Glide源码解析四(解码和转码)

本文基于Glide 4.11.0

Glide加载过程有一个解码过程,比如将url加载为inputStream后,要将inputStream解码为Bitmap。

 

Glide源码解析一我们大致知道了Glide加载的过程,所以我们可以直接从这里看起,在这个过程中我们以从文件中加载bitmap为例:

DecodeJob的一个方法:

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();
  }
}

主要是这个方法:resource = decodeFromData(currentFetcher, currentData, currentDataSource);

这时候currentData为FileInputStream,因为我们加载的是本地文件。 

currentDateSource为LOCAL,即为本地的资源

 

 

 我们继续找下去

resource = decodeFromData(currentFetcher, currentData, currentDataSource);

----------------->

Resource<R> result = decodeFromFetcher(data, dataSource);

------------------>

private <Data> Resource<R> decodeFromFetcher(Data data, DataSource dataSource)
    throws GlideException {
  LoadPath<Data, ?, R> path = decodeHelper.getLoadPath((Class<Data>) data.getClass());
  return runLoadPath(data, dataSource, path);

这里获取到LoadPath的对象,我么先看看LoadPath有什么?

我们可以看到一个DecodePaths:

 

 DecodePath里面又保存着decoders

 

decoders便是我们需要的解码器,拿到解码器后就可以进行解码了。

那怎么拿到?

Glide源码解析三中我们知道这些解码器都注册在Register中,所以我们也是要通过它来拿:

<Data> LoadPath<Data, ?, Transcode> getLoadPath(Class<Data> dataClass) {
  return glideContext.getRegistry().getLoadPath(dataClass, resourceClass, transcodeClass);
}

---------------->

 

@Nullable
public <Data, TResource, Transcode> LoadPath<Data, TResource, Transcode> getLoadPath(
    @NonNull Class<Data> dataClass, @NonNull Class<TResource> resourceClass,
    @NonNull Class<Transcode> transcodeClass) {
  LoadPath<Data, TResource, Transcode> result =
      loadPathCache.get(dataClass, resourceClass, transcodeClass);
  if (loadPathCache.isEmptyLoadPath(result)) {
    return null;
  } else if (result == null) {
    List<DecodePath<Data, TResource, Transcode>> decodePaths =
        getDecodePaths(dataClass, resourceClass, transcodeClass);
    // It's possible there is no way to decode or transcode to the desired types from a given
    // data class.
    if (decodePaths.isEmpty()) {
      result = null;
    } else {
      result =
          new LoadPath<>(
              dataClass, resourceClass, transcodeClass, decodePaths, throwableListPool);
    }
    loadPathCache.put(dataClass, resourceClass, transcodeClass, result);
  }
  return result;
}

首先会先从缓存中拿,缓存中拿不到再通过下面的方法去拿:

List<DecodePath<Data, TResource, Transcode>> decodePaths = getDecodePaths(dataClass, resourceClass, transcodeClass);

 

private <Data, TResource, Transcode> List<DecodePath<Data, TResource, Transcode>> getDecodePaths(
    @NonNull Class<Data> dataClass, @NonNull Class<TResource> resourceClass,
    @NonNull Class<Transcode> transcodeClass) {
  List<DecodePath<Data, TResource, Transcode>> decodePaths = new ArrayList<>();
  List<Class<TResource>> registeredResourceClasses =
      decoderRegistry.getResourceClasses(dataClass, resourceClass);
  for (Class<TResource> registeredResourceClass : registeredResourceClasses) {
    List<Class<Transcode>> registeredTranscodeClasses =
        transcoderRegistry.getTranscodeClasses(registeredResourceClass, transcodeClass);
    for (Class<Transcode> registeredTranscodeClass : registeredTranscodeClasses) {
      List<ResourceDecoder<Data, TResource>> decoders =
          decoderRegistry.getDecoders(dataClass, registeredResourceClass);
      ResourceTranscoder<TResource, Transcode> transcoder =
          transcoderRegistry.get(registeredResourceClass, registeredTranscodeClass);
      @SuppressWarnings("PMD.AvoidInstantiatingObjectsInLoops")
      DecodePath<Data, TResource, Transcode> path =
          new DecodePath<>(dataClass, registeredResourceClass, registeredTranscodeClass,
              decoders, transcoder, throwableListPool);
      decodePaths.add(path);
    }
  }
  return decodePaths;
}

