Glide 执行流程分析

Arrom
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这是我参与11月更文挑战的第10天，活动详情查看：2021最后一次更文挑战

Glide调用流程

val requestManager = Glide.with(this);

val requestBuilder = requestManager.load("");

val target = requestBuilder.into(imageView)
  1. 调用Glide.with(this)创建一个RequestManager对象。
  2. requestManager对象load一个图片URL返回RequestBuilder对象（其范型类型为Drawable）。
  3. requestBuilder调用into方法使注入的ImageView显示对应url的图片

RequestManager的创建流程

构建RequestManager的过程，是Glide通过调用with方法返回的（以Activity为参数）。

@NonNull
public static RequestManager with(@NonNull Activity activity) {
  return getRetriever(activity).get(activity);
}

进入getRetriever方法

@NonNull
private static RequestManagerRetriever getRetriever(@Nullable Context context) {
  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();
}

返回一个RequestManagerRetriever对象，所以RequestManager对象是RequestManagerRetriever来构建的。
先看看glide的get方法：

public static Glide get(@NonNull Context context) {
  if (glide == null) {
    GeneratedAppGlideModule annotationGeneratedModule =
        getAnnotationGeneratedGlideModules(context.getApplicationContext());
    synchronized (Glide.class) {
      if (glide == null) {
        checkAndInitializeGlide(context, annotationGeneratedModule);
      }
    }
  }

  return glide;
}

checkAndInitializeGlide方法内部调用initializeGlide()方法类初始化Glide。

private static void initializeGlide(
    @NonNull Context context,
    @NonNull GlideBuilder builder,
    @Nullable GeneratedAppGlideModule annotationGeneratedModule) {
   ...
   //初始化Glide持有的RequestManagerRetriever对象
  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);
  }
  Glide glide = builder.build(applicationContext);
  for (com.bumptech.glide.module.GlideModule module : manifestModules) {
    try {
      module.registerComponents(applicationContext, glide, glide.registry);
    } catch (AbstractMethodError e) {
     
    }
  }
  if (annotationGeneratedModule != null) {
    annotationGeneratedModule.registerComponents(applicationContext, glide, glide.registry);
  }
  applicationContext.registerComponentCallbacks(glide);
  //新建glide
  Glide.glide = glide;
}

可以看出Glide的RequestManagerRetriever初始化也很简单，另外需要注意的是该对象需要一个requestManagerFactory对象，如果requestManagerFactory对象客户端没有设置的话则使用glide默认的对象。

public RequestManagerRetriever(
    @Nullable RequestManagerFactory factory, GlideExperiments experiments) {
  this.factory = factory != null ? factory : DEFAULT_FACTORY;
  handler = new Handler(Looper.getMainLooper(), this /* Callback */);

  frameWaiter = buildFrameWaiter(experiments);
}

默认的RequestManagerFactory的DEFAULT_FACTORY

private static final RequestManagerFactory DEFAULT_FACTORY =
    new RequestManagerFactory() {
      @NonNull
      @Override
      public RequestManager build(
          @NonNull Glide glide,
          @NonNull Lifecycle lifecycle,
          @NonNull RequestManagerTreeNode requestManagerTreeNode,
          @NonNull Context context) {
        return new RequestManager(glide, lifecycle, requestManagerTreeNode, context);
      }
    };

到此为止RequestManagerRetriever对象已经构建完毕，上文提到是通过RequestManagerRetriever对象的get方法来获取RequestManger对象的，所以让我们看看其get方法都做了些神马：

public RequestManager get(@NonNull Activity activity) {
  if (Util.isOnBackgroundThread()) {
    return get(activity.getApplicationContext());
  } else if (activity instanceof FragmentActivity) {
    return get((FragmentActivity) activity);
  } else {
    assertNotDestroyed(activity);
    frameWaiter.registerSelf(activity);
    android.app.FragmentManager fm = activity.getFragmentManager();
    return fragmentGet(activity, fm, /*parentHint=*/ null, isActivityVisible(activity));
  }
}

进入fragmentGet方法来看RequestManager的创建过程

private RequestManager fragmentGet(
    @NonNull Context context,
    @NonNull android.app.FragmentManager fm,
    @Nullable android.app.Fragment parentHint,
    boolean isParentVisible) {
  RequestManagerFragment current = getRequestManagerFragment(fm, parentHint);
  RequestManager requestManager = current.getRequestManager();
  if (requestManager == null) {
  //初始化RequestManager
    Glide glide = Glide.get(context);
    requestManager =
        factory.build(
            glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
    if (isParentVisible) {
      requestManager.onStart();
    }
    current.setRequestManager(requestManager);
  }
  return requestManager;
}

也就是说第一次初始化的时候调用上所说的工厂类DEFAULT_FACTORY来创建RequestManager.再次使用的话就是从RequestManagerFragment对象中获取了。

分析道这儿RequestManager对象的构建步骤分析完毕，总结下来也就是：

  1. Glide初始化的时候先创建一个RequestManagerRetriever对象，并且该对象持有一个构建RequestManager对象的工厂接口RequestManagerFactory。该接口客户端可以使用自己的实现来构建RequestManager对象，也可以使用Glide 默认的工厂接口实现类DEFAULT_FACTORY。
  2. 通过RequestManagerRetriever的get方法来初始化RequestManager,说白了就是调用factory的build方法来完成RequestManager的构建。

