Glide 是如何获取ImageView的大小的？

草图镇楼 ff9d5505445322c03e69a5813aba596.jpg
d73b6e1e4bb97f712c627b00674d858.jpg

带着问题来看源码， Glide.with().load().into()之前的文章里面有说过with和load方法不涉及图片操作，所以就直接看into方法追踪源码可以看到into方法如下 传入Imageview 然后构建一个ImageviewTarget，
into(context.buildImageViewTarget(view, transcodeClass))

继续看into方法

  Request request = buildRequest(target);
    target.setRequest(request);
    requestManager.track(target, request);

是构建了一个request
继续追踪得到如下方法

  private Request buildRequestRecursive(Target<TranscodeType> target,
      @Nullable ThumbnailRequestCoordinator parentCoordinator,
      TransitionOptions<?, ? super TranscodeType> transitionOptions,
      Priority priority, int overrideWidth, int overrideHeight) {
    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;
      if (DEFAULT_ANIMATION_OPTIONS.equals(thumbTransitionOptions)) {
        thumbTransitionOptions = transitionOptions;
      }

      Priority thumbPriority = thumbnailBuilder.requestOptions.isPrioritySet()
          ? thumbnailBuilder.requestOptions.getPriority() : getThumbnailPriority(priority);

      int thumbOverrideWidth = thumbnailBuilder.requestOptions.getOverrideWidth();
      int thumbOverrideHeight = thumbnailBuilder.requestOptions.getOverrideHeight();
      if (Util.isValidDimensions(overrideWidth, overrideHeight)
          && !thumbnailBuilder.requestOptions.isValidOverride()) {
        thumbOverrideWidth = requestOptions.getOverrideWidth();
        thumbOverrideHeight = requestOptions.getOverrideHeight();
      }

      ThumbnailRequestCoordinator coordinator = new ThumbnailRequestCoordinator(parentCoordinator);
      Request fullRequest = obtainRequest(target, requestOptions, coordinator,
          transitionOptions, priority, overrideWidth, overrideHeight);
      isThumbnailBuilt = true;
      // Recursively generate thumbnail requests.
      Request thumbRequest = thumbnailBuilder.buildRequestRecursive(target, coordinator,
          thumbTransitionOptions, thumbPriority, thumbOverrideWidth, thumbOverrideHeight);
      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(parentCoordinator);
      Request fullRequest = obtainRequest(target, requestOptions, coordinator, transitionOptions,
          priority, overrideWidth, overrideHeight);
      RequestOptions thumbnailOptions = requestOptions.clone()
          .sizeMultiplier(thumbSizeMultiplier);

      Request thumbnailRequest = obtainRequest(target, thumbnailOptions, coordinator,
          transitionOptions, getThumbnailPriority(priority), overrideWidth, overrideHeight);

      coordinator.setRequests(fullRequest, thumbnailRequest);
      return coordinator;
    } else {
      // Base case: no thumbnail.
      return obtainRequest(target, requestOptions, parentCoordinator, transitionOptions, priority,
          overrideWidth, overrideHeight);
    }
  }

这里主要是判断是否设置缩略图，如果没有那么就直接调用最后那句 return obtianRequest(*****);
为了保持清晰，我们直接可以看这句 然后看下方法

  private Request obtainRequest(Target<TranscodeType> target,
      RequestOptions requestOptions, RequestCoordinator requestCoordinator,
      TransitionOptions<?, ? super TranscodeType> transitionOptions, Priority priority,
      int overrideWidth, int overrideHeight) {
    requestOptions.lock();

    return SingleRequest.obtain(
        context,
        model,
        transcodeClass,
        requestOptions,
        overrideWidth,
        overrideHeight,
        priority,
        target,
        requestListener,
        requestCoordinator,
        context.getEngine(),
        transitionOptions.getTransitionFactory());
  }

可以看到构造了一个SingleRequest，这里也就知道了 Request是SingleRequest的实现类
那么然后就继续看into方法 执行到了
requestManager.track(target, request);
内部是调用了

  public void runRequest(Request request) {
    requests.add(request);
    if (!isPaused) {
      request.begin();
    } else {
      pendingRequests.add(request);
    }
  }

直接看begin方法因为我们知道是SingleRequst，所以直接看SingleRequest类内部的begin，是调用了如下方法

@Override
  public void begin() {
    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;
    }

    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 (Log.isLoggable(TAG, Log.VERBOSE)) {
      logV("finished run method in " + LogTime.getElapsedMillis(startTime));
    }
  }

这里的model通过追踪可以得知，就是load方法传入的数据源对象，所以说就是判断数据源是否有效，所以我们直接往下看，假装他有效（2333），那么就开始了判断size是否可用，一开始没赋值，那么肯定是不可以用的，所以就是调用了target.getSize(this);方法，前面说过这里的target是构造出来的DrawableImageViewTarget然后看下他的getSize方法，发现没有，那么就往父类上找，最后发现是通过SizeDeterminer这个类来获取的，然后可以看到方法getSize，至此通过查看方法知道了Imageview的大小是如何得到了，通过layoutparams，Imageview的size，已经padding来得到的

总结

文章格式还需要继续改进，这里只是指引大家如何带着问题来查看源码一个过程，看源码不用太深入，重要是把流程走到位，熟悉流程了然后再来看内部仔细的实现，当然这里再看的时候也看到了很多的设计模式可以学习一下。