I've got a StateFlow that doesn't seem to emit any values (classic StateFlow problem) I don't think...

# coroutines

[Tim Malseed]

I've got a StateFlow that doesn't seem to emit any values (classic StateFlow problem)

I don't think this is due to object equality, but I can't figure out what's going on..

[Tim Malseed]

val skuDetails: MutableStateFlow<Set<SkuDetails>> = MutableStateFlow(emptySet())

Elsewhere:

val newSet = skuDetails.value.toMutableSet()
    newSet.addAll(skuDetailsResult.skuDetailsList.orEmpty())
    skuDetails.value = newSet

Collecting values:

coroutineScope.launch {
       skuDetails.collect {
            Timber.i("sku details: $it") // Never called
        }
    }

[Tim Malseed]

Any ideas? The CoroutineScope isn't being cancelled. The new set of values != the previous set.

[gildor]

This code should work, I think only debug can help
Maybe some deadlock? Maybe you have some blocking code which blocks dispatcher of you scope

[Tim Malseed]

OK, I think I'm just calling collect too late, and missing the emissions

[Tim Malseed]

Nope. I don't really understand what's going on.

I am calling the 'collecting values' block from a function. If I instead move that to the class init { }, the StateFlow emits as expected

[Tim Malseed]

This works:

init {
    skuDetails.onEach {
        Timber.i("Emitting ${it.size} sku details")
    }.launchIn(coroutineScope)
}

This doesn't:

fun start() {
    skuDetails.onEach {
        Timber.i("Emitting ${it.size} sku details")
    }.launchIn(coroutineScope)
}

foo.start()

[Tim Malseed]

Even though the StateFlow isn't updated until after start() is called.

[Tim Malseed]

I'm sure there's a logical explanation, but I just don't understand what's going on here

[wasyl]

You’d need to give some more context, just changing init to fun start() is trivial but clearly there’s something more tricky going on in your codebase

[louiscad]

Looks like you want a SharedFlow with a replay buffer instead of StateFlow.

[Tim Malseed]

OK, I'll see if I can replicate this in Kotlin playgrounds. Hard for me to provide more context without dumping a lot of code

[Tim Malseed]

@louiscad why's that?

[louiscad]

I don't know, I said "looks like", you know your exact use case better.

[Tim Malseed]

Can you explain why it looks that way to you?

[louiscad]

Because it seems you want to get value updates that happen before collect is called.

[Tim Malseed]

Doesn't StateFlow hold the most recent value though?

[louiscad]

Yes it does, and I'm pretty sure you have it.

[Scott Kruse]

@Tim Malseed are you calling the collect block from a suspend function?