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yunshuipiao
yunshuipiao
Glide：The loading process of the main flow
Glide：The loading process of the main flow
[TOC]
分析来自 glide 4.8.0, 官方 使用文档
Glide是一个快速高效的Android图片加载库，注重于平滑的滚动。
Glide 支持拉取，解码和展示视频快照，图片，和GIF动画。
Glide.with(fragment) .load(url) .into(imageView);
上面是官网介绍的最简单的用法，本文章就对这个主流程做个简单分析。
.with()
首先来看 with 方法做了什么：
/*
* @param context Any context, will not be retained.
* @return A RequestManager for the top level application that can be used to start a load.
* @see #with(android.app.Activity)
* @see #with(android.app.Fragment)
* @see #with(android.support.v4.app.Fragment)
* @see #with(android.support.v4.app.FragmentActivity)
*/
@NonNull
public static RequestManager with(@NonNull Context context) {
return getRetriever(context).get(context);
}
@NonNull
public static RequestManager with(@NonNull View view) {
return getRetriever(view.getContext()).get(view);
}
// 最终调用
@NonNull
private static RequestManagerRetriever getRetriever(@Nullable Context context) {
// Context could be null for other reasons (ie the user passes in null), but in practice it will
// only occur due to errors with the Fragment lifecycle.
Preconditions.checkNotNull(
context,
"You cannot start a load on a not yet attached View or a Fragment where getActivity() "
+ "returns null (which usually occurs when getActivity() is called before the Fragment "
+ "is attached or after the Fragment is destroyed).");
return Glide.get(context).getRequestManagerRetriever();
}
with 有多个重载方法，最终都会调用上述方法, 最终返回一个 RequestManager 对象。这里传入的 context 必须要绑定 view，或者 fragment.getActivity() 不等于 null 。
@NonNull
public static Glide get(@NonNull Context context) {
if (glide == null) {
synchronized (Glide.class) {
if (glide == null) {
// 初始化 glide
checkAndInitializeGlide(context);
}
}
}
return glide;
}
private static void checkAndInitializeGlide(@NonNull Context context) {
// In the thread running initGlide(), one or more classes may call Glide.get(context).
// Without this check, those calls could trigger infinite recursion.
if (isInitializing) {
throw new IllegalStateException("You cannot call Glide.get() in registerComponents(),"
+ " use the provided Glide instance instead");
}
isInitializing = true;
// 初始化
initializeGlide(context);
isInitializing = false;
}
下面重点来看一下 初始化方法中具体做了什么：
private static void initializeGlide(@NonNull Context context) {
initializeGlide(context, new GlideBuilder());
}
/**
* A builder class for setting default structural classes for Glide to use.
* 建造者模式创建 Glide
*/
public final class GlideBuilder {
// 过渡方式
private final Map<Class<?>, TransitionOptions<?, ?>> defaultTransitionOptions = new ArrayMap<>();
// 负责加载和管理活跃和缓存的资源
private Engine engine;
// 重用的 bitmap 资源池
private BitmapPool bitmapPool;
// 不同数组类型的资源池
private ArrayPool arrayPool;
// 内存缓存
private MemoryCache memoryCache;
// 线程池，执行任务
private GlideExecutor sourceExecutor;
// 线程池，磁盘缓存
private GlideExecutor diskCacheExecutor;
// 懒加载创建磁盘缓存
private DiskCache.Factory diskCacheFactory;
// 缓存大小计算
private MemorySizeCalculator memorySizeCalculator;
// 网络连接监视器
private ConnectivityMonitorFactory connectivityMonitorFactory;
private int logLevel = Log.INFO;
// 自定义独立的请求选项，常用
private RequestOptions defaultRequestOptions = new RequestOptions();
@Nullable
// 创建 requestManager
private RequestManagerFactory requestManagerFactory;
private GlideExecutor animationExecutor;
private boolean isActiveResourceRetentionAllowed;
@Nullable
// 当图片记载时，监测请求状态
private List<RequestListener<Object>> defaultRequestListeners;
private boolean isLoggingRequestOriginsEnabled;
...
