前言
上一篇探究Glide的运行原理(1)
)我们主要了解了一下Glide的简介以及简单的使用，同时也对Glide.with().load()方法进行了相关分析；
接下来我们则继续分析到
Gilde.with().load(url).into(view) ：
首先我们进入到RequestBuilder的into方法
@NonNull
public ViewTarget<ImageView, TranscodeType> into(@NonNull ImageView view) {
Util.assertMainThread(); // 判断主线程
Preconditions.checkNotNull(view); // 判断view部位空
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()) { // 根据定义scaleType裁剪
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(
glideContext.buildImageViewTarget(view, transcodeClass),
/*targetListener=*/ null,
requestOptions,
Executors.mainThreadExecutor());
先会对View定义的scaleType进行裁剪，看下CENTER_CROP裁剪实现；requestOptions = requestOptions.clone().optionalCenterCrop() ，这里的requestOptions 为BaseRequestOptions类的实列，同时BaseRequestOptions为RequsetBuilder的子类 ，查看BaseRequestOptions的optionalCenterCrop方法：
@NonNull
@CheckResult
public T optionalCenterCrop() {
return optionalTransform(DownsampleStrategy.CENTER_OUTSIDE, new CenterCrop());
}
@NonNull
final T optionalTransform(
@NonNull DownsampleStrategy downsampleStrategy,
@NonNull Transformation<Bitmap> transformation) {
if (isAutoCloneEnabled) {
return clone().optionalTransform(downsampleStrategy, transformation);
}
downsample(downsampleStrategy);
// 转换信息
return transform(transformation, /*isRequired=*/ false);
}
@NonNull
@CheckResult
public T downsample(@NonNull DownsampleStrategy strategy) {
// 设置相关转换图片配置
return set(DownsampleStrategy.OPTION, Preconditions.checkNotNull(strategy));
}
/**
*配置转换的信息
*/
@NonNull
T transform(@NonNull Transformation<Bitmap> transformation, boolean isRequired) {
if (isAutoCloneEnabled) {
return clone().transform(transformation, isRequired);
}
DrawableTransformation drawableTransformation =
new DrawableTransformation(transformation, isRequired);
transform(Bitmap.class, transformation, isRequired);
transform(Drawable.class, drawableTransformation, isRequired);
// TODO: remove BitmapDrawable decoder and this transformation.
// Registering as BitmapDrawable is simply an optimization to avoid some iteration and
// isAssignableFrom checks when obtaining the transformation later on. It can be removed without
// affecting the functionality.
transform(BitmapDrawable.class, drawableTransformation.asBitmapDrawable(), isRequired);
transform(GifDrawable.class, new GifDrawableTransformation(transformation), isRequired);
return selfOrThrowIfLocked();
}
@NonNull
<Y> T transform(
@NonNull Class<Y> resourceClass,
@NonNull Transformation<Y> transformation,
boolean isRequired) {
if (isAutoCloneEnabled) {
return clone().transform(resourceClass, transformation, isRequired);
}
Preconditions.checkNotNull(resourceClass);
Preconditions.checkNotNull(transformation);
transformations.put(resourceClass, transformation);
fields |= TRANSFORMATION;
isTransformationAllowed = true;
fields |= TRANSFORMATION_ALLOWED;
// Always set to false here. Known scale only transformations will call this method and then
// set isScaleOnlyOrNoTransform to true immediately after.
isScaleOnlyOrNoTransform = false;
if (isRequired) {
fields |= TRANSFORMATION_REQUIRED;
isTransformationRequired = true;
}
return selfOrThrowIfLocked();
}
可以看到这里主要是配置图片的各种转换信息；
继续往下查看前，我们先看先看下RequestBuilder的into()方法的返回ViewTarget的类结构:
public abstract class ViewTarget<T extends View, Z> extends BaseTarget<Z> {
}
@Deprecated
public abstract class BaseTarget<Z> implements Target<Z> {
private Request request;
@Override
public void setRequest(@Nullable Request request) {
this.request = request;
}
@Override
@Nullable
public Request getRequest() {
return request;
}
@Override
public void onLoadCleared(@Nullable Drawable placeholder) {
// Do nothing.
}
@Override
public void onLoadStarted(@Nullable Drawable placeholder) {
// Do nothing.
