It’s never easy to write async code but luckily there are many libraries to manage asynchronicity without adding too much complexity. In the last years RxJava and the other ReactiveX libraries have been very popular but lately there is a new way to manage async code in Kotlin: the coroutines. In this talk we’ll see pros and cons of there two approaches and how to leverage them to simplify asynchronous code on Android. Do they solve the same problem? Can we use them together? How can we use them effectively in Android development? Spoiler alert: They are both great!

1. Async code on Kotlin:
RxJava or/and coroutines
Fabio Collini
Milan | November 29 - 30, 2018

2. @fabioCollini
linkedin.com/in/fabiocollini
github.com/fabioCollini
medium.com/@fabioCollini
codingjam.it
Android programmazione
avanzata
Android Developers Italia
Ego slide

6. Single
Maybe
Completable
Observable
Flowable
Cold Vs Hot
Subjects
suspend methods
Job/Deferred
Channels
Actors
Producers
Publishers
BroadcastChannels
RxJava Coroutines

7. Single
Maybe
Completable
Observable
Flowable
Cold Vs Hot
Subjects
suspend methods
Job/Deferred
Channels
Actors
Producers
Publishers
BroadcastChannels
RxJava Coroutines

8. RxJava
Coroutines
OR

9. RxJava
Coroutines
AND

10. CompletableSource.await, MaybeSource.await, MaybeSource.awaitOrDefault,
MaybeSource.openSubscription, SingleSource.await,
ObservableSource.awaitFirst, ObservableSource.awaitFirstOrDefault,
ObservableSource.awaitFirstOrElse, ObservableSource.awaitFirstOrNull,
ObservableSource.awaitLast, ObservableSource.awaitSingle,
ObservableSource.openSubscription, ObservableSource.iterator
RxJava Coroutines->RxJava Coroutines->

11. RxJava Coroutines->
RxJavaCoroutines->
rxCompletable, rxMaybe, rxSingle, rxObservable, rxFlowable
CompletableSource.await, MaybeSource.await, MaybeSource.awaitOrDefault,
MaybeSource.openSubscription, SingleSource.await,
ObservableSource.awaitFirst, ObservableSource.awaitFirstOrDefault,
ObservableSource.awaitFirstOrElse, ObservableSource.awaitFirstOrNull,
ObservableSource.awaitLast, ObservableSource.awaitSingle,
ObservableSource.openSubscription, ObservableSource.iterator
github.com/Kotlin/kotlinx.coroutines/tree/master/reactive/kotlinx-coroutines-rx2

12. github.com/fabioCollini/
RxJavaVsCoroutines

13. interface StackOverflowService {
@GET("/users")
fun getTopUsers(): Single<List<User>>
@GET("/users/{userId}/badges")
fun getBadges(
@Path("userId") userId: Int
): Single<List<Badge>>
@GET("/users/{userId}/top-tags")
fun getTags(
@Path("userId") userId: Int
): Single<List<Tag>>
}0
RxJava

14. interface StackOverflowService {
@GET("/users")
fun getTopUsers(): Single<List<User>>
@GET("/users/{userId}/badges")
fun getBadges(
@Path("userId") userId: Int
): Single<List<Badge>>
@GET("/users/{userId}/top-tags")
fun getTags(
@Path("userId") userId: Int
): Single<List<Tag>>
}0
interface StackOverflowService {
@GET("/users")suspend
fun getTopUsers(): Deferred<List<User>>
@GET("/users/{userId}/badges")suspend
fun getBadges(
@Path("userId") userId: Int
): Deferred<List<Badge>>
@GET("/users/{userId}/top-tags")suspend
fun getTags(
@Path("userId") userId: Int
): Deferred<List<Tag>>
}1
RxJava Coroutines