}
所以知道 Glide类中的属性大概有些什么，其中重要的资源池，请求和缓存，后续会介绍。
回到初始化的逻辑，内容有点长，在关键部分做了注释。
private static void initializeGlide(@NonNull Context context, @NonNull GlideBuilder builder) {
Context applicationContext = context.getApplicationContext();
// 是否通过注解生成了类： GeneratedAppGlideModuleImpl
GeneratedAppGlideModule annotationGeneratedModule = getAnnotationGeneratedGlideModules();
// 获取 meta 中定义的 GlideModule
List<com.bumptech.glide.module.GlideModule> manifestModules = Collections.emptyList();
if (annotationGeneratedModule == null || annotationGeneratedModule.isManifestParsingEnabled()) {
manifestModules = new ManifestParser(applicationContext).parse();
}
if (annotationGeneratedModule != null
&& !annotationGeneratedModule.getExcludedModuleClasses().isEmpty()) {
Set<Class<?>> excludedModuleClasses =
annotationGeneratedModule.getExcludedModuleClasses();
Iterator<com.bumptech.glide.module.GlideModule> iterator = manifestModules.iterator();
while (iterator.hasNext()) {
com.bumptech.glide.module.GlideModule current = iterator.next();
if (!excludedModuleClasses.contains(current.getClass())) {
continue;
}
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(TAG, "AppGlideModule excludes manifest GlideModule: " + current);
}
iterator.remove();
}
}
if (Log.isLoggable(TAG, Log.DEBUG)) {
for (com.bumptech.glide.module.GlideModule glideModule : manifestModules) {
Log.d(TAG, "Discovered GlideModule from manifest: " + glideModule.getClass());
}
}
RequestManagerRetriever.RequestManagerFactory factory =
annotationGeneratedModule != null
? annotationGeneratedModule.getRequestManagerFactory() : null;
builder.setRequestManagerFactory(factory);
for (com.bumptech.glide.module.GlideModule module : manifestModules) {
module.applyOptions(applicationContext, builder);
}
if (annotationGeneratedModule != null) {
annotationGeneratedModule.applyOptions(applicationContext, builder);
}
// 以上是 Generated API，编译时生成代码的部分，先跳过。
// 默认值赋值，创建glide
Glide glide = builder.build(applicationContext);
for (com.bumptech.glide.module.GlideModule module : manifestModules) {
try {
module.registerComponents(applicationContext, glide, glide.registry);
} catch (AbstractMethodError e) {
throw new IllegalStateException(
"Attempting to register a Glide v3 module. If you see this, you or one of your"
+ " dependencies may be including Glide v3 even though you're using Glide v4."
+ " You'll need to find and remove (or update) the offending dependency."
+ " The v3 module name is: " + module.getClass().getName(), e);
}
}
if (annotationGeneratedModule != null) {
annotationGeneratedModule.registerComponents(applicationContext, glide, glide.registry);
}
applicationContext.registerComponentCallbacks(glide);
Glide.glide = glide;
上面的配置中，MemorySizeCalculator 内存大小的计算比较重要。至此，生成了 glide，用作后续处理的单例。
接着返回一个 requestManagerRetriever， 看一下glide 的属性，大部分都在 builder 中见过。
public class Glide implements ComponentCallbacks2 {
private static final String DEFAULT_DISK_CACHE_DIR = "image_manager_disk_cache";
private static final String TAG = "Glide";
// 唯一单例
private static volatile Glide glide;
private static volatile boolean isInitializing;
private final Engine engine;
private final BitmapPool bitmapPool;
private final MemoryCache memoryCache;
// 提前填充如 bitmappool 的对象
private final BitmapPreFiller bitmapPreFiller;
private final GlideContext glideContext;
// 管理组件注册，以扩展或替换Glide的默认加载、解码和编码逻辑。
private final Registry registry;
private final ArrayPool arrayPool;
// 创建和销毁 RequestManger 的对象
private final RequestManagerRetriever requestManagerRetriever;
private final ConnectivityMonitorFactory connectivityMonitorFactory;
private final List<RequestManager> managers = new ArrayList<>();
private MemoryCategory memoryCategory = MemoryCategory.NORMAL;
...
}
继续往下，getRetriever(context).get(context);然后分别 get 不同对象获取 RequestManager。
@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)) {
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());
}
}
return getApplicationManager(context);
}
@NonNull
private RequestManager supportFragmentGet(
@NonNull Context context,
@NonNull FragmentManager fm,
@Nullable Fragment parentHint,
boolean isParentVisible) {
SupportRequestManagerFragment current =
getSupportRequestManagerFragment(fm, parentHint, isParentVisible);
RequestManager requestManager = current.getRequestManager();
if (requestManager == null) {
// TODO(b/27524013): Factor out this Glide.get() call.
