Quick question, and hopefully a quick answer :slightly_smiling_face: : How does one terminate a `Flo...

# coroutines

[streetsofboston]

Quick question, and hopefully a quick answer 🙂 :
How does one terminate a Flow<T> (successfully or with an error)?
The FlowCollector<T> only has an emit method.

[Dominaezzz]

From which end do you want to terminate from? Sender or receiver?

[streetsofboston]

The sender/producer side.

[Paul Woitaschek]

Throw a CancellationException for cancelling it or throw an exception if you want to throw an exception

[Dominaezzz]

It depends on how you are creating the flow. Are you using the flow { } builder?

[jw]

for successful completion just let the block end

[streetsofboston]

Yep… it seems exiting the flow { ... } lambda, it ends…

[streetsofboston]

Ah… Thanks!

[jw]

for error, throw any exception you like

[streetsofboston]

How would I use a FlowCollector in a callback that repeatedly calls back?

[jw]

you probably want flowViaChannel

[jw]

you can close the channel to complete

[streetsofboston]

Thank you!

[streetsofboston]

Without using Channels, would something like this work?

val gpsCoordsFlow: Flow<Pair<Double, Double>> = flow {
        coroutineScope {
            gpsManager.registerListener { coord ->
                launch { emit(coord) }
        }
        suspendCoroutine<Nothing> { /* nothing */ }
    }

(would need extra code to properly un-register the listener, etc.)

[jw]

the downside of that is it launches one coroutine per callback invocation whereas a channel only creates one coroutine in total

[streetsofboston]

Or share the Flow to avoid multiple registrations: 🙂
https://github.com/Kotlin/kotlinx.coroutines/issues/1086