RequestBuilder的创建流程

//requestManager的load方法
public RequestBuilder<Drawable> load(@Nullable String string) {
  return asDrawable().load(string);
}
//asDrawable
public RequestBuilder<Drawable> asDrawable() {
  return as(Drawable.class);
}

public <ResourceType> RequestBuilder<ResourceType> as(
    @NonNull Class<ResourceType> resourceClass) {
  return new RequestBuilder<>(glide, this, resourceClass, context);
}

load最终先调用asDrawable方法，然后调用as 方法将RequestBuidler的范型设置为Drawable并new一个RequestBuilder对象。

protected RequestBuilder(
    @NonNull Glide glide,
    RequestManager requestManager,
    Class<TranscodeType> transcodeClass,
    Context context) {
  this.glide = glide;
  this.requestManager = requestManager;
  //在本文中为Drawable.class
  this.transcodeClass = transcodeClass;
  this.context = context;
  //获取默认的TransitionOptions对象
  this.transitionOptions = requestManager.getDefaultTransitionOptions(transcodeClass);
  this.glideContext = glide.getGlideContext();

  initRequestListeners(requestManager.getDefaultRequestListeners());
  apply(requestManager.getDefaultRequestOptions());
}

asDrawable方法调用完毕后就调用load(model)方法。

public RequestBuilder<TranscodeType> load(@Nullable String string) {
  return loadGeneric(string);
}
//loadGeneric
private RequestBuilder<TranscodeType> loadGeneric(@Nullable Object model) {
  if (isAutoCloneEnabled()) {
    return clone().loadGeneric(model);
  }
  this.model = model;
  isModelSet = true;
  return selfOrThrowIfLocked();
}

load 方法进而调用了loadGeneric方法，该方法就是设置了model属性（再此可以看为图片的url)和isModelSet变量。

到此为止RequestBuilder对象也就构建完毕了

ViewTarget的简单说明

public ViewTarget<ImageView, TranscodeType> into(@NonNull ImageView view) {
 //省略对图片设置参数的处理代码

  return into(
      glideContext.buildImageViewTarget(view, transcodeClass),
      /*targetListener=*/ null,
      requestOptions,
      Executors.mainThreadExecutor());
}

into方法最终调用了另外一个into重载方法，在调用重载方法之前先调用GlideContext对象的buildImageViewTarget方法,在Glide通过GlideBuilder调用Glide构造器创建的时候，在Glide构造器内部初始化来GlideContext对象。

//创建ImageViewTargetFactory对象
ImageViewTargetFactory imageViewTargetFactory = new ImageViewTargetFactory();
//初始化GlideContext对象
glideContext =
    new GlideContext(
        context,
        arrayPool,
        registry,
        imageViewTargetFactory,
        defaultRequestOptionsFactory,
        defaultTransitionOptions,
        defaultRequestListeners,
        engine,
        experiments,
        logLevel);

GlideContext的buildImageViewTarget

@NonNull
public <X> ViewTarget<ImageView, X> buildImageViewTarget(
    @NonNull ImageView imageView, @NonNull Class<X> transcodeClass) {
  return imageViewTargetFactory.buildTarget(imageView, transcodeClass);
}

调用了ImageViewTargetFactory来创建一个Target

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 {
   
  }
}

因为上文我们传的是Drawable,所以此时的工厂类返回的是一个DrawableImageViewTarget对象，该对象持有一个目标ImageView的引用。buildImageViewTarget调用完毕后紧接着将生成的target对象交给了into重载方法

public <Y extends Target<TranscodeType>> Y into(@NonNull Y target) {
  return into(target, /*targetListener=*/ null, Executors.mainThreadExecutor());
}

该into重载方法继而有调用了另外一个重载方法：

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()");
  }

  Request request = buildRequest(target, targetListener, options, callbackExecutor);

  Request previous = target.getRequest();
  if (request.isEquivalentTo(previous)
      && !isSkipMemoryCacheWithCompletePreviousRequest(options, previous)) {
    if (!Preconditions.checkNotNull(previous).isRunning()) {
      previous.begin();
    }
    return target;
  }

  requestManager.clear(target);
  target.setRequest(request);
  requestManager.track(target, request);

  return target;
}

此into方法调用完毕，该方法执行的结果是返回一个Target接口的实现类，Glide本身提供类各种Target实现类。

Request对象的创建

先构建了RequestBuilder对象，根据其名称我们可以猜出RequestBuilder对象的作用就是创建Ruquest对象，在最后一个into方法调用的时候调用了如下代码来构建Request对象

Request request = buildRequest(target, targetListener, options, callbackExecutor);

Glide中Request是一个接口。

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);
}

进入buildRequestRecursive方法

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) {

  ErrorRequestCoordinator errorRequestCoordinator = null;
  if (errorBuilder != null) {
    errorRequestCoordinator = new ErrorRequestCoordinator(requestLock, parentCoordinator);
    parentCoordinator = errorRequestCoordinator;
  }

  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;
}

进入buildThumbnailRequestRecursive方法

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) {
    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;

    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;
    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) {
    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 {
    return obtainRequest(
        requestLock,
        target,
        targetListener,
        requestOptions,
        parentCoordinator,
        transitionOptions,
        priority,
        overrideWidth,
        overrideHeight,
        callbackExecutor);
  }
}

进入obtainRequest方法，返回一个SingleRequest对象。

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);
}

Glide的大致工作流程

  1. 通过GlideBuilder来构建Glide对象
  2. 构建Glide对象的时候创建RequestManagerRetriever对象
  3. 通过RequestManangerRetriever对象持有的工厂类requestManagerFactory来构建RequestManager对象。
  4. RequestManager调用load方法构建一个RequestBuilder对象
  5. RequestBuilder对象在调用into方法的时候会调用buildRequest对象来build一个Request对象，同时会into方法会通过ImageViewTargetFactory工厂类来返回一个具体的Target对象。
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