Glide glide = Glide.get(context);
requestManager =
factory.build(
glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
current.setRequestManager(requestManager);
}
return requestManager;
}
@NonNull
private SupportRequestManagerFragment getSupportRequestManagerFragment(
@NonNull final FragmentManager fm, @Nullable Fragment parentHint, boolean isParentVisible) {
SupportRequestManagerFragment current =
(SupportRequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);
if (current == null) {
current = pendingSupportRequestManagerFragments.get(fm);
if (current == null) {
// 创建无UI fragment 管理 glide 的生命周期
current = new SupportRequestManagerFragment();
current.setParentFragmentHint(parentHint);
if (isParentVisible) {
current.getGlideLifecycle().onStart();
}
pendingSupportRequestManagerFragments.put(fm, current);
fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
handler.obtainMessage(ID_REMOVE_SUPPORT_FRAGMENT_MANAGER, fm).sendToTarget();
}
}
return current;
}
这里创建了一个无UI的SupportRequestManagerFragment， 使其内部的 RequestManager 可以结合生命周期，安全的开始，停止和管理 glide 请求。这种方法在很多地方都有用到，不明白可以继续看一下源码。
小结
在上面的分析中，做的工作主要有：
各种属性的初始化工作，创建 glide 单例 —> 获取请求管理 RequestManager对象， 同时绑定 Lifecycle， start，stop，destory 事件。
有了 RequestManager 对象，那么接下来可以看一下 load 方法做了什么。
.load()
也是有多个重载方法，基本支持所有的图片资源加载，看下面的注释；
public RequestBuilder<Drawable> load(@Nullable Bitmap bitmap) {
return asDrawable().load(bitmap);
}
public RequestBuilder<Drawable> load(@Nullable Drawable drawable) {
return asDrawable().load(drawable);
}
public RequestBuilder<Drawable> load(@Nullable String string) {
return asDrawable().load(string);
}
public RequestBuilder<Drawable> load(@Nullable Uri uri) {
return asDrawable().load(uri);
}
public RequestBuilder<Drawable> load(@Nullable File file) {
return asDrawable().load(file);
}
public RequestBuilder<Drawable> load(@RawRes @DrawableRes @Nullable Integer resourceId) {
return asDrawable().load(resourceId);
}
public RequestBuilder<Drawable> load(@Nullable URL url) {
return asDrawable().load(url);
}
public RequestBuilder<Drawable> load(@Nullable byte[] model) {
return asDrawable().load(model);
}
public RequestBuilder<Drawable> load(@Nullable Object model) {
return asDrawable().load(model);
通过调用 as(Drawable.class) 将传入的类型 decode 为 Drawable 对象。
@NonNull
@CheckResult
public RequestBuilder<Drawable> asDrawable() {
return as(Drawable.class);
}
@NonNull
@CheckResult
public <ResourceType> RequestBuilder<ResourceType> as(
@NonNull Class<ResourceType> resourceClass) {
return new RequestBuilder<>(glide, this, resourceClass, context);
}
@SuppressLint("CheckResult")
@SuppressWarnings("PMD.ConstructorCallsOverridableMethod")
protected RequestBuilder(
@NonNull Glide glide,
RequestManager requestManager,
Class<TranscodeType> transcodeClass,
Context context) {
this.glide = glide;
this.requestManager = requestManager;
// 转换对象类型
this.transcodeClass = transcodeClass;
this.context = context;
this.transitionOptions = requestManager.getDefaultTransitionOptions(transcodeClass);
this.glideContext = glide.getGlideContext();
// 请求监听器
initRequestListeners(requestManager.getDefaultRequestListeners());
apply(requestManager.getDefaultRequestOptions());
}
下面就开始 进入 load 步骤, 无论调用 load 的哪个重载方法，都会进入下面的代码：
@NonNull
private RequestBuilder<TranscodeType> loadGeneric(@Nullable Object model) {
// 加载对象赋值
this.model = model;
isModelSet = true;
return this;
}
这一步将需要加载的 对象 赋值给RequesBuild 的 model 对象，接着就到了最复杂 into 步骤。
.into()
该方法接收一个 ImageView 对象，将要加载的图片在 view 上显示出来。
加载图片的过程分为几步，下面分别从每一步开始分析。
into() 也是有好几个重载方法，在拿到 ImageView 对象之后，会调用以下方法生成 target 对象，这里就是
DrawableImageViewTarget 对象。
/**
* A factory responsible for producing the correct type of
* {@link com.bumptech.glide.request.target.Target} for a given {@link android.view.View} subclass.
