Android：在MVVM中使用Transformations.switchMap进行顺序调用

我尝试对网络进行两次连续调用，其中第二次调用的参数是第一次调用的结果。我正在尝试使用MVVM和Transformations.switchMap执行此操作，但遇到异常“java.lang.IllegalArgumentException:无法为com.rdev.image.obj.flickresultsize类创建调用适配器”。有人知道怎么做吗

public LiveData<ArrayList<String>> getValuesAPI(String url) {

    LiveData<ArrayList<String>> ids = AbsentLiveData.create();
    LiveData<ArrayList<String>> urls = AbsentLiveData.create();
    final MutableLiveData<ArrayList<String>> updatedResult = new MediatorLiveData<>();

    //This method waits until it has the data to process
    ids = Transformations.switchMap(getValues(url), apiResponse-> {
        ArrayList<String> listaIds = new ArrayList<>();

        if(apiResponse.isSuccessful()) {

            if (apiResponse.body != null) {

                FlickrPhotos flickrPhotos = new FlickrPhotos();
                flickrPhotos = apiResponse.body.getPhotos();
                FlickrResultSize flickrResultSizes = new FlickrResultSize();

                for(int i=0;i<flickrPhotos.getPhoto().size();i++){
                    String id = flickrPhotos.getPhoto().get(i).getId();

                    String link = Utils.createURL(2,id);

                    flickrResultSizes = getPhotos(link); -----------I want to call this, but I can't
                    Timber.d("depois do getPhotos");
                    listaIds.add(id);


                }

                updatedResult.postValue(listaIds);
            }

        }
    });

  return ids;
}

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@有什么建议吗？@commonware有什么建议吗？

public FlickrResultSize getPhotos(String link){
    return mMainApiHelper.getPhotos(link);
}