15. interface StackOverflowService {
@GET("/users")
fun getTopUsers(): Single<List<User>>
@GET("/users/{userId}/badges")
fun getBadges(
@Path("userId") userId: Int
): Single<List<Badge>>
@GET("/users/{userId}/top-tags")
fun getTags(
@Path("userId") userId: Int
): Single<List<Tag>>
}0
interface StackOverflowService {
@GET("/users")suspend
fun getTopUsers(): Deferred<List<User>>
@GET("/users/{userId}/badges")suspend
fun getBadges(
@Path("userId") userId: Int
): Deferred<List<Badge>>
@GET("/users/{userId}/top-tags")suspend
fun getTags(
@Path("userId") userId: Int
): Deferred<List<Tag>>
}1
RxJava Coroutines

16. interface StackOverflowService {
@GET("/users")
fun getTopUsers(): Single<List<User>>
@GET("/users/{userId}/badges")
fun getBadges(
@Path("userId") userId: Int
): Single<List<Badge>>
@GET("/users/{userId}/top-tags")
fun getTags(
@Path("userId") userId: Int
): Single<List<Tag>>
}0
RxJava Coroutines
interface StackOverflowService {
@GET("/users")suspend
fun getTopUsers(): Deferred<List<User>>
@GET("/users/{userId}/badges")suspend
fun getBadges(
@Path("userId") userId: Int
): Deferred<List<Badge>>
@GET("/users/{userId}/top-tags")suspend
fun getTags(
@Path("userId") userId: Int
): Deferred<List<Tag>>
}1

17. interface StackOverflowService {
@GET("/users")
fun getTopUsers(): Single<List<User>>
@GET("/users/{userId}/badges")
fun getBadges(
@Path("userId") userId: Int
): Single<List<Badge>>
@GET("/users/{userId}/top-tags")
fun getTags(
@Path("userId") userId: Int
): Single<List<Tag>>
}0
interface StackOverflowService {
@GET("/users")
suspend fun getTopUsers(): List<User>
@GET("/users/{userId}/badges")
suspend fun getBadges(
@Path("userId") userId: Int
): List<Badge>
@GET("/users/{userId}/top-tags")
suspend fun getTags(
@Path("userId") userId: Int
): List<Tag>
}1
RxJava Coroutines
https://github.com/square/retrofit/pull/2886

18. service.getTopUsers()
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
RxJava

19. service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
RxJava

20. service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
try {
val users = service.getTopUsers()
updateUi(users)
} catch (e: Exception) {
updateUi(e)
}4
RxJava Coroutines

21. try {
val users = service.getTopUsers()
updateUi(users)
} catch (e: Exception) {
updateUi(e)
}4
Coroutines

22. try {
val users = service.getTopUsers()
updateUi(users)
} catch (e: Exception) {
updateUi(e)
}4
Coroutines
suspend fun getTopUsers(): List<User>

23. GlobalScope.launch {
try {
val users = service.getTopUsers()
updateUi(users)
} catch (e: Exception) {
updateUi(e)
}4
}
Coroutines

24. service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
try {
val users = service.getTopUsers()
updateUi(users)
} catch (e: Exception) {
updateUi(e)
}4
RxJava Coroutines

25. class MyViewModel(
private val service: StackOverflowService
) : ViewModel() {
private val disposable = CompositeDisposable()
fun load() {
disposable +=
service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
}A
private fun updateUi(s: Any) {
//...
}B
override fun onCleared() {
disposable.clear()
}C
}D
class MyViewModel(
private val service: StackOverflowService
) : ViewModel() {
fun load() {
viewModelScope.launch {
try {
val users = service.getTopUsers()
updateUi(users)
} catch (e: Exception) {
updateUi(e)
}4
}5
}E
private fun updateUi(s: Any) {
//...
}G
}H
RxJava Coroutines

26. class MyViewModel(
private val service: StackOverflowService
) : ViewModel() {
private val disposable = CompositeDisposable()
fun load() {
disposable +=
service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
}A
private fun updateUi(s: Any) {
//...
}B
override fun onCleared() {
disposable.clear()
}C
}D
class MyViewModel(
private val service: StackOverflowService
) : ViewModel() {
fun load() {
viewModelScope.launch {
try {
val users = service.getTopUsers()
updateUi(users)
} catch (e: Exception) {
updateUi(e)
}4
}5
}E
private fun updateUi(s: Any) {
//...
}G
}H
RxJava Coroutines
viewModelScope

