Transforming to presentation model is done on UI thread, because of UseCase limitations

[Doctoror]

In your code, you transform domain entities into presentation model in UI thread, mainly because the UseCase can't access entities from presentation.

E.g. UserDetailsPresenter.java#L100, UserListPresenter.java#L109

Transformations in UI thread is not a really good idea, especially when we have the power of RxJava. So, in my projects, a UseCase is an interface like this

interface UseCase<Params, T> {
    fun buildUseCaseObservable(params: Params): Observable<T>
}

Mainly because I have the following cases. Here, I want to transform some data from repository model into presentation model, but I don't want to do it on UI thread, and I don't want to start another async procedure, or lose convenience of Rx transformation methods, so I apply transformations for the use case observable in my presenter.

disposable = useCase.buildUseCaseObservable(Unit)
                .subscribeOn(schedulers.io())
                .map { SectionedVideoListMapper.transform(it) }
                .observeOn(schedulers.mainThread())
                .subscribe(this::onDataLoaded, this::onDataLoadFailed)

Or here, I cannot pass Intent to domain layer to retrieve the video list, so I do this transformation off UI thread before passing it to UseCase.

Observable.fromCallable { PlaylistVideoMapper.transform(contentResolver, data) }
                .subscribeOn(schedulers.io())
                .flatMap { useCase.buildUseCaseObservable(CreatePlaylistUseCase.Params(name, it)) }
                .observeOn(schedulers.mainThread())
                .subscribe({}, this::onPlaylistCreateFailed)

What do you think about this approach?

[CROSP]

@Doctoror I think it is up to. That's why RxJava is used here as a link between different layers because it makes it much easier to convert, adapt and manipulate data being passed. Furthermore one of the most valuable feature of RxJava is easy threading.

[brianguertin]

I think you are in the right track, the UI thread is a view layer detail and doesn't belong anywhere except in the UI layer, in my opinion.