}
@Override
public void onLoadFailed(@Nullable Drawable errorDrawable) {
// Do nothing.
}
@Override
public void onStart() {
// Do nothing.
}
@Override
public void onStop() {
// Do nothing.
}
@Override
public void onDestroy() {
// Do nothing.
}
}
public interface Target<R> extends LifecycleListener {
/** Indicates that we want the resource in its original unmodified width and/or height. */
int SIZE_ORIGINAL = Integer.MIN_VALUE;
void onLoadStarted(@Nullable Drawable placeholder);
void onLoadStarted(android.graphics.drawable.Drawable) }
void onLoadFailed(@Nullable Drawable errorDrawable);
void onResourceReady(@NonNull R resource, @Nullable Transition<? super R> transition);
void onLoadCleared(@Nullable Drawable placeholder);
void getSize(@NonNull SizeReadyCallback cb);
void removeCallback(@NonNull SizeReadyCallback cb);
void setRequest(@Nullable Request request);
@Nullable
Request getRequest();
}
public interface LifecycleListener {
void onStart();
void onStop();
void onDestroy();
}
ViewTarget继承了BaseTarget类，BaseTarget实现了Target类，而Target类基础LifecycleListener；
这样和生命周期进行了关联。之前我们讲到Glide为了生命周期管理的时候，在Fragment类中也定义过这样一个LifecycleListener，类似的情况，同样对生命周期进行管理。
此时继续查看RequestBuilder的into方法中的最后的执行方法，
into(
glideContext.buildImageViewTarget(view, transcodeClass),
/targetListener=/ null,
requestOptions,
Executors.mainThreadExecutor());
先看该方法第一个传入参数glideContext.buildImageViewTarget(view, transcodeClass)；这里传参view为ImageView，而transcodeClass在Glide.load(url)的时候，如果传的url为String类型，此处的transcodeClass传入的是Draw.class,进入GlideContext类中的buildImageViewTarget方法里面继续查看：
@NonNull
public <X> ViewTarget<ImageView, X> buildImageViewTarget(
@NonNull ImageView imageView, @NonNull Class<X> transcodeClass) {
return imageViewTargetFactory.buildTarget(imageView, transcodeClass);
}
public class ImageViewTargetFactory {
@NonNull
@SuppressWarnings("unchecked")
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)");
}
}
}
这里可以看到，build会根据传入Glide的load方法传入不同类型，这里会根据工厂创建不同的Target；此时匹配到Drawable则应该返回(ViewTarget<ImageView, Z>) new DrawableImageViewTarget(view)；这里的DrawableImageViewTarget继承子ImageViewTarger；而ImageViewTarger则继承自ViewTarget；
继续查看ReqestBuilder的into()中调用的into方法：
private <Y extends Target<TranscodeType>> Y into(
@NonNull Y target,
@Nullable RequestListener<TranscodeType> targetListener,
BaseRequestOptions<?> options,
Executor callbackExecutor) {
Preconditions.checkNotNull(target);
if (!isModelSet) {
throw new IllegalArgumentException("You must call #load() before calling #into()");
}
//创建Request
Request request = buildRequest(target, targetListener, options, callbackExecutor);
// 取出target原有的Request
Request previous = target.getRequest();
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);
target.setRequest(request);// request设置给target
requestManager.track(target, request);// 执行
return target;
}
上面的代码主要创建的Request，然后会通过target中之前设置的Request和新建的对比，如果一样则直接中begin方法；否则把request设置给target后，通过requestManager进行执行；
我们先看下创建方法 Request request = buildRequest(target, targetListener, options, callbackExecutor)，进入RequestBuilder的buildRequest方法：
//创建Request
private Request buildRequest(
Target<TranscodeType> target,
@Nullable RequestListener<TranscodeType> targetListener,
BaseRequestOptions<?> requestOptions,
Executor callbackExecutor) {
return buildRequestRecursive(
/*requestLock=*/ new Object(),
target,
targetListener,
/*parentCoordinator=*/ null,
transitionOptions,
requestOptions.getPriority(),
requestOptions.getOverrideWidth(),
requestOptions.getOverrideHeight(),
requestOptions,
callbackExecutor);
}
private Request buildRequestRecursive(
Object requestLock,
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;
if (errorBuilder != null) {
errorRequestCoordinator = new ErrorRequestCoordinator(requestLock, parentCoordinator);
parentCoordinator = errorRequestCoordinator;
}
// 创建缩略图的Request
Request mainRequest =
buildThumbnailRequestRecursive(