27. viewModelScope
Uses Dispatchers.Main
doesn’t block the Main thread executing a suspending method
Connected to the ViewModel lifecycle
cancels the Jobs when the ViewModel is destroyed
not available yet (but easy to implement)
android-review.googlesource.com/c/platform/frameworks/support/+/772083

28. class MyViewModel(
private val service: StackOverflowService
) : ViewModel() {
private val disposable = CompositeDisposable()
fun load() {
disposable +=
service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
}A
private fun updateUi(s: Any) {
//...
}B
override fun onCleared() {
disposable.clear()
}C
}D
class MyViewModel(
private val service: StackOverflowService
) : ViewModel() {
fun load() {
viewModelScope.launch {
try {
val users = service.getTopUsers()
updateUi(users)
} catch (e: Exception) {
updateUi(e)
}4
}5
}E
private fun updateUi(s: Any) {
//...
}G
}H
RxJava Coroutines

29. service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
val users = service.getTopUsers()
updateUi(users)
} catch (e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

30. service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
val users = service.getTopUsers()
updateUi(users)
} catch (e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

31. service.getTopUsers()
.map_{_it.first()_}_
.flatMap_{_firstUser_->_
service.getBadges(firstUser.id)
}0
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{_badges_->_updateUi(badges)_},
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
val users = service.getTopUsers()
val firstUser = users.first()
val badges = service.getBadges(firstUser.id)
updateUi(badges)
} catch (e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

32. updateUi("loading users")
service.getTopUsers()
.observeOn(mainThread())
.doOnSuccess { updateUi("loading badges") }
.observeOn(io())
.map_{_it.first()_}_
.flatMap_{_firstUser_->_
service.getBadges(firstUser.id)
}0
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{_badges_->_updateUi(badges)_},
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
updateUi("loading users")
val users = service.getTopUsers()
updateUi("loading badges")
val firstUser = users.first()
val badges = service.getBadges(firstUser.id)
updateUi(badges)
} catch (e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

33. service.getTopUsers()
.map_{_it.first()_}_
.flatMap_{_firstUser_->_
service.getBadges(firstUser.id)
}0
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{_badges_->_updateUi(badges)_},
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
val users = service.getTopUsers()
val firstUser = users.first()
val badges = service.getBadges(firstUser.id)
updateUi(badges)
} catch (e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

34. service.getTopUsers()
.map_{_it.first()_}_
.flatMap_{_firstUser_->_
service.getBadges(firstUser.id)
}0
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{_badges_->_updateUi(badges)_},
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
val badges = withContext(IO) {
val users = service.getTopUsers()
val firstUser = users.first()
service.getBadges(firstUser.id)
}3
updateUi(badges)
} catch (e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

35. RxJava Coroutines
Schedulers
subscribeOn defines
when the computation
starts
observeOn changes the
thread (until next
observeOn)
Dispatchers
the computation starts on
the context dispatcher
withContext changes the
thread in a block

36. service.getTopUsers()
.map_{_it.first()_}_
.flatMap_{_firstUser_->_
service.getBadges(firstUser.id)
}0
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{_badges_->_updateUi(badges)_},
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
val badges = withContext(IO) {
val users = service.getTopUsers()
val firstUser = users.first()
service.getBadges(firstUser.id)
}3
updateUi(badges)
} catch (e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

37. service.getTopUsers()
.map_{_it.first()_}_
.flatMap_{_firstUser_->_
service.getBadges(firstUser.id)
.map { badges ->
UserStats(firstUser, badges)
}p
}0
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{_userWithBadges_->_
updateUi(userWithBadges)
},
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
val userWithBadges = withContext(IO) {
val users = service.getTopUsers()
val firstUser = users.first()
val badges = service.getBadges(
firstUser.id)
UserStats(firstUser, badges)
}3
updateUi(userWithBadges)
} catch (e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

