RxJava - wait for async task and then call Api

Question

Trying to get lastLocation and once it's done call api. But somehow once location is obtained my api calls always running in mainThread, so i'm getting exception:

android.io.NetworkOnMainThreadException

Here is my location observer:

fun getLocation(): Single<Location> {
        return Single.create<Location> { subscriber ->
            fusedLocationClient.lastLocation.addOnSuccessListener {
                if (it != null) {
                    subscriber.onSuccess(it)
                } else {
                    subscriber.onError(Exception("No location"))
                }
            }
        }
    }

Code that does some transformations

val locationObserver = getLocation()
observables.add(locationObserver.flatMap { _ -> sendDataToServer(data)})

Observer

Single.zip(observables) { args1 -> args1 }.subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread()).subscribe({
            Timber.i("Success")

        }, {
            Timber.i("Error %s", observables.size, it.localizedMessage)
            it.printStackTrace()
        })

I've set subscribeOn so it shouldn't be on mainThread, but looks like something missed.

Found that if i will use something like Single.just("One").flatMap{ ... } that will work fine and will be executed on non-main thread.

Is there something to do with getLocation function?

Jack · Accepted Answer · 2019-03-26 10:18:54Z

1

The order of subscribeOn, observeOn, subscribe, and transformations matters. Apparently, it's needed to do the transformations, in this case, the flatMap after specifying the observer thread with observeOn to make sure the code is executed in the right thread.

edited Mar 26, 2019 at 10:18

answered Mar 25, 2019 at 22:23

Jack

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4 Comments

Андрей Гузюк Over a year ago

After subscribe block it’s no longer observable, so you can’t do that. It’s applicable only before subscribe call

Jack Over a year ago

Oh my bad, what if you switch the order of subscribeOn and observeOn? I used to have a similar problem and changing these orders is what solved it.

Андрей Гузюк Over a year ago

Oh damn, you pointed me in right direction. Please modify your answer to use observeOn(Schedulers.io()) before .flatMap{}

Jack Over a year ago

Glad I did, I have edited the answer, make sure that's what you meant.

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