Presentation for Android Taipei 20181024 - https://www.facebook.com/groups/AndroidTaipei/?multi_permalinks=1858640637590324&notif_id=1540386391612772&notif_t=group_activity&ref=notif

1. Kotlin Coroutines （入門）
CHOCOTV
Louis & Timmy
Android Taipei 20181024

2. Topics
● Asynchronous
● suspend
● async/await
● Android
○ network
○ lifecycle
○ performance
● QA

3. Asynchronous

5. fun test(userId:String){
val token = getToken(userId)
val userName = getUserName(token)
sendMessage("User id is $userId and name is $userName")
}
fun getToken(userId : String) : String
fun getUserName(token : String) : String
fun sendMessage(message : String) : String

6. fun test(userId:String){
val token = getToken(userId)
val userName = getUserName(token)
sendMessage("User id is $userId and name is $userName")
}
fun getToken(userId : String) : String
fun getUserName(token : String) : String
fun sendMessage(message : String) : String

7. fun test(userId:String){
val token = getToken(userId)
val userName = getUserName(token)
sendMessage("User id is $userId and name is $userName")
}
@WorkThread
fun getToken(userId : String) : String
@WorkThread
fun getUserName(token : String) : String
fun sendMessage(message : String) : String

8. fun test(userId:String, callback:()->Unit){
getToken(userId) token-> {
getUserName(token) userName->{
sendMessage("User id is $userId and name is $userName"){
callback.invoke()
}
}
}
}
fun getToken(userId : String , callback:(String)->Unit)
fun getUserName(token : String , callback:(String)->Unit)
fun sendMessage(message : String , callback:(String)->Unit)

9. fun test(userId:String, callback:()->Unit){
getToken(userId) token-> {
getUserName(token) userName->{
sendMessage("User id is $userId and name is $userName"){
callback.invoke()
}
}
}
}
fun getToken(userId : String , callback:(String)->Unit)
fun getUserName(token : String , callback:(String)->Unit)
fun sendMessage(message : String , callback:(String)->Unit)
Callback hell

10. fun test(userId:String, callback:()->Unit){
getToken(userId) token-> {
getUserName(token) userName->{
sendMessage("User id is $userId and name is $userName"){
callback.invoke()
}
}
}
}
fun getToken(userId : String) : Single<String>
fun getUserName(token : String) : Single<String>
fun sendMessage(message : String)

11. fun test(userId:String){
getToken(userId)
.flatMap {
return@flatMap getUserName(it)
}
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe({
sendMessage("User id is $userId and name is $userName")
}, {
//error handling
})
}

12. fun sendMessage(userId:String){
getToken(userId)
.flatMap {
return@flatMap getUserName(it)
}
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe({
sendMessage("User id is $userId and name is $userName")
}, {
//error handling
})
}

13. fun test(userId:String){
getToken(userId)
.flatMap {
return@flatMap getUserName(it)
}
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe({
sendMessage("User id is $userId and name is $userName")
}, {
//error handling
})
}

14. fun sendMessage(userId:String){
1. val token = getToken(userId)
2. val userName = getUserName(token)
3. sendMessage("User id is $userId and name is $userName")
}
What we want
Sequential

15. Suspend
suspend fun getToken(userId : String) : String
suspend fun getUserName(token : String) : String
suspend fun sendMessage(message : String) : String
suspend fun test(userId:String){
val token = getToken(userId)
val userName = getUserName(token)
sendMessage("User id is $userId and name is $userName")
}

16. suspend fun getToken(userId : String) : String {
// do request & suspend
return token
}
suspend fun getUserName(token : String) : String
suspend fun sendMessage(message : String) : String
suspend fun test(userId:String){
val token = getToken(userId)
val userName = getUserName(token)
sendMessage("User id is $userId and name is $userName")

17. suspend fun getToken(userId : String) : String
suspend fun getUserName(token : String) : String
suspend fun sendMessage(message : String)
suspend fun test(userId:String){
val token = getToken(userId)
val userName = getUserName(token)
sendMessage("User id is $userId and name is $userName")
}
Like Regular code !!

18. suspend fun getToken(userId : String) : String
suspend fun getUserName(token : String) : String
suspend fun sendMessage(message : String)
suspend fun test(userId:String){
val token = getToken(userId)
val userName = getUserName(token)
sendMessage("User id is $userId and name is $userName")
}
Like Regular code !!