38. RxJava
service.getTopUsers()
.map_{_it.first()_}_
.flatMap_{_user_->_
service.getBadges(user.id)
.map { badges ->
UserStats(user, badges)
}p
}0

39. service.getTopUsers()
.flattenAsObservable { it.take(5) }
.concatMapEager { user ->
service.getBadges(user.id)
.map { badges ->
UserStats(user, badges)
}p
.toObservable()
}0
.toList()
RxJava

40. Coroutines
viewModelScope.launch {
try {
val userWithBadges = withContext(IO) {
val users = service.getTopUsers()
val firstUser = users.first()
val badges = service.getBadges(
firstUser.id)
UserStats(firstUser, badges)
}3
updateUi(userWithBadges)
} catch (e: Exception) {
updateUi(e)
}4
}5

41. viewModelScope.launch {
try {
val usersWithBadges = withContext(IO) {
service.getTopUsers()
.take(5)
.map { user ->
UserStats(user,
service.getBadges(user.id))
}2
}3
updateUi(usersWithBadges)1
} catch (e: Exception) {
updateUi(e)
}4
}5
Coroutines

42. service.getTopUsers()
.flattenAsObservable { it.take(5) }
.concatMapEager { user ->
service.getBadges(user.id)
.map { badges ->
UserStats(user, badges)
}p
.toObservable()
}0
.toList()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ usersWithBadges ->
updateUi(usersWithBadges)
},
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
val usersWithBadges = withContext(IO) {
service.getTopUsers()
.take(5)
.map { user ->
UserStats(user,
service.getBadges(user.id))
}2
}3
updateUi(usersWithBadges)1
} catch (e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

43. service.getTopUsers()
.flattenAsObservable { it.take(5) }
.concatMapEager { user ->
service.getBadges(user.id)
.map { badges ->
UserStats(user, badges)
}p
.subscribeOn(io())
.toObservable()
}0
.toList()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ usersWithBadges ->
updateUi(usersWithBadges)
},
{ e -> updateUi(e) }
)1
RxJava Coroutines
viewModelScope.launch {
try {
val usersWithBadges = withContext(IO) {
service.getTopUsers()
.take(5)
.map { user ->
UserStats(user,
service.getBadges(user.id))
}2
}3
updateUi(usersWithBadges)1
} catch (e: Exception) {
updateUi(e)
}4
}5

44. service.getTopUsers()
.flattenAsObservable { it.take(5) }
.concatMapEager { user ->
service.getBadges(user.id)
.map { badges ->
UserStats(user, badges)
}p
.subscribeOn(io())
.toObservable()
}0
.toList()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ usersWithBadges ->
updateUi(usersWithBadges)
},
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
val usersWithBadges = withContext(IO) {
service.getTopUsers()
.take(5)
.map { user ->
async {
UserStats(user,
service.getBadges(user.id))
}
}2
.map { it.await() }
}3
updateUi(usersWithBadges)1
} catch (e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

45. service.getTopUsers()
.flattenAsObservable { it.take(5) }
.concatMapEager { user ->
userDetail(user)
.subscribeOn(io())
.toObservable()
}0
.toList()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ users ->
updateUi(users)
},
{ e -> updateUi(e) }
)1
fun userDetail(user: User): Single<UserStats> {
return service.getBadges(user.id)
.map { badges ->
UserStats(user, badges)
}7
}8
RxJava Coroutines
viewModelScope.launch {
try {
val usersWithBadges = withContext(IO) {
service.getTopUsers()
.take(5)
.map { user ->
async {
UserStats(user,
service.getBadges(user.id))
}
}2
.map { it.await() }
}3
updateUi(usersWithBadges)1
} catch (e: Exception) {
updateUi(e)
}4
}5

