How do I make a state flow that: - emits its value...

# coroutines

[ribesg]

How do I make a state flow that:
• emits its value immediately every time it changes
• emits its value periodically X seconds after it changes (and keeps doing it until it changes)
• don’t emit anything when the value is null (if it’s changed to null and periodically)

I know how to make a flow that basically combines the origin state flow with an independent periodic flow re-emitting the value of the state flow, but it’s not exactly what I want. I found no simple way to make a timer either

[Joffrey]

I'm curious, could you please explain your use case for re-emitting the same value over and over?

[Michal Klimczak]

sth like?

val trigger = MutableSharedFlow<Sth>()
val flow = trigger.
.flatMapLatest {
   if(it!=null)
   while(true){
      emit(it)
      delay(1000)
   }
   }
}

[Michal Klimczak]

writing from memory, I might be completely wrong

[ephemient]

close. flatMap needs another Flow, you probably meant that wrapped in a flow builder or

trigger.transformLatest { item ->
    emit(item)
    if (item != null) {
        delay(Duration.seconds(1))
        emit(item)
    }
}

the mention of "state flow" is confusing, though. a state flow conflates equals values; if you want something that re-emits the same value, it can't be a StateFlow.

[Joffrey]

+1 for "state flow" and identical value emissions.. I don't get it either, hence my question about the use case here

[Michal Klimczak]

Yeah, both points are valid :)

[Michal Klimczak]

As for the use case - can't speak for op, but I implemented something a bit similar (although in rxjava) for a heartbeat animation which was based on actual user's heartbeat rate.

[andylamax]

Seems like the bullet points listed are jobs for flows and not necessarily state flow

[louiscad]

You most likely want a custom operator for regular `Flow`s or `SharedFlow`s that emits periodically over and over. It could use transformLatest.

[ribesg]

The state flow was basically the primary source of data, not the output of what I wanted. I needed something like that because that data was then converted and mixed with some other data that may or may have not changed (like, the current time) to produce a result, hence why I wanted to re-emit the same thing at the beginning of the flow, resulting in potential actual change later

[ribesg]

I did something less clever in the end. It’ll probably trigger more requests and updates than necessary but it’s not really worth to look for a better option