If I want to make a server request, but also, at the same time subscribe to further updates of that ...

# coroutines

[spierce7]

If I want to make a server request, but also, at the same time subscribe to further updates of that data from a StateFlow (driven separately by something i.e. a push message telling the app the data is fresh), what would the best way to do that? Something to keep in mind is I need to pass exceptions from the server request though as well.

I haven’t found an elegant way to do this without it getting messy.

[spierce7]

i.e.

private val headlinesStateFlow = MutableStateFlow<List<Headline>?>(null)

suspend fun headlines(): Flow<List<Headline>> = flow {
    coroutineScope {
        async {
            headlinesStateFlow.emit(videoService.getHeadlines())
        }

        emitAll(headlinesStateFlow.filterNotNull())
    }
}

[Zach Klippenstein (he/him) [MOD]]

Are you saying that code snippet looks messy to you?

[Zach Klippenstein (he/him) [MOD]]

Also that should be launch not async

[spierce7]

oops, yeah, I was playing around with it

[spierce7]

I guess that does exactly what I want it too.

[spierce7]

actually it doesn’t, but I suppose this does:

suspend fun headlines(): Flow<List<Headline>> = flow {
    coroutineScope {
        headlinesStateFlow.emit(videoService.getHeadlines())
        emitAll(headlinesStateFlow.filterNotNull())
    }
}

[spierce7]

I’m not entirely certain what would have happened to the server errors in the original launch

[Zach Klippenstein (he/him) [MOD]]

they’d have been propagated through your flow due to structured concurrency

[spierce7]

I thought launch would have transferred it to the ExceptionHandler.

[spierce7]

it only would propagate I thought if I did async / await

[Zach Klippenstein (he/him) [MOD]]

if you use async without await it will actually not propagate at all, just drop.

[Zach Klippenstein (he/him) [MOD]]

https://elizarov.medium.com/structured-concurrency-722d765aa952

[Albert Chang]

You can use flow builder and stateIn like the example shown here.

[spierce7]

Hey! this looks promising. The example code in the documentation doesn’t make it obvious how to use it though. A few pieces are missing i think.