46. service.getTopUsers()
.flattenAsObservable { it.take(5) }
.concatMapEager { user ->
userDetail(user)
.subscribeOn(io())
.toObservable()
}0
.toList()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ users ->
updateUi(users)
},
{ e -> updateUi(e) }
)1
fun userDetail(user: User): Single<UserStats> {
return service.getBadges(user.id)
.map { badges ->
UserStats(user, badges)
}7
}8
viewModelScope.launch {
try {
val usersWithBadges = withContext(IO) {
service.getTopUsers()
.take(5)
.map { user ->
async {
userDetail(user)
}
}2
.map { it.await() }
}3
updateUi(usersWithBadges)1
} catch (e: Exception) {
updateUi(e)
}4
}5
suspend fun userDetail(user: User): UserStats {
return UserStats(user,
service.getBadges(user.id))
}9
RxJava Coroutines

47. fun userDetail(user: User): Single<UserStats> {
return service.getBadges(user.id)
.map { badges ->
UserStats(user, badges)
}7
}8
suspend fun userDetail(user: User): UserStats {
return UserStats(user,
service.getBadges(user.id))
}9
RxJava Coroutines

48. suspend fun userDetail(user: User): UserStats {
return UserStats(user,
service.getBadges(user.id))
}9
RxJava Coroutines
fun userDetail(user: User): Single<UserStats> {
return Singles.zip(
service.getBadges(user.id).subscribeOn(io()),
service.getTags(user.id).subscribeOn(io())) {
badges, tags -> UserStats(user, badges, tags)
}7
}8

49. suspend fun userDetail(user: User): UserStats {
return UserStats(user,
service.getBadges(user.id))
}9
Coroutines

50. suspend fun userDetail(user: User): UserStats {
val badges = service.getBadges(user.id)
val tags = service.getTags(user.id)
return UserStats(user, badges, tags)
}9
Coroutines

51. suspend fun userDetail(user: User): UserStats {
val badges = async { service.getBadges(user.id) }
val tags = async { service.getTags(user.id) }
return UserStats(user, badges.await(), tags.await())7
}9
Coroutines

52. suspend fun userDetail(user: User): UserStats {
return coroutineScope {
val badges = async { service.getBadges(user.id) }
val tags = async { service.getTags(user.id) }
UserStats(user, badges.await(), tags.await())7
}8
}9
Coroutines

53. suspend fun userDetail(user: User): UserStats {
return coroutineScope {
val badges = async { service.getBadges(user.id) }
val tags = service.getTags(user.id)
UserStats(user, badges.await(), tags)7
}8
}9
Coroutines

54. service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
val users = service.getTopUsers()
updateUi(users)
} catch (e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

55. service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.timeout(10, SECONDS)
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
RxJava Coroutines
viewModelScope.launch {
try {
val users = service.getTopUsers()
updateUi(users)
} catch (e: Exception) {
updateUi(e)
}4
}5

56. service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.timeout(10, SECONDS)
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
withTimeout(SECONDS.toMillis(10)) {
val users = service.getTopUsers().await()
updateUi(users)
}6
} catch (e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

57. service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.timeout(10, SECONDS)
.retry(3)
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
retry(3) {
withTimeout(SECONDS.toMillis(10)) {
val users = service.getTopUsers().await()
updateUi(users)
}6
}7
} catch_(e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

58. service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.timeout(10, SECONDS)
.retry(3)
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
retry(3) {
withTimeout(SECONDS.toMillis(10)) {
val users = service.getTopUsers().await()
updateUi(users)
}6
}7
} catch_(e: Exception) {
updateUi(e)
}4
}5
suspend fun <T> retry(attempts: Int,
f: suspend () -> T): T {
repeat(attempts - 1) {
try {
return f()
} catch (e: Exception) {
}
}
return f()
}
RxJava Coroutines

59. service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.timeout(10, SECONDS)
.retry(3)
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
retry(3) {
withTimeout(SECONDS.toMillis(10)) {
val users = service.getTopUsers().await()
updateUi(users)
}6
}7
} catch_(e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

