CODEWITHSUNDEEP
androidkotlinkotlin-coroutineskotlin-flowkotlin-stateflow
Cruces
Cruces

Reputation: 3119

Kotlin Flows, executing code when there are no active subscribers

I have created a location repository that is responsible for collecting location data and transmitting it to whoever listens, the code right now looks something like this:

@Singleton
class LocationRepository @Inject constructor(
    app: Application
) {

    private val _location = MutableStateFlow<Location?>(null)
    private val subscribers = AtomicInteger()
    val location: Flow<Location?> = _location.onSubscription {
        if (subscribers.getAndIncrement() == 0)
            startUpdates()
    }.onCompletion {
        if (subscribers.decrementAndGet() == 0)
            stopUpdates()
    }

    private val client = LocationServices.getFusedLocationProviderClient(app)
    private val locCb = object : LocationCallback() {
        override fun onLocationResult(var1: LocationResult?) {
            newLocationResult(var1)
        }
        override fun onLocationAvailability(var1: LocationAvailability) {}
    }
    private val request = LocationRequest.create()

    init {
        request.priority = LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY
        request.interval = 5000L
        request.fastestInterval = 2500L
    }


    private fun startUpdates() { //code to start getting location updates }
    private fun stopUpdates() { //code to stop getting location updates }

}

right now I am handling the current number of subscribers with an AtomicInteger, is there a way to run the startUpdates code and the stopUpdates code automatically when the first subscriber subscribes and the last subscriber unsubscribes?

Upvotes: 1

Views: 2706

Answers (1)

Sergio
Sergio

Reputation: 30645

Please check subscriptionCount property of MutableSharedFlow, it may be what you are looking for. It has type of StateFlow<Int> and emits the number of subscribers (active collectors) to this shared flow. Example:

_location.subscriptionCount
    .map { count -> count > 0 } // map count into active/inactive flag
    .distinctUntilChanged() // only react to true<->false changes
    .onEach { isActive -> // configure an action
        if (isActive) startUpdates() else stopUpdates()
    }
    .launchIn(scope) // launch it

Upvotes: 5

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