20. How does it work ??

21. Let’s get deeper

22. suspend fun getToken(userId : String) : String
public final getToken(Ljava/lang/String;Lkotlin/coroutines/experimental/Continuation;)Ljava/lang/Object
fun getToken(userId : String) : String
public final getToken(Ljava/lang/String;)Ljava/lang/String;
befroe

23. suspend fun getToken(userId : String) : String
public final getToken(Ljava/lang/String;Lkotlin/coroutines/experimental/Continuation;)Ljava/lang/Object
fun getToken(userId : String) : String
public final getToken(Ljava/lang/String;)Ljava/lang/String;
Kotlin bytecode for jvm

24. suspend fun getToken(userId : String) : String
public final getToken(Ljava/lang/String;Lkotlin/coroutines/experimental/Continuation;)Ljava/lang/Object
fun getToken(userId : String) : String
public final getToken(Ljava/lang/String;)Ljava/lang/String;
After

25. suspend fun getToken(userId : String) : String
public final getToken(Ljava/lang/String;Lkotlin/coroutines/experimental/Continuation;)Ljava/lang/Object
fun getToken(userId : String) : String
public final getToken(Ljava/lang/String;)Ljava/lang/String;
After

26. suspend fun getToken(userId : String) : String
public final getToken(Ljava/lang/String;Lkotlin/coroutines/experimental/Continuation;)Ljava/lang/Object
fun getToken(userId : String) : String
public final getToken(Ljava/lang/String;)Ljava/lang/String;

27. Continuation-passing style
In functional programming, continuation-passing style (CPS) is a style of
programming in which control is passed explicitly in the form of a continuation
fun test( ){
val token = requestToken()
val userId = getUserId(token)
}
fun test( ){
getToken { token->
val userId = getUserId(token)
}
}
Direct Style

28. Continuation-passing style
In functional programming, continuation-passing style (CPS) is a style of
programming in which control is passed explicitly in the form of a continuation
fun test( ){
val token = requestToken()
val userId = getUserId(token)
}
fun test( ){
getToken { token->
val userId = getUserId(token)
}
}
Direct Style
Continuation

29. Continuation-passing style
In functional programming, continuation-passing style (CPS) is a style of
programming in which control is passed explicitly in the form of a continuation
fun test( ){
val token = requestToken()
val userId = getUserId(token)
}
fun test( ){
getToken { token->
val userId = getUserId(token)
}
}

30. Continuation-passing style
In functional programming, continuation-passing style (CPS) is a style of
programming in which control is passed explicitly in the form of a continuation
fun test( ){
val token = requestToken()
val userId = getUserId(token)
}
fun test( ){
getToken { token->
val userId = getUserId(token)
}
}
CPS == Callback

31. How does it work
interface Continuation<in T> {
val context: CoroutineContext
fun resume(value: T)
fun resumeWithException(exception: Throwable)
}

32. class test(userId:String , sm : Continuation<Unit>) : Any{
val sm = CoroutineImpl {
fun doResume(...){
test(null,this)
}
var token : String
var userName : String
}
switch(sm.Label){
case 0:
sm.Label = 1
getToken(userId,sm)
break
case 1:
sm.Label = 2
getUserName(sm.token , sm)
break
case 2:
sm.Label = 3
sendMessage("User id is $userId and name is $userName")
break
}
}
suspend fun test(userId:String){
val token = getToken(userId)
val userName = getUserName(token)
sendMessage("User id is $userId and
name is $userName")
}

33. class test(userId:String , callback : Continuation<Unit>) : Any{
val sm = CoroutineImpl {
fun resume(...){
test(null,this)
}
var token : String
var userName : String
}
switch(sm.Label){
case 0:
sm.Label = 1
getToken(userId,sm)
break
case 1:
sm.Label = 2
getUserName(sm.token , sm)
break
case 2:
sm.Label = 3
sendMessage("User id is $userId and name is $userName")
break
}
}
suspend fun test(userId:String){
val token = getToken(userId)
val userName = getUserName(token)
sendMessage("User id is $userId and
name is $userName")
}

