2019/1/23に開催されたLINE Developer Meetup #49 in Kyotoでの登壇資料です

1. Reduce dependency
on Rx
with Kotlin
Coroutines
LINE Fukuoka
@umakoz
2019 1 23 LINE Developer Meetup #49 in KYOTO

2. About me
• LINE Fukuoka 3
•
• @umakoz
• LINE Creators Studio for Android
•
!
3°02'03"

3. LINE Creators Studio
• LINE
•
•
https://creator.line.me/ja/studio/

4. inside LINE Creators Studio
• Pure Kotlin without Library
• MVVM
• RxJava2, RxKotlin, RxLifecycle, Retrofit2, Realm...

5. Rx
ReactiveX
Reactive Extensions
An API for
asynchronous programming
with observable streams.

6. Rx
• Create
Easily create event streams or data streams.
• Combine
Compose and transform streams with query-like operators.
• Listen
Subscribe to any observable stream to perform side effects.

7. Rx

8. RxJava
A Java VM implementation of
Reactive Extensions

9. RxJava event/data stream
• Observable
0..N flows, no backpressure,
• Flowable
0..N flows, supporting Reactive-Streams and backpressure

10. RxJava event/data stream
• Single
a flow of exactly 1 item or an error,
• Completable
a flow without items but only a completion or error signal,
• Maybe
a flow with no items, exactly one item or an error.

11. async code using RxJava2
fun loadSticker(id: Int): Single<Sticker> = ...
loadSticker(id)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(
{ sticker -> show(sticker) },
{ error -> showError(error) }
)

12. difficulty of Rx
•
• Functional Programming
• Reactive Programming
• operator
http://reactivex.io/documentation/operators.html
• Hot / Cold
•

13. Kotlin 1.3 Released
Coroutines

14. Coroutines
: co-routine
co
https://ja.wikipedia.org/wiki/

15. async code using Coroutines
suspend fun loadSticker(id: Int): Sticker = ...
GlobalScope.launch(Dispatchers.Main) {
try {
val sticker = async(Dispatchers.IO) {
loadSticker(id)
}.await()
show(sticker)
} catch (error: Exception) {
showError(error)
}
}

16. Coroutine scope
A fundamental building block of coroutines.
• threading
• life-cycle
object GlobalScope : CoroutineScope

17. Coroutine builder
Starts coroutine from a regular non-suspending scope.
fun CoroutineScope.launch(
context: CoroutineContext = EmptyCoroutineContext,
start: CoroutineStart = CoroutineStart.DEFAULT,
block: suspend CoroutineScope.() -> Unit
): Job
fun <T> CoroutineScope.async(
context: CoroutineContext = EmptyCoroutineContext,
start: CoroutineStart = CoroutineStart.DEFAULT,
block: suspend CoroutineScope.() -> T
): Deferred<T>

18. Coroutine dispatcher
Ensures that the execution of a coroutine gets dispatched on
the right thread.
• Dispatchers.Main
• Dispatchers.Default
• Dispatchers.IO
• Dispatchers.Unconfined

19. suspend function
Suspends execution of the code without blocking the current
thread of execution.
suspend fun loadSticker(id: Int): Sticker = ...

20. async code using Coroutines
suspend fun loadSticker(id: Int): Sticker = ...
GlobalScope.launch(Dispatchers.Main) {
try {
val sticker = async(Dispatchers.IO) {
loadSticker(id)
}.await()
show(sticker)
} catch (error: Exception) {
showError(error)
}
}

21. Compare RxJava2 stream with
Coroutines
RxJava2 Coroutines
Observable ReceiveChannel (experimental)
Flowable ReceiveChannel (experimental)
Single Deferred
Completable Job
Maybe Deferred

22. kotlinx-coroutines-rx2
• Modules that provide builders and iteration support for
various reactive streams libraries:
• Reactive Streams, RxJava 2.x, and Project Reactor
https://github.com/Kotlin/kotlinx.coroutines/blob/master/
reactive/kotlinx-coroutines-rx2

23. RxJava2 to Coroutines
suspend fun <T> SingleSource<T>.await(): T
suspend fun CompletableSource.await(): Unit
suspend fun <T> MaybeSource<T>.await(): T?

24. Coroutines to RxJava2
fun CoroutineScope.rxSingle(...): Single
fun CoroutineScope.rxCompletable(...): Completable
fun CoroutineScope.rxMaybe(...): Maybe

25. How to use Coroutines on MVVM

26. retrofit2-kotlin-coroutines-adapter
A Retrofit 2 CallAdapter.Factory for RxJava2's Single.
interface MyService {
@GET("/sticker")
fun loadSticker(id: Int): Single<Sticker>
}

27. retrofit2-kotlin-coroutines-adapter
A Retrofit 2 CallAdapter.Factory for Kotlin coroutine's Deferred.
interface MyService {
@GET("/sticker")
fun loadSticker(id: Int): Deferred<Sticker>
}
https://github.com/JakeWharton/retrofit2-kotlin-coroutines-
adapter

28. Conclusion
• Coroutines
• RxJava2 Coroutines
• Coroutine Channel experimental
• API DB Coroutines
• View Rx Observable operator

29. Thank you