
+ transcodeClass
+ " inside, but instead got null.");
onLoadFailed(exception);
return;
}
Object received = resource.get();
if (received == null || !transcodeClass.isAssignableFrom(received.getClass())) {
releaseResource(resource);
GlideException exception =
new GlideException(
"Expected to receive an object of "
+ transcodeClass
+ " but instead"
+ " got "
+ (received != null ? received.getClass() : "")
+ "{"
+ received
+ "} inside"
+ " "
+ "Resource{"
+ resource
+ "}."
+ (received != null
? ""
: " "
+ "To indicate failure return a null Resource "
+ "object, rather than a Resource object containing null data."));
onLoadFailed(exception);
return;
}
if (!canSetResource()) {
releaseResource(resource);
// We can't put the status to complete before asking canSetResource().
status = Status.COMPLETE;
return;
}
onResourceReady((Resource<R>) resource, (R) received, dataSource);
}
/**
* Internal {@link #onResourceReady(Resource, DataSource)} where arguments are known to be safe.
*
* @param resource original {@link Resource}, never <code>null</code>
* @param result object returned by {@link Resource#get()}, checked for type and never <code>null
* </code>
*/
private synchronized void onResourceReady(Resource<R> resource, R result, DataSource dataSource) {
// We must call isFirstReadyResource before setting status.
boolean isFirstResource = isFirstReadyResource();
status = Status.COMPLETE;
this.resource = resource;
if (glideContext.getLogLevel() <= Log.DEBUG) {
Log.d(
GLIDE_TAG,
"Finished loading "
+ result.getClass().getSimpleName()
+ " from "
+ dataSource
+ " for "
+ model
+ " with size ["
+ width
+ "x"
+ height
+ "] in "
+ LogTime.getElapsedMillis(startTime)
+ " ms");
}
isCallingCallbacks = true;
try {
//这个状态就是为了判断，回调方法onResourceReady是否返回true，
//如为true，则不执行图片渲染到指定View。即target.onResourceReady(result, animation)方法
boolean anyListenerHandledUpdatingTarget = false;
if (requestListeners != null) {
for (RequestListener<R> listener : requestListeners) {
anyListenerHandledUpdatingTarget |=
listener.onResourceReady(result, model, target, dataSource, isFirstResource);
}
}
anyListenerHandledUpdatingTarget |=
targetListener != null
&& targetListener.onResourceReady(result, model, target, dataSource, isFirstResource);
if (!anyListenerHandledUpdatingTarget) {
Transition<? super R> animation = animationFactory.build(dataSource, isFirstResource);
//这个地方调用的是ImageViewTarget#onResourceReady方法。
target.onResourceReady(result, animation);
}
} finally {
isCallingCallbacks = false;
}
notifyLoadSuccess();
}在前面文章with过程中，我们讲到target是DrawableImageViewTarget对象，DrawableImageViewTarget父类为ImageViewTarget，因此这个地方调用的是ImageViewTarget#onResourceReady方法。
11. ImageViewTarget#onResourceReady
@Override
public void onResourceReady(@NonNull Z resource, @Nullable Transition<? super Z> transition) {
if (transition == null || !transition.transition(resource, this)) {
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.
setResource(resource);
maybeUpdateAnimatable(resource);
}
private void maybeUpdateAnimatable(@Nullable Z resource) {
if (resource instanceof Animatable) {
animatable = (Animatable) resource;
animatable.start();
} else {
animatable = null;
}
}setResource方法调用了view.setImageDrawable(resource)这样图片就显示到了ImageView。
接下来我们会分析Engine#load过程，这是Glide的核心部分。