requestLock,
target,
targetListener,
parentCoordinator,
transitionOptions,
priority,
overrideWidth,
overrideHeight,
requestOptions,
callbackExecutor);
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(
requestLock,
target,
targetListener,
errorRequestCoordinator,
errorBuilder.transitionOptions,
errorBuilder.getPriority(),
errorOverrideWidth,
errorOverrideHeight,
errorBuilder,
callbackExecutor);
errorRequestCoordinator.setRequests(mainRequest, errorRequest);
return errorRequestCoordinator;
}
这里可以看到有个errorRequestCoordinator 应该是错误的Request的构造，mainRequest应该是主要的Request请求，这里的mainRequest主要建造缩略图的一些构造信息。可以进去看看：
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);
}
}
这个方法还真有点长，看的真有点头疼，主要看到最后一个obtainRequest方法;
private Request obtainRequest(
Object requestLock,
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,
requestLock,
model,
transcodeClass,
requestOptions,
overrideWidth,
overrideHeight,
priority,
target,
targetListener,
requestListeners,
requestCoordinator,
glideContext.getEngine(),
transitionOptions.getTransitionFactory(),
callbackExecutor);
}
}
这里通过SingleRequest创建了一个Request实例，进入SingleRequest类的obtain方法：
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) {
return new SingleRequest<>(
context,
glideContext,
requestLock,
model,
transcodeClass,
requestOptions,
overrideWidth,
overrideHeight,
priority,
target,
targetListener,
requestListeners,
requestCoordinator,
engine,
animationFactory,
callbackExecutor);
}
这里创建了SingleRequest实例，SingleRequest同时是Request的子类：
/**
* A {@link Request} that loads a {@link com.bumptech.glide.load.engine.Resource} into a given
* {@link Target}.
*
* @param <R> The type of the resource that will be transcoded from the loaded resource.
*/
public final class SingleRequest<R> implements Request, SizeReadyCallback, ResourceCallback {
A {@link Request} that loads a {@link com.bumptech.glide.load.engine.Resource} into a given
从注释可以看出SingleRequest是为了加载Resource的；
RequestBuilder的buildRequest方法创建了Request类，继续回到上面RequestBuilder流程继续看，Target会对Request进行绑定，进入到Target的实现类ViewTarget里面：
@Override
@Nullable
public Request getRequest() {
Object tag = getTag();
Request request = null;
if (tag != null) {
if (tag instanceof Request) {
request = (Request) tag;
} else {
throw new IllegalArgumentException(
"You must not call setTag() on a view Glide is targeting");
}
}
return request;
}
@Override
public void setRequest(@Nullable Request request) {
setTag(request);
}
private void setTag(@Nullable Object tag) {
isTagUsedAtLeastOnce = true;
view.setTag(tagId, tag);
}
可以看到ViewTarget主要通过Tag和Request进行绑定，可以避免复用导致图片错位问题。
接下来，回到into方法的最后一行requestManager.track(target, request);
进入到RequestManager的track方法：
synchronized void track(@NonNull Target<?> target, @NonNull Request request) {
targetTracker.track(target);
requestTracker.runRequest(request);
}
主要查看requestTracker.runRequest(request)方法，查看RequestTracker类的runRequest方法：
/** 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);
}
}
request.begin()这里的Request实现类为SingleRequest继续去，进入SingleRequest的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");
}
// 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));
}
}
}
// 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;
上述表示一个请求刚开始状态，我们主要先从这里看，这边会通过判断overrideWidth和overrideHeight是否合理调用不同的方法，这边先进入target.getSize(this)（因为我们会发现最终还是会调到onSizeReady方法），查看ViewTarget类：
@CallSuper
@Override
public void getSize(@NonNull SizeReadyCallback cb) {
sizeDeterminer.getSize(cb);
}
进入SizeDeterminer类：
void getSize(@NonNull SizeReadyCallback cb) {
int currentWidth = getTargetWidth();
int currentHeight = getTargetHeight();
if (isViewStateAndSizeValid(currentWidth, currentHeight)) {
cb.onSizeReady(currentWidth, currentHeight);
return;
}
// We want to notify callbacks in the order they were added and we only expect one or two
// callbacks to be added a time, so a List is a reasonable choice.