 该方法各个参数如下:

dataClass为InputStream,这是被解码的对象

 

resourceClass为Object,要解码成为Object

 

 

transcodeClass为Drawable,要转码为Drawable

我们看这个方法:

decoderRegistry.getResourceClasses:

 

public synchronized <T, R> List<Class<R>> getResourceClasses(@NonNull Class<T> dataClass,
    @NonNull Class<R> resourceClass) {
  List<Class<R>> result = new ArrayList<>();
  for (String bucket : bucketPriorityList) {
    List<Entry<?, ?>> entries = decoders.get(bucket);
    if (entries == null) {
      continue;
    }
    for (Entry<?, ?> entry : entries) {
      if (entry.handles(dataClass, resourceClass)
          && !result.contains((Class<R>) entry.resourceClass)) {
        result.add((Class<R>) entry.resourceClass);
      }
    }
  }
  return result;
}

该方法是为了获取解码器中的resourceClass,即解码后的资源类型。

我们可以看到decoder这个map里面的内容:

 

各种类型对应的解码器。

 

只有满足entry.handles(dataClass, resourceClass),才能被添加返回:

public boolean handles(@NonNull Class<?> dataClass, @NonNull Class<?> resourceClass) {
  return this.dataClass.isAssignableFrom(dataClass) && resourceClass
      .isAssignableFrom(this.resourceClass);
}

由于我们的resourceClass是Object,因此resourceClass .isAssignableFrom(this.resourceClass)总是成立的,所以就看:this.dataClass.isAssignableFrom(dataClass)

而我们的dataClass是InputStream,打开各种类型,可以看到哪些的dataClass是InputStream:

 

上面框错了,应该框resourceClass,另外FrameSequenceDrawable是我自定义后注册进去的,所以Glide原生的是没有的。

所以最终返回的resource为:

 

 

接下来是针对每一种resourceClass获取对应的转码类(要转成的对象):

public synchronized <Z, R> List<Class<R>> getTranscodeClasses(
    @NonNull Class<Z> resourceClass, @NonNull Class<R> transcodeClass) {
  List<Class<R>> transcodeClasses = new ArrayList<>();
  // GifDrawable -> Drawable is just the UnitTranscoder, as is GifDrawable -> GifDrawable.
  if (transcodeClass.isAssignableFrom(resourceClass)) {
    transcodeClasses.add(transcodeClass);
    return transcodeClasses;
  }
  for (Entry<?, ?> entry : transcoders) {
    if (entry.handles(resourceClass, transcodeClass)) {
      transcodeClasses.add(transcodeClass);
    }
  }
  return transcodeClasses;
}

如果transcodeClass是resourceClass的父类那就直接返回。

第一个GifDrawable,返回的registeredTranscodeClasses为:

 

 

然后根据dataClass, registeredResourceClass获取decoders:

 

 

然后根据registeredResourceClass和registeredTranscodeClass获取transcoder

 

上面具体的获取过程是类似的,就不过多分析了。

 

然后构造DecodePath,放进下面的集合里面:

List<DecodePath<Data, TResource, Transcode>> decodePaths = new ArrayList<>();

 

循环获取之后,最终得到的decodePaths如下:

 

 

大致流程:

1、先根据传进来的resourceClass获取注册表中所有注册的resourceClass得到List<Class<TResource>> registeredResourceClasses

2、两层for循环:

   (1)外层:根据registeredResourceClasses获取转码的class :List<Class<Transcode>> registeredTranscodeClasses

   (2)内层:

            a、根据资源resourceClass获取所有的解码器。

            b、根据资源resourceClass和转码transcodeClass获取所有的转码器。

            c、构造DecodePath,放进集合里面。

 

最后得到的List<DecodePath<Data, TResource, Transcode>> decodePaths被放到LoadPath对象里面(上一层方法可看到)

 

 我们又回到DecodeJob中的方法:

private <Data> Resource<R> decodeFromFetcher(Data data, DataSource dataSource)
    throws GlideException {
  LoadPath<Data, ?, R> path = decodeHelper.getLoadPath((Class<Data>) data.getClass());
  return runLoadPath(data, dataSource, path);
}

