i'm using this `callbackFlow` to listen updates of...

# coroutines

[Kulwinder Singh]

i'm using this callbackFlow to listen updates of Firestore Collection using below extension function

@ExperimentalCoroutinesApi
fun Query.getQuerySnapshotFlow(): Flow<QuerySnapshot?> = callbackFlow {
    val listenerRegistration = addSnapshotListener { querySnapshot, e ->
        if (e != null) {
            cancel(message = "", cause = e)
            return@addSnapshotListener
        }
        offer(querySnapshot)
    }
    awaitClose {
        listenerRegistration.remove()
    }
}

@ExperimentalCoroutinesApi
fun <T> Query.getDataFlow(mapper: (QuerySnapshot?) -> T): Flow<T> {
    return getQuerySnapshotFlow().map { mapper(it) }
}

and i'm using above extension functions like below inside my ViewModel, but how can i cancel previous Flow, which is started in else case below, because when switchMap is called again then it will keep listening old Collection and will start new one. how can i fix this?

val myAppointments = _appointmentDate.switchMap { date ->
	//HERE I WANT TO CANCEL PREVIOUS FLOW STARTED IN ELSE CASE BELOW
	liveData {
		if (date == null)
			emit(AppointmentState.NoAppointment)
		else {
			myCollection.whereEqualTo(Appointment.DATE, date)
					.getDataFlow { it!!.toObjects<List<Appointment>>() }
					.collect { emit(AppointmentState.Loaded(it)) }
		}
	}
}

[Manuel Vivo]

Easiest way I can think of is by passing a Job to the liveData builder and cancel it when needed

[Kulwinder Singh]

@Manuel Vivo so something like this would be ok ?

val appointmentJob = Job()
val myAppointments = _appointmentDate.switchMap { 
    appointmentJob.complete()
    liveData(appointmentJob) { /.../ }
}

[Kulwinder Singh]

or do i have to add + <http://Dispatcher.IO|Dispatcher.IO> or other with Job?

[Manuel Vivo]

liveData uses Dispatchers.Main

var appointmentJob: Job?
val myAppointments = _appointmentDate.switchMap { date ->
    appointmentJob.cancelIfActive()
    appointmentJob = Job()
    liveData(appointmentJob) { /.../ }
    ...
}

fun Job?.cancelIfActive() {
    if (this?.isActive == true) {
        cancel()
    }
}

[Manuel Vivo]

if you cancel a Job, you cannot use it anymore. That's why you need a fresh instance before calling liveData

[Kulwinder Singh]

thanks @Manuel Vivo it worked 👍

[Manuel Vivo]

Great! My pleasure