Hi, I'm learning coroutines (coming from Rx world)...

# coroutines

[fal]

Hi, I'm learning coroutines (coming from Rx world) and I'm trying to find a good way to refresh my flows on ViewModel... So far what I've been thinking is creating a shared flow to represent refresh events, something like:

private val refreshFlow =
    MutableSharedFlow<Unit>(replay = 1, onBufferOverflow = BufferOverflow.DROP_OLDEST).apply {
      tryEmit(Unit)
    }

init {
  fetchNews()
}

fun refreshData() {
  refreshFlow.tryEmit(Unit)
}

private fun fetchNews() {
  viewModelScope.launch {
    refreshFlow
        .flatMapLatest { fetchLatestNewsFlow() }
        ...
        .collect()
  }

Is this ok? Are there any better solutions?

[ephemient]

I hope it's ok. we're doing something similar - multiple Flow<Unit> coming from various places, .flattenMerge() them all together for a single stream of "somebody wants a refresh now" triggers

[fal]

@ephemient Do your Flow<Unit>'s somehow represent UI events? Reason I'm asking is because I don't really like having hot flows for this, but I don't see how I could represent UI actions through cold flows

[ephemient]

UI events and server events. how can UI events be cold? it's not like you tell the user to stop pushing buttons

[fal]

Yea, I got confused by your Flow<Unit> explanation (I somehow assumed they were cold), but of course that doesn't actually specify whether they're cold or not 👍 If it's a mix between server and UI events I get it, thanks!

[baxter]

Closest thing I can think of for a RxJava -> Coroutines mappings is:
• If you need to use Single or Maybe, consider using a suspend function or just launch a single use coroutine with launch or async on a scope.
• If you need a stream such as Observable or Flowable, and the stream would complete, use flow {}.
• If the stream is hot, then use MutableSharedFlow() or MutableStateFlow().

[baxter]

I'm guessing here, but it looks like you have a flow coming from fetchLatestNewsFlow() that is doing a single task (fetching the latest news and caching it). You can probably just call fetchLatestNewsFlow().launchIn(viewModelScope) each time you call refreshData().

[baxter]

I would move whatever logic you have in the flow that is run each time you call fetchLatestNewFlow(), unwrap it from the flow block, and make that function a suspend function, so I can just do:

fun refreshData() {
  viewModelScope.launch { fetchLatestNews() }
}

[baxter]

But that's just my 2 🪙

[fal]

@baxter Thanks for the response! I definitely agree with you with your approach, and I don't think the 'fetchLatestNews()' was the best example, since it does imply that a simple suspend function would suffice. My question was a bit more general, in the sense of "what if I want to refresh flows"? Despite this, your tips are definitely helpful and make sense to avoid building flows when they're not necessary 👍