If I want to make a server request but also at the same time kotlinlang #coroutines

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.

i.e.

Copy code

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]

02/28/2021, 1:36 AM

Are you saying that code snippet looks messy to you?

Also that should be

launch

not

async

spierce7

02/28/2021, 2:03 AM

oops, yeah, I was playing around with it

I guess that does exactly what I want it too.

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

Copy code

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

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

launch

Zach Klippenstein (he/him) [MOD]

02/28/2021, 2:30 AM

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

spierce7

02/28/2021, 2:46 AM

I thought launch would have transferred it to the ExceptionHandler.

it only would propagate I thought if I did

async / await

Zach Klippenstein (he/him) [MOD]

02/28/2021, 3:06 AM

if you use

async

without

await

it will actually not propagate at all, just drop.

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

Albert Chang

02/28/2021, 3:49 AM

You can use

flow

builder and

stateIn

like the example shown here.

spierce7

02/28/2021, 4:00 AM

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.

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