if (!cbs.contains(cb)) {
cbs.add(cb);
}
if (layoutListener == null) {
ViewTreeObserver observer = view.getViewTreeObserver();
layoutListener = new SizeDeterminerLayoutListener(this);
observer.addOnPreDrawListener(layoutListener);
}
}
可以看到这里最终还是会调用到onSizeReady方法，这个方法其实是SizeReadyCallback类定义的接口方法，而SingleRequest则实现了这个接口；那我们就继续看SingleRequest的onSizeReady方法吧：
@Override
public void onSizeReady(int width, int height) {
stateVerifier.throwIfRecycled();
synchronized (requestLock) {
if (IS_VERBOSE_LOGGABLE) {
logV("Got onSizeReady in " + LogTime.getElapsedMillis(startTime));
}
if (status != Status.WAITING_FOR_SIZE) {
return;
}
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(),
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));
}
}
}
这里大概可以菜刀engine.load(）就应该是加载图片的核心方法了，
我们进入Engin类的load方法中去查看：
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,
Executor callbackExecutor) {
long startTime = VERBOSE_IS_LOGGABLE ? LogTime.getLogTime() : 0;
// 生成一个唯一的key
EngineKey key =
keyFactory.buildKey(
model,
signature,
width,
height,
transformations,
resourceClass,
transcodeClass,
options);
// 内存的资源
EngineResource<?> memoryResource;
synchronized (this) {// 从内存中加载
memoryResource = loadFromMemory(key, isMemoryCacheable, startTime);
// 如果内存中没有
if (memoryResource == null) {// 重新开一个任务去加载资源
return waitForExistingOrStartNewJob(
glideContext,
model,
signature,
width,
height,
resourceClass,
transcodeClass,
priority,
diskCacheStrategy,
transformations,
isTransformationRequired,
isScaleOnlyOrNoTransform,
options,
isMemoryCacheable,
useUnlimitedSourceExecutorPool,
useAnimationPool,
onlyRetrieveFromCache,
cb,
callbackExecutor,
key,
startTime);
}
}
上述的代码我们可以看到egine会根据请求的相关信息先生成一个唯一的key，这个key对应每个请求是唯一的。然后会根据key通过loadFromMemory方法从内存中去查找，没有找到会继续执行waitForExistingOrStartNewJob方法；我们先看下Egine类中的loadFromMemory方法：
@Nullable
private EngineResource<?> loadFromMemory(
EngineKey key, boolean isMemoryCacheable, long startTime) {
if (!isMemoryCacheable) {
return null;
}
EngineResource<?> active = loadFromActiveResources(key);
if (active != null) {
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Loaded resource from active resources", startTime, key);
}
return active;
}
EngineResource<?> cached = loadFromCache(key);
if (cached != null) {
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Loaded resource from cache", startTime, key);
}
return cached;
}
return null;
}
可以看到主要通过loadFromActiveResources和loadFromCache方法从内存中去加载；一个个去看，先看loadFromActiveResources方法：
@Nullable
private EngineResource<?> loadFromActiveResources(Key key) {
EngineResource<?> active = activeResources.get(key);
if (active != null) {
active.acquire();
}
return active;
}
这里就需要看下activeResources的类是怎么存储的了，
final class ActiveResources {
private final boolean isActiveResourceRetentionAllowed;
private final Executor monitorClearedResourcesExecutor;
@VisibleForTesting final Map<Key, ResourceWeakReference> activeEngineResources = new HashMap<>();
private final ReferenceQueue<EngineResource<?>> resourceReferenceQueue = new ReferenceQueue<>();
private ResourceListener listener;
private volatile boolean isShutdown;
@Nullable private volatile DequeuedResourceCallback cb;
ActiveResources(boolean isActiveResourceRetentionAllowed) {
this(
isActiveResourceRetentionAllowed,
java.util.concurrent.Executors.newSingleThreadExecutor(
new ThreadFactory() {
@Override
public Thread newThread(@NonNull final Runnable r) {
return new Thread(
new Runnable() {
@Override
public void run() {
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
r.run();
}
},
"glide-active-resources");
}
}));
}
synchronized void activate(Key key, EngineResource<?> resource) {
ResourceWeakReference toPut =
new ResourceWeakReference(
key, resource, resourceReferenceQueue, isActiveResourceRetentionAllowed);
