RxJava flatmap：如何根据第一次调用的结果进行多次调用

Question

我有 2 个改装电话需要进行 A 和 B：

(A)：返回一个ArrayList

(B): 获取(A) 的结果，它是一个ArrayList。(B) 遍历 ArrayList 并使用每个进行改造调用并将结果数据组合成最终的 ArrayList 发送给我的订阅者 onNext()

我在语法正确时遇到了麻烦......例如，我试图返回 arAllMedia，但我下面的代码希望我返回一个 Observable。

ServiceFactory.createRetrofitService().getUserFollowing(sessionMgr.getAuthToken())
                .flatMap(new Func1<UserSelfFollows, Observable<? extends ArrayList<Media.MediaData>>>() {
                    @Override
                    public Observable<? extends ArrayList<Media.MediaData>> call(UserSelfFollows userSelfFollows) {

                        //make second requests based on response from First request to get all Users
                        ArrayList<Media.MediaData> arAllMedia = new ArrayList<>();
                        for(UserSelfFollows.UserDataFollows user : userSelfFollows.userdata){

                            Response <ResponseBody> response ;
                            Call <ResponseBody> call;
                            try {
                                call = ServiceFactory.createRetrofitService().getMediaOfUser(user.id,sessionMgr.getAuthToken());
                                response =  call.execute();
                            }catch(IOException ex){
                                return Observable.error(ex);
                            }

                            if (response.isSuccessful()) {

                                try {
                                    String str = responseHelper.streamToString( response.body().byteStream());
                                    Gson gson = new GsonBuilder().create();
                                    Media media = gson.fromJson(str, Media.class);

                                    arAllMedia.addAll(media.mediaData);

                                } catch (IOException e) {
                                    return Observable.error(e);
                                }
                            } else {
                                return Observable.error( new Exception(  responseHelper.getErrorString( response.errorBody().byteStream())) );
                            }
                        }
                        return Observable.just(arAllMedia);

                    }
                })
                .subscribeOn(Schedulers.newThread())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Subscriber<ArrayList<Media.MediaData>>() {
                    @Override
                    public final void onCompleted() {

                    }

                    @Override
                    public final void onError(Throwable e) {

                    }

                    @Override
                    public final void onNext(ArrayList<Media.MediaData> arMedia) {

                    }
                })

使用下面的Maxim建议，但它不会编译：

ServiceFactory.createRetrofitService().getUserFollowing(sessionMgr.getAuthToken())
                .flatMapIterable(new Func1<UserSelfFollows, Iterable<?>>() {
                    @Override
                    public Iterable<?> call(UserSelfFollows userSelfFollows) {
                        return userSelfFollows.userdata;
                    }
                })
                .concatMap(new Func1<UserSelfFollows.UserDataFollows, Observable<Media.MediaData>>() {
                    @Override
                    public Observable<Media.MediaData> call(UserSelfFollows.UserDataFollows user) {

                        return ServiceFactory.createRetrofitService().getMediaOfUser(user.id,sessionMgr.getAuthToken());
                    }
                });

Answer 1

你需要返回

Observable.just(arAllMedia)