34. class test(userId:String , callback : Continuation<Unit>) : Any{
val sm = CoroutineImpl {
fun doResume(...){
test(null,this)
}
var token : String
var userName : String
}
switch(sm.Label){
case 0:
sm.Label = 1
getToken(userId,sm)
break
case 1:
sm.Label = 2
getUserName(sm.token , sm)
break
case 2:
sm.Label = 3
sendMessage("User id is $userId and name is $userName")
break
}
}
suspend fun test(userId:String){
val token = getToken(userId)
val userName = getUserName(token)
sendMessage("User id is $userId and
name is $userName")
}

35. class test(userId:String , callback : Continuation<Unit>) : Any{
val sm = CoroutineImpl {
fun doResume(...){
test(null,this)
}
var token : String
var userName : String
}
switch(sm.Label){
case 0:
sm.Label = 1
getToken(userId,sm)
break
case 1:
sm.Label = 2
getUserName(sm.token , sm)
break
case 2:
sm.Label = 3
sendMessage("User id is $userId and name is $userName")
break
}
}
suspend fun test(userId:String){
val token = getToken(userId)
val userName = getUserName(token)
sendMessage("User id is $userId and
name is $userName")
}
spending function

36. class test(userId:String , callback : Continuation<Unit>) : Any{
val sm = CoroutineImpl {
fun doResume(...){
test(null,this)
}
var token : String
var userName : String
}
switch(sm.Label){
case 0:
sm.Label = 1
getToken(userId, sm )
break
case 1:
sm.Label = 2
getUserName(sm.token , sm)
break
case 2:
sm.Label = 3
sendMessage("User id is $userId and name is $userName")
break
}
}
suspend fun test(userId:String){
val token = getToken(userId)
val userName = getUserName(token)
sendMessage("User id is $userId and
name is $userName")
}
Restore state

37. class test(userId:String , callback : Continuation<Unit>) : Any{
val sm = CoroutineImpl {
fun resume(...){
test(null,this)
}
var token : String
var userName : String
}
switch(sm.Label){
case 0:
sm.Label = 1
getToken(userId,sm)
break
case 1:
sm.Label = 2
getUserName(sm.token , sm)
break
case 2:
sm.Label = 3
sendMessage("User id is $userId and name is $userName")
break
}
}
suspend fun test(userId:String){
val token = getToken(userId)
val userName =
getUserName(token)
sendMessage("User id is $userId
and name is $userName")
}

38. Android

39. Retrofit
kotlin version 1.3
implementation 'com.jakewharton.retrofit:retrofit2-kotlin-coroutines-adapter:0.9.2'
kotlin version pre-1.3
implementation 'com.jakewharton.retrofit:retrofit2-kotlin-coroutines-experimental-adapter:1.0.0'
val retrofit = Retrofit.Builder()
.baseUrl("https://example.com/")
.addCallAdapterFactory(CoroutineCallAdapterFactory())
.build()

40. Retrofit
interface MyService {
@GET("/user")
fun getUser(): Deferred<User>
}

41. Retrofit
interface MyService {
@GET("/user")
fun getUser(): Deferred<User>
}

42. Retrofit
GlobalScope.launch(Dispatchers.IO) {
val data = APIRepo.getUser()
withContext(Dispatchers.Main) {
showMesssgae(data.await().message)
}
}

43. Retrofit
interface MyService {
@GET("/user")
fun getUser(): Call<User>
}

44. Retrofit
suspend fun <T> Call<T>.await(): T = suspendCancellableCoroutine { cont ->
cont.invokeOnCancellation {
if (cont.isCancelled) {
cont.cancel()
}
}
enqueue(object : Callback<T> {
override fun onFailure(call: Call<T>?, t: Throwable) {
cont.resumeWithException(t)
}
override fun onResponse(call: Call<T>?, response: Response<T>) {
if (response.isSuccessful) {
val body = response.body()
?: return cont.resumeWithException(NullPointerException())
cont.resume(body)
} else {
cont.resumeWithException(HttpException(response))
}
}
})
}

