Glide(二)Request队列管理

入口

上篇总结了下Glide利用fm和一个空Fragment 进行生命周期的管理，这里继续看load & into。不多说，上代码

// 上篇分析了with,继续看下 load & into
Glide.with(this).load("url").into(...);

1.1 load

public RequestBuilder<Drawable> load(@Nullable Object model) {
    return asDrawable().load(model);
  }

  public RequestBuilder<Drawable> asDrawable() {
    return as(Drawable.class);
  }

  // 实例一个RequestBuilder
  public <ResourceType> RequestBuilder<ResourceType> as(Class<ResourceType> resourceClass) {
    return new RequestBuilder<>(glide, this, resourceClass);
  }

  // RequestBuilder 构造中的 requestManager
   protected RequestBuilder(Glide glide, RequestManager requestManager,
      Class<TranscodeType> transcodeClass) {
    this.glide = glide;
    this.requestManager = requestManager;
    this.context = glide.getGlideContext();
    this.transcodeClass = transcodeClass;
    this.defaultRequestOptions = requestManager.getDefaultRequestOptions();
    this.transitionOptions = requestManager.getDefaultTransitionOptions(transcodeClass);
    this.requestOptions = defaultRequestOptions;
  }

2.1 into

public Target<TranscodeType> into(ImageView view) {
    // 主线程校验（涉及View刷新）
    Util.assertMainThread();
    // View 非空校验
    Preconditions.checkNotNull(view);

    RequestOptions requestOptions = this.requestOptions;
    if (!requestOptions.isTransformationSet()
        && requestOptions.isTransformationAllowed()
        && view.getScaleType() != null) {
     // 获取图片位置类型
      switch (view.getScaleType()) {
        case CENTER_CROP:
          requestOptions = requestOptions.clone().optionalCenterCrop();
          break;
        case CENTER_INSIDE:
          requestOptions = requestOptions.clone().optionalCenterInside();
          break;
        case FIT_CENTER:
        case FIT_START:
        case FIT_END:
          requestOptions = requestOptions.clone().optionalFitCenter();
          break;
        case FIT_XY:
          requestOptions = requestOptions.clone().optionalCenterInside();
          break;
        case CENTER:
        case MATRIX:
        default:
          // Do nothing.
      }
    }

    return into(context.buildImageViewTarget(view, transcodeClass), requestOptions);
  }

  // 继续看into
  private <Y extends Target<TranscodeType>> Y into(@NonNull Y target, RequestOptions options) {
    Util.assertMainThread();
    Preconditions.checkNotNull(target);
    if (!isModelSet) {
      throw new IllegalArgumentException("You must call #load() before calling #into()");
    }

    options = options.autoClone();
    // 根据target & options中的属性 build 一个 Request
    Request request = buildRequest(target, options);

    // target 与 request 绑定，这里复用之前的Request
    Request previous = target.getRequest();

    // 这里校验request 是否一致 previous
    //一致就回收掉request
    if (request.isEquivalentTo(previous)) {
      request.recycle();

      //这里的是校验 previous 执行情况。
      //begin内部机制:
      //如果正在运行，会保证不中断运行
      //如果完成则重新开始并提交
      //如果失败，重新开始
      if (!Preconditions.checkNotNull(previous).isRunning()) {
        previous.begin();
      }
      return target;
    }

    // 如果两个request 不一致，则删除旧的，更新requestManager中的tartget,requesr到set
    requestManager.clear(target);
    target.setRequest(request);

    // requestManager 添加请求到 RequestTracker中 Set<Request>
    requestManager.track(target, request);

    return target;
  }

2.2 上面不难看出新建的request通过requestManager 添加请求到 RequestTracker中，requestManager 维护了一个RequestTracker，可以做到根据生命周期来处理所有request

// 在生命周期回调中，对应targetTracker不同处理
@Override
  public void onStart() {
    resumeRequests();
    targetTracker.onStart();
  }