*/
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)");
}
}
}
接着经过 into 的几个重载方法,
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()");
}
// 构建新的请求
Request request = buildRequest(target, targetListener, options, callbackExecutor);
// 老请求
Request previous = target.getRequest();
if (request.isEquivalentTo(previous)
&& !isSkipMemoryCacheWithCompletePreviousRequest(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).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);
requestManager.track(target, request);
return target;
第一阶段
在构建 新的请求中，最后会调用到此方法, 主要的注释如下：
private Request buildRequestRecursive(
Target<TranscodeType> target, // 上面提到的加载对象
@Nullable RequestListener<TranscodeType> targetListener, //记载监听
@Nullable RequestCoordinator parentCoordinator, // 协调多个请求
TransitionOptions<?, ? super TranscodeType> transitionOptions, // 过渡
Priority priority, // 记载优先级
int overrideWidth,
int overrideHeight,
BaseRequestOptions<?> requestOptions, // 加载可选配置
Executor callbackExecutor) { // 线程池
// Build the ErrorRequestCoordinator first if necessary so we can update parentCoordinator.
// 错误的请求选项，加载失败时显示，用法可配置。
ErrorRequestCoordinator errorRequestCoordinator = null;
if (errorBuilder != null) {
errorRequestCoordinator = new ErrorRequestCoordinator(parentCoordinator);
parentCoordinator = errorRequestCoordinator;
}
// 缩略图请求
Request mainRequest =
buildThumbnailRequestRecursive(
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(
target,
targetListener,
errorRequestCoordinator,
errorBuilder.transitionOptions,
errorBuilder.getPriority(),
errorOverrideWidth,
errorOverrideHeight,
errorBuilder,
callbackExecutor);
errorRequestCoordinator.setRequests(mainRequest, errorRequest);
return errorRequestCoordinator;
}
上面的配置都是 glide 支持的配置，支持 error 图片和 缩略图 显示。同样，主流程没有设置，那么最终 创建一个 SingleRequest 对象。
private Request obtainRequest(...
) {
return SingleRequest.obtain(...
}
到目前有了请求和target ，requestManager.track(target, request); 进行 生命周期管理,以及开始进行请求
synchronized void track(@NonNull Target<?> target, @NonNull Request request) {
targetTracker.track(target);
requestTracker.runRequest(request);
}
/**
* Starts tracking the given request.
*/
public void runRequest(@NonNull Request request) {
requests.add(request);
if (!isPaused) {
// singleRequest 开始请求, 见下分析
request.begin();
} else {
request.clear();
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Paused, delaying request");
}
pendingRequests.add(request);
}
}
@Override
public synchronized void begin() {
// 进行必要条件验证
assertNotCallingCallbacks();
stateVerifier.throwIfRecycled();
startTime = LogTime.getLogTime();
// 如果加载资源为空
if (model == null) {
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
width = overrideWidth;
height = overrideHeight;
}
// 作为备用的 drawable https://muyangmin.github.io/glide-docs-cn/doc/placeholders.html#%E5%90%8E%E5%A4%87%E5%9B%9E%E8%B0%83%E7%AC%A6fallback
int logLevel = getFallbackDrawable() == null ? Log.WARN : Log.DEBUG;
// 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");
}
// 请求状态完成，遇到在此请求时，从内存缓存中读取
if (status == Status.COMPLETE) {
onResourceReady(resource, DataSource.MEMORY_CACHE);
return;
}
// 等待确认图片加载大小
status = Status.WAITING_FOR_SIZE;
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
onSizeReady(overrideWidth, overrideHeight);
} else {
target.getSize(this);
}
// 加载占位图片
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));
}
}
当配置的大小确定， 则进入 onSizeReady(), 方法，接着会调用 Engine.load() 方法，返回一个 LoadStatus 对象.
