Im trying to switch between flows depending on another flow :slightly_smiling_face: ``` val r...

# flow

[Mikael Alfredsson]

Im trying to switch between flows depending on another flow 🙂

val result = state.transformLatest {
            when (it) {
                "a" -> emitAll(emitter("A"))
                "c" -> emitAll(emitter("C"))
            }
        }

        result.collect {
            println(it)
        }

this will print a flow of A+<counter> or “C” +<counter> depending on the last value from “state”.

I would like to ignore “unknown” states, but since transformLatest cancels the previous flow even if i don’t emit anything new, setting the state to “B” will just cancel the output, not continue on the previous selected output. Is there a nice way to achieve what I want?

[wasyl]

you could filter the unknown states before transformLatest?

[Mikael Alfredsson]

Yes, its possible, but then I’ll have 2 places to update and keep in sync when new values should be “known”

[Mikael Alfredsson]

state.filter{it=="a" || it=="c"}.transformLatest

[Mikael Alfredsson]

it feels a bit redundant 🙂 I would like to have a transformLatest that only cancels the old job if I emit a new flow, not on all new incoming values.

[wasyl]

I don’t think there’s an API for that, other than being able to implement your own operator (which in case of transform isn’t that straightforward I think). I’d probably just go for some pattern like Map<String, ???> so that I have single source of truth for filter { handlers.contains(it) } and for the transform

[Mikael Alfredsson]

great minds and all that 🙂
I ended up fixing it with a mapOf<State, Flow<String>> and filter

[darkmoon_uk]

How about:

myFlow
   .filter { it.isNotUnknown() }
   .distinctUntilChanged()
   .flatMapLatest {
      // Choose output flow
   }

[bezrukov]

you can just map letter to flow before transform latest:

state.mapNotNull { 
    when (it) {
       "a" -> emitter("a")
       "b" -> emitter("b")
       else -> null
     }
}.flatMapLatest { it }