获取到LoadPath后接下来就是要开始执行了runLoadPath了。

 

找下去可以看到该方法:

return path.load(
          rewinder, options, width, height, new DecodeCallback<ResourceType>(dataSource));

该方法属于LoadPath对象。

 

层层追溯后,最终来到下面的方法:

private Resource<Transcode> loadWithExceptionList(DataRewinder<Data> rewinder,
    @NonNull Options options,
    int width, int height, DecodePath.DecodeCallback<ResourceType> decodeCallback,
    List<Throwable> exceptions) throws GlideException {
  Resource<Transcode> result = null;
  //noinspection ForLoopReplaceableByForEach to improve perf
  for (int i = 0, size = decodePaths.size(); i < size; i++) {
    DecodePath<Data, ResourceType, Transcode> path = decodePaths.get(i);
    try {
      result = path.decode(rewinder, width, height, options, decodeCallback);
    } catch (GlideException e) {
      exceptions.add(e);
    }
    if (result != null) {
      break;
    }
  }
  if (result == null) {
    throw new GlideException(failureMessage, new ArrayList<>(exceptions));
  }
  return result;
}

该方法在LoadPath里面,遍历decodePaths(这是我们之前获取后放在LoadPath中的)进行解码:

result = path.decode(rewinder, width, height, options, decodeCallback);

然后来到:

public Resource<Transcode> decode(DataRewinder<DataType> rewinder, int width, int height,
    @NonNull Options options, DecodeCallback<ResourceType> callback) throws GlideException {
  Resource<ResourceType> decoded = decodeResource(rewinder, width, height, options);
  Resource<ResourceType> transformed = callback.onResourceDecoded(decoded);
  return transcoder.transcode(transformed, options);
}

我们这里需要看的就是:decodeResource:

最终来到DecodePath里面的方法:

@NonNull
private Resource<ResourceType> decodeResourceWithList(DataRewinder<DataType> rewinder, int width,
    int height, @NonNull Options options, List<Throwable> exceptions) throws GlideException {
  Resource<ResourceType> result = null;
  //noinspection ForLoopReplaceableByForEach to improve perf
  for (int i = 0, size = decoders.size(); i < size; i++) {
    ResourceDecoder<DataType, ResourceType> decoder = decoders.get(i);
    try {
      DataType data = rewinder.rewindAndGet();
      if (decoder.handles(data, options)) {
        data = rewinder.rewindAndGet();
        result = decoder.decode(data, width, height, options);
      }
      // Some decoders throw unexpectedly. If they do, we shouldn't fail the entire load path, but
      // instead log and continue. See #2406 for an example.
    } catch (IOException | RuntimeException | OutOfMemoryError e) {
      if (Log.isLoggable(TAG, Log.VERBOSE)) {
        Log.v(TAG, "Failed to decode data for " + decoder, e);
      }
      exceptions.add(e);
    }
    if (result != null) {
      break;
    }
  }
  if (result == null) {
    throw new GlideException(failureMessage, new ArrayList<>(exceptions));
  }
  return result;
}

这个方法:decoder.handles(data, options)是判断该解码器是否可以对该资源进行解码,这个方法写在每个解码器里面。

DataRewinder里面放着需要进行解码的数据。

解码后将资源返回。

 

又回到这个方法:

public Resource<Transcode> decode(DataRewinder<DataType> rewinder, int width, int height,
    @NonNull Options options, DecodeCallback<ResourceType> callback) throws GlideException {
  Resource<ResourceType> decoded = decodeResource(rewinder, width, height, options);
  Resource<ResourceType> transformed = callback.onResourceDecoded(decoded);
  return transcoder.transcode(transformed, options);
}

这一句Resource<ResourceType> transformed = callback.onResourceDecoded(decoded);

是对资源进行变换处理,比如图片的缩放,剪裁等等,这个功能单独拎出来讲。

接下来便是运用转码器进行资源的转码:

transcoder.transcode(transformed, options)

 

到此就结束了。

 

转载请标明:https://www.cnblogs.com/tangZH/p/12912698.html

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