该方法使用给定的参数开始加载，大概的流程如下：
检查当前使用的活跃资源，如果存在则使用；并且将新的不活跃的资源加入内存缓存；
如果内存缓存中存在，是直接使用；
检查正在加载的资源中是否存在，如果存在则返回；
否则开始新的加载。
注：这里的活跃资源是指至少提供给一个请求并且还没有为回收的资源。如果所有使用者都释放了资源，将会进入缓存；这时如果从缓存中被重新使用，那么又会加入活跃资源中；如果资源从缓存中移除，那么资源会被重新利用，也可能被丢弃。没有严格要求释放资源，所以活跃的资源都很不稳定。
public synchronized <R> LoadStatus load(
GlideContext glideContext,
Object model,
Key signature, // 签名
int width,
int height,
Class<?> resourceClass,
Class<R> transcodeClass,
Priority priority,
DiskCacheStrategy diskCacheStrategy, //磁盘缓存策略
Map<Class<?>, Transformation<?>> transformations,
boolean isTransformationRequired,
boolean isScaleOnlyOrNoTransform,
Options options,
boolean isMemoryCacheable,
boolean useUnlimitedSourceExecutorPool,
boolean useAnimationPool,
boolean onlyRetrieveFromCache,
ResourceCallback cb, //加载成功的回调
Executor callbackExecutor) {
long startTime = VERBOSE_IS_LOGGABLE ? LogTime.getLogTime() : 0;
// 多个属性生成的，用于存储资源的key值
EngineKey key = keyFactory.buildKey(model, signature, width, height, transformations,
resourceClass, transcodeClass, options);
EngineResource<?> active = loadFromActiveResources(key, isMemoryCacheable);
if (active != null) {
// 从活跃资源中加载
cb.onResourceReady(active, DataSource.MEMORY_CACHE);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Loaded resource from active resources", startTime, key);
}
return null;
}
EngineResource<?> cached = loadFromCache(key, isMemoryCacheable);
if (cached != null) {
// 从内存缓存中加载
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) {
// 正在有请求加载中
current.addCallback(cb, callbackExecutor);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Added to existing load", startTime, key);
}
return new LoadStatus(cb, current);
}
// 创建加载请求job
EngineJob<R> engineJob =
engineJobFactory.build(
key,
isMemoryCacheable,
useUnlimitedSourceExecutorPool,
useAnimationPool,
onlyRetrieveFromCache);
// 解码资源的 job
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);
}
上面方法中涉及两个类，一个是 DecodeJob、一个是 EngineJob。它们之间的关系是，EngineJob 内部维护了线程池，用来管理资源加载，已经当资源加载完毕的时候通知回调。 DecodeJob 继承了 Runnable，是线程池当中的一个任务。就像上面那样，我们通过调用 engineJob.start(decodeJob) 来开始资源加载。
####小结
在第一阶段中，整体还是比较清晰。 首先创建的 SingleRequest，然后 RequestMangenr 对 target 和 request 进行管理， 生命周期和加入请求队列；
接着开始 request，会调用 Engine.load() 方法来决定从活跃资源，或者缓存，或者新建 DecodeJob 中加载资源。
第二阶段
decodeJob 将会将会开始执行，并将结果回调给 cb。因为 DecodeJob 继承了 Runnable， 所以会执行其 run 方法。
engineJob.addCallback(cb, callbackExecutor);
engineJob.start(decodeJob);
public synchronized void start(DecodeJob<R> decodeJob) {
this.decodeJob = decodeJob;
GlideExecutor executor = decodeJob.willDecodeFromCache()
? diskCacheExecutor
: getActiveSourceExecutor();
executor.execute(decodeJob);
}
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) {
// 主要过程在上面的 runWrapper(), 这里是为了捕获和处理 OOM 异常，图片操作不可避免。
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(TAG, "DecodeJob threw unexpectedly"
+ ", isCancelled: " + isCancelled
+ ", stage: " + stage, t);
}
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();
}
DecodeJob 的执行过程使用了状态模式，它会根据当前的状态决定将要执行的方法。在上面的方法中，当当前任务没有被取消的话，会进入到 runWrapped() 方法。该方法中会使用 runReason作为当前的状态决定要执行的逻辑：