ResourceWeakReference removed = activeEngineResources.put(key, toPut);
if (removed != null) {
removed.reset();
}
}
@VisibleForTesting
static final class ResourceWeakReference extends WeakReference<EngineResource<?>> {
@SuppressWarnings("WeakerAccess")
@Synthetic
final Key key;
@SuppressWarnings("WeakerAccess")
@Synthetic
final boolean isCacheable;
@Nullable
@SuppressWarnings("WeakerAccess")
@Synthetic
Resource<?> resource;
@Synthetic
@SuppressWarnings("WeakerAccess")
ResourceWeakReference(
@NonNull Key key,
@NonNull EngineResource<?> referent,
@NonNull ReferenceQueue<? super EngineResource<?>> queue,
boolean isActiveResourceRetentionAllowed) {
super(referent, queue);
this.key = Preconditions.checkNotNull(key);
this.resource =
referent.isMemoryCacheable() && isActiveResourceRetentionAllowed
? Preconditions.checkNotNull(referent.getResource())
: null;
isCacheable = referent.isMemoryCacheable();
}
void reset() {
resource = null;
clear();
}
}
可以看到这里存储用的是弱引用WeakReference的hashMap，把资源用弱引用起来。只要垃圾回收机制回收，就会对应把存储资源进行删除。如果这里是空的，则会继续从loadFromCache取内存；
接下里继续看loadFromCache的方法：
private EngineResource<?> loadFromCache(Key key) {
EngineResource<?> cached = getEngineResourceFromCache(key);
if (cached != null) {
cached.acquire();
activeResources.activate(key, cached);
}
return cached;
}
private final MemoryCache cache;
private EngineResource<?> getEngineResourceFromCache(Key key) {
Resource<?> cached = cache.remove(key);
final EngineResource<?> result;
if (cached == null) {
result = null;
} else if (cached instanceof EngineResource) {
// Save an object allocation if we've cached an EngineResource (the typical case).
result = (EngineResource<?>) cached;
} else {
result =
new EngineResource<>(
cached, /*isMemoryCacheable=*/ true, /*isRecyclable=*/ true, key, /*listener=*/ this);
}
return result;
}
这里可以看到getEngineResourceFromCache方法中，主要通过cache进行缓存数据，cache是MemoryCache 的实例类，这里MemoryCache的实现类是LruResourceCache。采用的LRU缓存策略。
/** An LRU in memory cache for {@link com.bumptech.glide.load.engine.Resource}s. */
public class LruResourceCache extends LruCache<Key, Resource<?>> implements MemoryCache {
private ResourceRemovedListener listener;
/**
* Constructor for LruResourceCache.
*
* @param size The maximum size in bytes the in memory cache can use.
*/
public LruResourceCache(long size) {
super(size);
}
@Override
public void setResourceRemovedListener(@NonNull ResourceRemovedListener listener) {
this.listener = listener;
}
@Override
protected void onItemEvicted(@NonNull Key key, @Nullable Resource<?> item) {
if (listener != null && item != null) {
listener.onResourceRemoved(item);
}
}
@Override
protected int getSize(@Nullable Resource<?> item) {
if (item == null) {
return super.getSize(null);
} else {
return item.getSize();
}
}
@SuppressLint("InlinedApi")
@Override
public void trimMemory(int level) {
if (level >= android.content.ComponentCallbacks2.TRIM_MEMORY_BACKGROUND) {
// Entering list of cached background apps
// Evict our entire bitmap cache
clearMemory();
} else if (level >= android.content.ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN
|| level == android.content.ComponentCallbacks2.TRIM_MEMORY_RUNNING_CRITICAL) {
// The app's UI is no longer visible, or app is in the foreground but system is running
// critically low on memory
// Evict oldest half of our bitmap cache
trimToSize(getMaxSize() / 2);
}
}
}
这样的话，Glide就会从LruCache取资源文件，如果取到了继续存到之前的WeakReference中，不然则会返回实例化的EngineResource类；
如果上述两者获取到的资源仍然为空，Egine类程序会继续执行waitForExistingOrStartNewJob方法：
private <R> 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) {
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 LoadStatus(cb, current);
}
EngineJob<R> engineJob =
engineJobFactory.build(
key,
isMemoryCacheable,
useUnlimitedSourceExecutorPool,