60. service.getTopUsers()
.subscribeOn(io())
.observeOn(mainThread())
.timeout(10, SECONDS)
.retryWhen(ExponentialBackoff(3))
.subscribe(
{ users -> updateUi(users) },
{ e -> updateUi(e) }
)1
viewModelScope.launch {
try {
exponentialBackoff(3) {
withTimeout(SECONDS.toMillis(10)) {
val users = service.getTopUsers().await()
updateUi(users)
}6
}7
} catch_(e: Exception) {
updateUi(e)
}4
}5
RxJava Coroutines

61. Wrapper of a synchronous method
fun myPref(): String =
prefs.getString("myPref", "")
fun myPref(): Single<String> =
Single.fromCallable {
prefs.getString("myPref", "")
}1
suspend fun myPref(): String =
withContext(IO) {
prefs.getString("myPref", "")
}2
RxJavaCoroutines

62. Wrapper of an asynchronous method
fun View.scale(v: Float): ViewPropertyAnimator {
return animate()
.scaleX(v)
.scaleY(v)
}4

63. Wrapper of an asynchronous method
fun View.scale(v: Float): ViewPropertyAnimator {
return animate()
.scaleX(v)
.scaleY(v)
}4
text.setOnClickListener {
text.scale(2f).withEndAction {
text.scale(1f)
}1
}2

64. Wrapper of an asynchronous method
fun View.scale(v: Float): ViewPropertyAnimator {
return animate()
.scaleX(v)
.scaleY(v)
}4
text.setOnClickListener {
text.scale(2f).withEndAction {
text.scale(1f).withEndAction {
text.scale(2f).withEndAction {
text.scale(1f)
}3
}4
}1
}2

65. Wrapper of an asynchronous method
fun View.scale(value: Float): Completable =
Completable.create { emitter ->
val animator = animate()
animator.scaleX(value).scaleY(value).withEndAction {
emitter.onComplete()
}3
}4
text.setOnClickListener {
text.scale(2f).withEndAction {
text.scale(1f).withEndAction {
text.scale(2f).withEndAction {
text.scale(1f)
}3
}4
}1
}2
RxJava

66. Wrapper of an asynchronous method
fun View.scale(value: Float): Completable =
Completable.create { emitter ->
val animator = animate()
animator.scaleX(value).scaleY(value).withEndAction {
emitter.onComplete()
}3
}4
text.setOnClickListener {
text.scale(2f)
.andThen(text.scale(1f))
.andThen(text.scale(2f))
.andThen(text.scale(1f))
.subscribe()
}2
RxJava

67. Wrapper of an asynchronous method
suspend fun View.scale(v: Float) =
suspendCoroutine<Unit> { continuation ->
animate()
.scaleX(v)
.scaleY(v)
.withEndAction { continuation.resume(Unit) }
}1
Coroutines

68. Wrapper of an asynchronous method
suspend fun View.scale(v: Float) =
suspendCoroutine<Unit> { continuation ->
animate()
.scaleX(v)
.scaleY(v)
.withEndAction { continuation.resume(Unit) }
}1
text.setOnClickListener {
launch {
text.scale(2f)
text.scale(1f)
text.scale(2f)
text.scale(1f)
}
}
Coroutines

69. Autocomplete

70. A
0
100
200
300
400
500
600
700
800
900
1000
L
Server
AL
AL -> Alabama, Alaska, California

71. A0
100
200
300
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500
600
700
800
900
1000
L
Server
AL
AL -> Alabama, Alaska, California
A
ALA
ALA -> Alabama, Alaska

72. RxTextView.textChanges(auto_complete)
RxJava

73. RxTextView.textChanges(auto_complete)
.debounce(200, MILLISECONDS)
RxJava

74. RxTextView.textChanges(auto_complete)
.debounce(200, MILLISECONDS)
.switchMapSingle {
retrieveData(it.toString()).subscribeOn(io())
}
RxJava