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);
}
}
这里的 runReason 是一个枚举类型，它包含的枚举值即为上面的三种类型。当我们在一个过程执行完毕之后会回调 DecodeJob 中的方法修改 runReason，然后根据新的状态值执行新的逻辑。
除了 runReason，DecodeJob 中还有一个变量 stage 也是用来决定 DecodeJob 状态的变量。同样，它也是一个枚举，用来表示将要加载数据的数据源以及数据的加载状态。它主要在加载数据的时候在 runGenerators()、runWrapped() 和 getNextStage() 三个方法中被修改。通常它的逻辑是，先从（大小、尺寸等）转换之后的缓存中拿数据，如果没有的话再从没有转换过的缓存中拿数据，最后还是拿不到的话就从原始的数据源中加载数据。
以上就是 DecodeJob 中的状态模式运行的原理。
在上面的逻辑中，从 INITIALIZE 状态开始，由于这是没有设计到缓存，所以 得到 SourceGenerator,
currentGenerator.startNext())
@Override
public boolean startNext() {
if (dataToCache != null) {
Object data = dataToCache;
dataToCache = null;
// 加入cache
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;
// 加载资源
loadData.fetcher.loadData(helper.getPriority(), this);
}
}
return started;
}
由于这是加载的是网络上的资源，默认情况下会使用 HttpUrlFetcher 下载数据：
public void loadData(@NonNull Priority priority,
@NonNull DataCallback<? super InputStream> callback) {
long startTime = LogTime.getLogTime();
try {
// 获取输入流
InputStream result = loadDataWithRedirects(glideUrl.toURL(), 0, null, glideUrl.getHeaders());
// 回调结果
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 {
// 重定向过多
if (redirects >= MAXIMUM_REDIRECTS) {
throw new HttpException("Too many (> " + MAXIMUM_REDIRECTS + ") redirects!");
} else {
// Comparing the URLs using .equals performs additional network I/O and is generally broken.
// See http://michaelscharf.blogspot.com/2006/11/javaneturlequals-and-hashcode-make.html.
try {
if (lastUrl != null && url.toURI().equals(lastUrl.toURI())) {
throw new HttpException("In re-direct loop");
}
} catch (URISyntaxException e) {
// Do nothing, this is best effort.
}
}
// 网络下载流程
urlConnection = connectionFactory.build(url);
for (Map.Entry<String, String> headerEntry : headers.entrySet()) {
urlConnection.addRequestProperty(headerEntry.getKey(), headerEntry.getValue());
}
urlConnection.setConnectTimeout(timeout);
urlConnection.setReadTimeout(timeout);
urlConnection.setUseCaches(false);
urlConnection.setDoInput(true);
// Stop the urlConnection instance of HttpUrlConnection from following redirects so that
// redirects will be handled by recursive calls to this method, loadDataWithRedirects.
urlConnection.setInstanceFollowRedirects(false);
// Connect explicitly to avoid errors in decoders if connection fails.
urlConnection.connect();
// 获得流，防止资源泄漏
stream = urlConnection.getInputStream();
if (isCancelled) {
return null;
}
final int statusCode = urlConnection.getResponseCode();
if (isHttpOk(statusCode)) {
// 成功返回结果
return getStreamForSuccessfulRequest(urlConnection);
} else if (isHttpRedirect(statusCode)) {
// 重定向， 获取 地址继续请求
String redirectUrlString = urlConnection.getHeaderField("Location");
if (TextUtils.isEmpty(redirectUrlString)) {
throw new HttpException("Received empty or null redirect url");
}
URL redirectUrl = new URL(url, redirectUrlString);
// Closing the stream specifically is required to avoid leaking ResponseBodys in addition
// to disconnecting the url connection below. See #2352.