  @Override
  public void onStop() {
    pauseRequests();
    targetTracker.onStop();
  }

  @Override
  public void onDestroy() {
    targetTracker.onDestroy();
    for (Target<?> target : targetTracker.getAll()) {
      clear(target);
    }
    targetTracker.clear();
    requestTracker.clearRequests();
    lifecycle.removeListener(this);
    lifecycle.removeListener(connectivityMonitor);
    mainHandler.removeCallbacks(addSelfToLifecycle);
    glide.unregisterRequestManager(this);
  }

3.1 RequestManager中，requestTracker做为RequestManager成员变量被创建和初始化，所有request都由RequestManager加到了requestTracker中来管理，并与生命周期挂钩。看下requestTracker


public class RequestTracker {
  // 用set 防止未开始或者onPause的时候被GC干掉
  private final Set<Request> requests =
      Collections.newSetFromMap(new WeakHashMap<Request, Boolean>());

  @SuppressWarnings("MismatchedQueryAndUpdateOfCollection")
  private final List<Request> pendingRequests = new ArrayList<>();
  private boolean isPaused;

  /**
   * Starts tracking the given request.
   */
  public void runRequest(Request request) {
    requests.add(request);
    if (!isPaused) {
      request.begin();
    } else {
      pendingRequests.add(request);
    }
  }

  // Visible for testing.
  void addRequest(Request request) {
    requests.add(request);
  }

  /**
   * Stops tracking the given request, clears, and recycles it, and returns {@code true} if the
   * request was removed or {@code false} if the request was not found.
   */
  public boolean clearRemoveAndRecycle(Request request) {
    if (request == null) {
      return false;
    }
    boolean isOwnedByUs = requests.remove(request);
    // Avoid short circuiting.
    isOwnedByUs = pendingRequests.remove(request) || isOwnedByUs;
    if (isOwnedByUs) {
      request.clear();
      request.recycle();
    }
    return isOwnedByUs;
  }

  /**
   * Returns {@code true} if requests are currently paused, and {@code false} otherwise.
   */
  public boolean isPaused() {
    return isPaused;
  }

  /**
   * Stops any in progress requests.
   */
  public void pauseRequests() {
    isPaused = true;
    for (Request request : Util.getSnapshot(requests)) {
      if (request.isRunning()) {
        request.pause();
        pendingRequests.add(request);
      }
    }
  }

  /**
   * Starts any not yet completed or failed requests.
   */
  public void resumeRequests() {
    isPaused = false;
    for (Request request : Util.getSnapshot(requests)) {
      if (!request.isComplete() && !request.isCancelled() && !request.isRunning()) {
        request.begin();
      }
    }
    pendingRequests.clear();
  }

  /**
   * Cancels all requests and clears their resources.
   *
   * <p>After this call requests cannot be restarted.
   */
  public void clearRequests() {
    for (Request request : Util.getSnapshot(requests)) {
      clearRemoveAndRecycle(request);
    }
    pendingRequests.clear();
  }

  /**
   * Restarts failed requests and cancels and restarts in progress requests.
   */
  public void restartRequests() {
    for (Request request : Util.getSnapshot(requests)) {
      if (!request.isComplete() && !request.isCancelled()) {
        // Ensure the request will be restarted in onResume.
        request.pause();
        if (!isPaused) {
          request.begin();
        } else {
          pendingRequests.add(request);
        }
      }
    }
  }

  @Override
  public String toString() {
    return super.toString() + "{numRequests=" + requests.size() + ", isPaused=" + isPaused + "}";
  }
}

3.2 以上看出RequestTracker对所有Requst进行对应生命周期的维护
- 1. 比如onPause时，对所有Request暂停，加入set
- 1. onResume 时，对所有Request 进行restart
- 1. onStop 时，clear all Request
一波666

总结

主要对所有Request 进行队列维护，并在生命周期回调中进行相应优化
梳理了一下，看图比较直接

结构类图

Glide(二)Request队列管理

入口

总结

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