75. RxTextView.textChanges(auto_complete)
.debounce(200, MILLISECONDS)
.switchMapSingle {
retrieveData(it.toString()).subscribeOn(io())
}
.subscribeOn(io())
.observeOn(mainThread())
RxJava

76. RxTextView.textChanges(auto_complete)
.debounce(200, MILLISECONDS)
.switchMapSingle {
retrieveData(it.toString()).subscribeOn(io())
}
.subscribeOn(io())
.observeOn(mainThread())
.subscribe {
adapter.clear()
adapter.addAll(it)
}
RxJava

77. val channel: SendChannel<String> = actor(capacity = CONFLATED) {
consumeEach { s ->
launch {
val data = retrieveData(s)
adapter.clear()
adapter.addAll(data)
}5
}5
}5
autoComplete.doOnTextChanged {
channel.offer(it)
}6
Coroutines

78. val channel: SendChannel<String> = actor(capacity = CONFLATED) {
consumeEach { s ->
launch {
val data = retrieveData(s)
adapter.clear()
adapter.addAll(data)
}5
}5
}5
autoComplete.doOnTextChanged {
channel.offer(it)
}6
Coroutines

79. val channel: SendChannel<String> = actor(capacity = CONFLATED) {
consumeEach { s ->
launch {
val data = retrieveData(s)
adapter.clear()
adapter.addAll(data)
}5
}5
}5
autoComplete.doOnTextChanged {
channel.offer(it)
}6
Coroutines

80. val channel: SendChannel<String> = actor(capacity = CONFLATED) {
consumeEach { s ->
launch {
val data = retrieveData(s)
adapter.clear()
adapter.addAll(data)
}5
}5
}5
autoComplete.doOnTextChanged {
channel.offer(it)
}6
Coroutines

81. val channel: SendChannel<String> = actor(capacity = CONFLATED) {
consumeEach { s ->
launch {
val data = retrieveData(s)
adapter.clear()
adapter.addAll(data)
}5
}5
}5
autoComplete.doOnTextChanged {
channel.offer(it)
}6
Coroutines

82. val channel: SendChannel<String> = actor(capacity = CONFLATED) {
var lastJob: Job? = null
consumeEach { s ->
lastJob?.cancel()
lastJob = launch {
delay(200)
val data = retrieveData(s)
adapter.clear()
adapter.addAll(data)
}5
}5
}5
autoComplete.doOnTextChanged {
channel.offer(it)
}6
Coroutines

83. Debugging
RxJava Coroutines

84. 11051 io.reactivex
144 kotlin.coroutines
1984 kotlinx.coroutines
Method count - debug

85. 427 io.reactivex
77 kotlin.coroutines
493 kotlinx.coroutines
Method count - release

86. RxJava and coroutines are both great,
which one should I use?

87. My algorithm:
If you are already using RxJava and it works for you ->
RxJava
If the architecture is based on reactive stream -> RxJava
If the project is multiplatform with Kotlin Native ->
Coroutines
If the codebase is Java/Kotlin -> RxJava
else -> Coroutines
RxJava and coroutines are both great,
which one should I use?

88. Links
Demo Project
github.com/fabioCollini/RxJavaVsCoroutines
Guide to kotlinx.coroutines by example
github.com/Kotlin/kotlinx.coroutines/blob/master/coroutines-guide.md
Kotlin coroutines, a deeper look
medium.com/@elizarov/kotlin-coroutines-a-deeper-look-180536305c3f
Async code using Kotlin Coroutines
proandroiddev.com/async-code-using-kotlin-coroutines-233d201099ff
ViewModelScope
android-review.googlesource.com/c/platform/frameworks/support/+/772083
Retrofit suspending methods support
github.com/square/retrofit/pull/2886

89. THANKS
FOR YOUR
ATTENTION

90. QUESTIONS?
Android Developers Italia
androiddevs.it