45. Retrofit
suspend fun <T> Call<T>.await(): T = suspendCancellableCoroutine { cont ->
cont.invokeOnCancellation {
if (cont.isCancelled) {
cont.cancel()
}
}
enqueue(object : Callback<T> {
override fun onFailure(call: Call<T>?, t: Throwable) {
cont.resumeWithException(t)
}
override fun onResponse(call: Call<T>?, response: Response<T>) {
if (response.isSuccessful) {
val body = response.body()
?: return cont.resumeWithException(NullPointerException())
cont.resume(body)
} else {
cont.resumeWithException(HttpException(response))
}
}
})
}

46. Retrofit
GlobalScope.launch(Dispatchers.IO) {
val data = APIRepo.getUser().await()
withContext(Dispatchers.Main) {
showMesssgae(data.message)
}
}

47. Retrofit
GlobalScope.launch(Dispatchers.IO) {
val data = APIRepo.getUser().await()
withContext(Dispatchers.Main) {
showMesssgae(data.message)
}
}
// Call<T>.await is extension function retrun data

48. Error handling
GlobalScope.launch(Dispatchers.IO) {
try {
val data = APIRepo.getUser()
withContext(Dispatchers.Main) {
showMesssgae(data.message)
}
}catch(e : Exception){
// error
}
}

49. How to cancel ?
val job = GlobalScope.launch(Dispatchers.IO) {
val data = APIRepo.getUser()
withContext(Dispatchers.Main) {
showMesssgae(data.message)
}
}
job.cancel()
// RxJava Disposable

50. How to cancel ?
job.cancel()

51. Job Job …….. n
class MainActivityTest : AppCompatActivity(),
CoroutineScope {
private val job = Job()
override val coroutineContext: CoroutineContext
get() = job + Dispatchers.Main
override fun onDestroy() {
super.onDestroy()
job.cancel()
}
GlobalScope.launch(coroutineContext)
{
//do async
}
GlobalScope.launch(coroutineContext) {
//do async
}
GlobalScope.launch(coroutineContext) {
//do async
}

52. Concurrently
GlobalScope.launch(Dispatchers.IO) {
val data = APIRepo.getUser() // Deferred
withContext(Dispatchers.Main) {
showMesssgae(data.await().message)
}
}

53. Concurrently
GlobalScope.launch(Dispatchers.IO) {
val data = APIRepo.getUser() // Deferred
val dataNew = APIRepo.getUserNew() // Deferred
val dataNewTwo = APIRepo.getUserNewTwo() // Deferred
withContext(Dispatchers.Main) {
showMesssgae(data.await().message)
}
}

54. Concurrently
GlobalScope.launch(Dispatchers.IO) {
val data = APIRepo.getUser() // Deferred
val dataNew = APIRepo.getUserNew() // Deferred
val dataNewTwo = APIRepo.getUserNewTwo() // Deferred
withContext(Dispatchers.Main) {
showMesssgae(data.await().message)
}
}

55. Concurrently
GlobalScope.launch(Dispatchers.IO) {
val data = APIRepo.getUser() // Deferred
val dataNew = APIRepo.getUserNew() // Deferred
val dataNewTwo = APIRepo.getUserNewTwo() // Deferred
withContext(Dispatchers.Main) {
showMesssgae(data.await().message,dataNew.await().message,dataNewTwo.await().message)
}
}

56. Performance

57. Reference :
https://proandroiddev.com/kotlin-coroutines-vs-rxjava-an-initial-performance-test-68160cfc6723

58. GlobalScope.launch(Dispatchers.IO) {
val data = APIRepo.getUser() // Deferred
withContext(Dispatchers.Main) {
showMesssgae(data.await().message)
}
}

60. Recap
● Asynchronous
● Apk Siz & Method count
● Performance
● Readable
● Cost

61. Recap
● Asynchronous
● Apk size & Method count
● Performance
● Readable
● Cost

62. Recap
● Asynchronous
● Apk Siz & Method count
● Performance
● Readable
● Cost

63. Recap
● Asynchronous
● Apk Siz & Method count
● Performance
● Readable
● Cost

64. Recap
● Asynchronous
● Apk Siz & Method count
● Performance
● Readable
● Cost

65. Q & A
Thank you

66. Reference
https://kotlinlang.org/docs/reference/coroutines-overview.html
https://www.youtube.com/watch?v=_hfBv0a09Jc
https://www.youtube.com/watch?v=YrrUCSi72E8&t=707s