useAnimationPool,
onlyRetrieveFromCache);
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);
engineJob.start(decodeJob);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Started new load", startTime, key);
}
return new LoadStatus(cb, engineJob);
}
可以看到，这里主要创建了egineJob 和 decodeJob两个实例化的类。
class EngineJob<R> implements DecodeJob.Callback<R>, Poolable {
private static final EngineResourceFactory DEFAULT_FACTORY = new EngineResourceFactory();
public synchronized void start(DecodeJob<R> decodeJob) {
this.decodeJob = decodeJob;
GlideExecutor executor =
decodeJob.willDecodeFromCache() ? diskCacheExecutor : getActiveSourceExecutor();
executor.execute(decodeJob);
}
engineJob.start(decodeJob);这里可以看到egineJob持有了decodeJob类，同时查看 executor.execute(decodeJob)方法,DecodeJob实现了Runable类，这里即为run方法：
@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) { // 失败
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) { // 失败
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();
}
}
这里针对状态进行回调，失败就notifyFailed方法，主要看下runWrapped方法：
private void runWrapped() {
switch (runReason) {
case INITIALIZE:
stage = getNextStage(Stage.INITIALIZE);
currentGenerator = getNextGenerator(); // 执行下一步
runGenerators();
break;
case SWITCH_TO_SOURCE_SERVICE:
runGenerators();
break;
case DECODE_DATA:
decodeFromRetrievedData();
break;
default:
throw new IllegalStateException("Unrecognized run reason: " + runReason);
}
}
// 不同的缓存策略
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);
}
}
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();
}
}
这里我们主要看runWrapped方法中调用decodeFromRetrievedData方法，顾名思义这个方法是去获取相关数据：
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);// 调用
} catch (GlideException e) {
e.setLoggingDetails(currentAttemptingKey, currentDataSource);
throwables.add(e);
}
if (resource != null) {
notifyEncodeAndRelease(resource, currentDataSource);
} else {
runGenerators();
}
}
这里 resource = decodeFromData(currentFetcher, currentData, currentDataSource)继续去请求调用resource资源，往下看notifyEncodeAndRelease方法即为去解析数据：
private void notifyEncodeAndRelease(Resource<R> resource, DataSource dataSource) {
if (resource instanceof Initializable) {
((Initializable) resource).initialize();
}
Resource<R> result = resource;
LockedResource<R> lockedResource = null;
if (deferredEncodeManager.hasResourceToEncode()) {
lockedResource = LockedResource.obtain(resource);
result = lockedResource;
}
notifyComplete(result, dataSource);
stage = Stage.ENCODE;
try {
if (deferredEncodeManager.hasResourceToEncode()) {
deferredEncodeManager.encode(diskCacheProvider, options);
}
} finally {
if (lockedResource != null) {
lockedResource.unlock();
}
}
// Call onEncodeComplete outside the finally block so that it's not called if the encode process
// throws.
onEncodeComplete();
}
deferredEncodeManager.encode(diskCacheProvider, options)可以看到这里主要是去解析数据：
@Synthetic
DeferredEncodeManager() {}
// We just need the encoder and resource type to match, which this will enforce.
@SuppressWarnings("unchecked")
<X> void init(Key key, ResourceEncoder<X> encoder, LockedResource<X> toEncode) {
this.key = key;
this.encoder = (ResourceEncoder<Z>) encoder;
this.toEncode = (LockedResource<Z>) toEncode;
}
void encode(DiskCacheProvider diskCacheProvider, Options options) {
GlideTrace.beginSection("DecodeJob.encode");
try { // 缓存数据
diskCacheProvider
.getDiskCache()
.put(key, new DataCacheWriter<>(encoder, toEncode, options));
} finally {
toEncode.unlock();
GlideTrace.endSection();
}
}
boolean hasResourceToEncode() {
return toEncode != null;
}
void clear() {
key = null;
encoder = null;
toEncode = null;
}
}
这里可以看到通过diskCacheProvider获取到diskCache后即把相关数据在磁盘缓存了起来，这里磁盘缓存已经调用完毕，而取磁盘缓存的时候即在上述switch分支中有runGenerators方法，其实这个过程在存磁盘之前，我们进入代码去查看：
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.
