如何将多个请求与 rxjava2 正确组合？

Question

rxjava2 是否可以实现下面描述的序列？我有这样的课程：

class Holder {
    List<Image> images;
}
class Image {
    String url;
    String localFileUrl;
}

我需要一个类似的序列：

* Iterate over Holders;
  * For each Holder iterate over Images;
    * Working with each images(decode Bitmap from localFileUrl and upload 
     bitmap to network -> get url for image from network -> write url to 
     Image's file url);
* After iterating over all Holders(on this step all images inside Holders
 should have filled url), make upload for Holders;

我尝试过类似的方法：

Observable.fromIterable(holders)
  .concatMap(holder -> {
    Observable.fromIterable(holder.images)
      .concatMap(image -> {
        // decode bitmap here
        uploadImage(bitmap)
      })
  })
// what should I do here to get observable which emits holders,
// not result from uploadImage(bitmap)?
  .toList()
  .flatMap(? -> uploadeHolders());

是否可以迭代数据，对数据的每个项目执行一些操作，并对准备好的数据做一些工作（对每个项目执行操作）？

Answer 1

类似的东西-

Observable.fromIterable(holders)
  .concatMap(holder -> {
    Observable.fromIterable(holder.images)
      .flatMap(image -> {
        // decode bitmap here
        uploadImage(bitmap)
        .map(url -> {
          image.url = url;
          return image;
        });
      })
      .toList()
      .map(list -> {
        holder.images = list;
        return holder;
      });
  })
  .toList(); // optional, if you need holders as a list