Hello all, I have a question about the best appro...

# rx

[nicka]

Hello all,

I have a question about the best approach to handling conditional/if-else situation. I have an API response that will return one of three classes: Loading, Error, or Finished — all of which inherit from a class called: NetworkState.

If its Loading or Error, I want to update my UI appropriately. If its finished, I need to extract the data, do further transformations, then update the UI. I also need to perform a side-effect depending on one of the values returned.

I can think of two ways to do this. Which of these is preferable? Is there a better third option?

OPTION 1

fetchFromApi().
  .map {
    when (it) {
      is Loading -> transformToLoadingView()
      is Error -> transformToErrorView()
      is Finished -> mapDataToUI(it.data)
  }.subscribe { view -> updateUi(view) }

fun mapDataToUI(data: Data) {
  performSideEffect(data)
  transformDataToView(data)
}

OPTION 2

val sharedResponse = fetchFromApi().share()

Observable.merge(
  sharedResponse.ofType('Loading').map { loadingView },
  sharedResponse.ofType('Error').map { errorView },
  sharedResponse.ofType('Finished').map { transformDataToView(it) }
).subscribe { view -> updateUi(view) }

sharedResponse.ofType('Finished').subscribe { performSideEffect(it) }

[nicka]

option two is nice because the side-effect is isolated into its own subscription.

Also, I’ve heard in Rx you should be trying to avoid branching logic like whens/if-else etc

but what’s preferrable?

[ghedeon]

option 1 is much easier to read, tho, less noisy. Unrelated, but I've never understood why people use loading in result of the api call simple smile. Don't you always know that you're loading when you subsribe?

[nicka]

I agree its easier to read; however what’s more consistent with sortof the “philosophy” of Rx?

(also unfortunately the loading thing is outside of my control — agree its not great)

[edwardwongtl]

The Loading State is just for keeping the whole application state inside the viewModel instead of letting the view to decide if it is loading or not.

[nicka]

@edwardwongtl any thoughts on the above two options?

[nicka]

tagging @ursus too because he seems active here

[ursus]

2 could be dont without the share, with publish that takes a function

[ursus]

if youre gonna do just mapping then 1, but 2 gives you options to add different operators

[ursus]

per branch

[edwardwongtl]

I would say I prefer 1