cleanup();
return loadDataWithRedirects(redirectUrl, redirects + 1, url, headers);
} else if (statusCode == INVALID_STATUS_CODE) {
throw new HttpException(statusCode);
} else {
throw new HttpException(urlConnection.getResponseMessage(), statusCode);
}
小结
这里涉及到 DecodeJob 的执行，和网络的请求过程，代码量相对较大的部分。因此也只是一个简单的分析，多看源码，多思考。下一阶段是将输入流转换成 Drawable。
第三阶段
上面的阶段结束，会回调 onDataReady() 方法：
@Override
public void onDataReady(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);
}
}
glide 有默认磁盘缓存策略，所以这里会执行：cb.reschedule();, 最后又回到 DecodeJob 的run 方法。
@Override
public void reschedule() {
runReason = RunReason.SWITCH_TO_SOURCE_SERVICE;
callback.reschedule(this);
}
private void cacheData(Object dataToCache) {
long startTime = LogTime.getLogTime();
try {
Encoder<Object> encoder = helper.getSourceEncoder(dataToCache);
DataCacheWriter<Object> writer =
new DataCacheWriter<>(encoder, dataToCache, helper.getOptions());
originalKey = new DataCacheKey(loadData.sourceKey, helper.getSignature());
//写入磁盘缓存
helper.getDiskCache().put(originalKey, writer);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Finished encoding source to cache"
+ ", key: " + originalKey
+ ", data: " + dataToCache
+ ", encoder: " + encoder
+ ", duration: " + LogTime.getElapsedMillis(startTime));
}
} finally {
loadData.fetcher.cleanup();
}
这里的主要逻辑是构建一个用于将数据缓存到磁盘上面的 DataCacheGenerator。DataCacheGenerator 的流程基本与 SourceGenerator 一致，也就是根据资源文件的类型找到 ModelLoader，然后使用 DataFetcher 加载缓存的资源。与之前不同的是，这次是用 DataFecher 来加载 File 类型的资源。也就是说，当我们从网络中拿到了数据之后 Glide 会先将其缓存到磁盘上面，然后再从磁盘上面读取图片并将其显示到控件上面。所以，当从网络打开了输入流之后 SourceGenerator 的任务基本结束了，而后的显示的任务都由 DataCacheGenerator 来完成。
DataCacheGenerator 中使用 DataUrlLoader.loadData() 后，回调 onDataReady（） 方法，接着会调用到：
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 {
// 获取数据，一直下去有很多方法
resource = decodeFromData(currentFetcher, currentData, currentDataSource);
} catch (GlideException e) {
e.setLoggingDetails(currentAttemptingKey, currentDataSource);
throwables.add(e);
}
if (resource != null) {
notifyEncodeAndRelease(resource, currentDataSource);
} else {
runGenerators();
}
}
这一阶段执行完毕，主要是 获取输入流之后的 处理过程，到达下一阶段。
第四阶段
notifyEncodeAndRelease(resource, currentDataSource);
方法一路往下追，最后回到SingleRequest,
private synchronized void onResourceReady(Resource<R> resource, R result, DataSource dataSource) {
.......
.......
.........
if (!anyListenerHandledUpdatingTarget) {
Transition<? super R> animation =
animationFactory.build(dataSource, isFirstResource);
// target 加载显示图片
target.onResourceReady(result, animation);
}
} finally {
isCallingCallbacks = false;
}
// 通知结束
notifyLoadSuccess();
}
然后 回调 ImageViewTarget 的方法， 整个过程结束。
@Override
public void onResourceReady(@NonNull Z resource, @Nullable Transition<? super Z> transition) {
if (transition == null || !transition.transition(resource, this)) {
setResourceInternal(resource);
} else {
maybeUpdateAnimatable(resource);
}
}
@Override
protected void setResource(@Nullable Drawable resource) {
view.setImageDrawable(resource);
}
总结
以上就是 Glide.with(fragment).into(ImageView) 的主流程的分析，大致步骤就是初始化 glide，创建 RequestManager， 接着创建出加载的类型 RequestBuild<Drawable> 的 model 对象。
在 into 过程中，主要有以下几步：
第一个阶段是开启 DecodeJob 的过程。DecodeJob 负责从缓存或者从原始的数据源中加载图片资源，对图片进行变换和转码，是 Glide 图片加载过程的核心。DecodeJob 继承了 Runnable，实际进行图片加载的时候会将其放置到线程池当中执行。这个阶段我们重点介绍的是从 RequestBuilder 构建一个 DecodeJob 并开启 DecodeJob 任务的过程。即构建一个 DecodeJob 并将其丢到线程池里的过程。
第二个阶段是打开网络流的过程。这个阶段会根据我们的图片资源来从数据源中加载图片数据。以我们的示例为例，在默认情况下会从网络当中加载图片，并得到一个 InputStream.
第三个阶段是将输入流转换为 Drawable 的过程。得到了 InputStream 之后还要调用 BitmapFactory 的 decodeStream() 方法来从 InputStream 中得到一个 Drawable.
第四个阶段是将 Drawable 显示到 ImageView 上面的过程。
其中最重要并且最负责的是中间两步，这篇文章只是提了个大概，后续会详细的分析。
当然，关于 Glide 还有很多没有谈到， 包括可配置的 RequestOptions，缓存，注解时生成的部分，希望后面有时间慢慢从用法到源码，慢慢了解吧。