}
查看currentGenerator.startNext()方法,currentGenerator是DataFetcherGenerator类的实例，这里看DataFetcherGenerator的实现类ResourceCacheGenerator；
public boolean startNext() {
List<Key> sourceIds = helper.getCacheKeys();
if (sourceIds.isEmpty()) {
return false;
}
List<Class<?>> resourceClasses = helper.getRegisteredResourceClasses();
if (resourceClasses.isEmpty()) {
if (File.class.equals(helper.getTranscodeClass())) {
return false;
}
throw new IllegalStateException(
"Failed to find any load path from "
+ helper.getModelClass()
+ " to "
+ helper.getTranscodeClass());
}
while (modelLoaders == null || !hasNextModelLoader()) {
resourceClassIndex++;
if (resourceClassIndex >= resourceClasses.size()) {
sourceIdIndex++;
if (sourceIdIndex >= sourceIds.size()) {
return false;
}
resourceClassIndex = 0;
}
Key sourceId = sourceIds.get(sourceIdIndex);
Class<?> resourceClass = resourceClasses.get(resourceClassIndex);
Transformation<?> transformation = helper.getTransformation(resourceClass);
// PMD.AvoidInstantiatingObjectsInLoops Each iteration is comparatively expensive anyway,
// we only run until the first one succeeds, the loop runs for only a limited
// number of iterations on the order of 10-20 in the worst case.
currentKey =
new ResourceCacheKey( // NOPMD AvoidInstantiatingObjectsInLoops
helper.getArrayPool(),
sourceId,
helper.getSignature(),
helper.getWidth(),
helper.getHeight(),
transformation,
resourceClass,
helper.getOptions());
cacheFile = helper.getDiskCache().get(currentKey);
if (cacheFile != null) {
sourceKey = sourceId;
modelLoaders = helper.getModelLoaders(cacheFile);
modelLoaderIndex = 0;
}
}
loadData = null;
boolean started = false;
while (!started && hasNextModelLoader()) {
ModelLoader<File, ?> modelLoader = modelLoaders.get(modelLoaderIndex++);
loadData =
modelLoader.buildLoadData(
cacheFile, helper.getWidth(), helper.getHeight(), helper.getOptions());
if (loadData != null && helper.hasLoadPath(loadData.fetcher.getDataClass())) {
started = true;
loadData.fetcher.loadData(helper.getPriority(), this);
}
}
return started;
}
这里可以看到modelLoaders == null且 !hasNextModelLoader()的时候循环里面有这样一句代码 cacheFile = helper.getDiskCache().get(currentKey)，此时即从磁盘文件里面获取了相关缓存资源。
这里相关缓存的流程已经梳理完成，总结一下，主要有三个缓存的过程：
1 loadFromActiveResources使用了弱引用的Map集合进行缓存；
2 loadFromCache 使用LRU算法的LruResourceCache进行缓存；
3 磁盘进行缓存；
此时我们再回到DecodeJob类中，当数据都已经加载且已经准备好了，调用notifyComplete方法：
private void notifyComplete(Resource<R> resource, DataSource dataSource) {
setNotifiedOrThrow();
callback.onResourceReady(resource, dataSource);
}
这里会调用到onResourceReady，callBack是我们之前设置的回调，其实最终实现类即为ImageViewTarget类中：
@Override
public void onResourceReady(@NonNull Z resource, @Nullable Transition<? super Z> transition) {
if (transition == null || !transition.transition(resource, this)) {
setResourceInternal(resource);
} else {
//可能会有设置加载动画
maybeUpdateAnimatable(resource);
}
}
这里调用了setResourceInternal类去设置资源，这里面其实也有后面加载动画的调用：
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);
}
protected abstract void setResource(@Nullable Z resource);
setResource进行抽象了，继续去找ImageViewTarget的实现类，我们查看其中一个实现类DrawableImageViewTarget：
@Override
protected void setResource(@Nullable Drawable resource) {
view.setImageDrawable(resource);
}
即在此时对资源进行了设置。完成了整个图片数据的加载；
至此整个Glide的加载图片过程已经基本完成，接下来继续看下本篇我们使用到的一些相关类的UML图作为最后的总结：
零星瓢虫_001.png
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