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KotlinConf 2018
Android ฤ
Akira Iwaya, LINE Corp.
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Who am I
• ؠ୩໌ɹ(@hoshi_gaki)
• LINE LIVE Android
• ϦϚΠϯ͘Μ
• αʔόʔαΠυKotlinͷݟʗKotlin
ͰClova Skill Awardઓ0
0 https://engineering.linecorp.com/ja/blog/detail/346
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LINE LIVE
• 30% Kotlin and increasing
• In LINE app as submodule
• MVVM + Partially Redux
• Dagger2, RxJava2, AutoDispose, ExoPlayer, ...
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ϦϚΠϯ͘Μ
• Reminder bot
• Almost Kotlin
• Spring Boot 2
• MyBatis + MySQL, Redis
• App(1) + DB(1)
• 452K friends
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Android sessions at KotlinConf
2018
• Android Suspenders (Christ Banes)
• Shaping your app's architecture with Kotlin and Architecture
Components
• Android KTX: A dash of Kotlin makes all the difference!
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Android Suspenders2
Christ Bane
• Why coroutines
• How to use coroutines in Android
• Jobs, Scopes, Reactivity
• Cancellations, Exceptions, Dispatchers, Channels (skip)
• Android callback -> suspend functions (skip)
2 https://chris.banes.me/talks/2018/android-suspenders/
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• Android's main thread:
60Hz, 16ms / 90Hz, 12ms / 120Hz, 8ms
• AsyncTask, Executors, Loaders, Future, Rx, Coroutine
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So why coroutines?
• Great for I/O tasks
• Scale on limited hardware
• Easier development model
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kotlinx-coroutines-core
kotlinx-coroutines-android
kotlinx-coroutines-rx2
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How to use coroutines in Android
class ShowDetailsViewModel: ViewModel() {
val showRepository: ShowRepository = // ...
val state: LiveData
init {
refresh()
}
private fun refresh() {
launch {
showRepository.updateShow(showId)
// update view state
}
}
}
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Cancellation
class ShowDetailsViewModel: ViewModel() {
private var updateShowJob: Job? = null
private fun refresh() {
updateShowJob = launch {
showRepository.updateShow(showId)
// update view state
}
}
override fun onCleared() {
updateShowJob?.cancel()
}
}
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!
class ShowDetailsViewModel: ViewModel() {
private var updateShowJob: Job? = null
private var updateEpisodesJob: Job? = null
private var updateCastJob: Job? = null
private fun refresh() {
updateShowJob = launch { ... }
updateEpisodesJob = launch { ... }
updateCastJob = launch { ... }
}
override fun onCleared() {
updateShowJob?.cancel()
updateEpisodesJob?.cancel()
updateCastJob?.cancel
}
}
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Jobs can have parent-child relationship !
private val job = Job()
private fun refresh() {
launch(parent = job) {
showRepository.updateShow(showId)
// update view state
}
}
override onCleared() {
job.cancel()
}
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launch(parent = job) {
updateShow(showId)
}
suspend fun updateShow(showId: Long) {
val local = async { // no parent
localShowStore.getShow(showId)
}
val remote = async [ // no parent
remoteSource.getShow(showId)
]
val merged = mergeShow(local.await(), remote.await())
localShowStore.saveShow(merged)
}
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CoroutineScope
• Two coroutines does not get cancelled when parent job is
cancelled !
• launch, async is deprecated in v0.26
• launch, async becomes instance method of
CoroutineScope
• Must provide default context
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class ShowDetailsViewModel: ViewModel(), CoroutineScope {
private val job = Job()
override val coroutineContext: CoroutineContext
get() = job + Dispatchers.Main
private fun refresh() {
launch(context = coroutineContext) {
showRepository.updateShow(showId)
...
}
}
override onCleared() {
super.onCleared()
job.cancel()
}
}
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!
suspend fun updateShow(showId: Long) = coroutineScope {
val local = async { // will be cancelled on job.cancel()
localShowStore.getShow(showId)
}
val remote = async [ // will be cancelled on job.cancel()
remoteSource.getShow(showId)
]
val merged = mergeShow(local.await(), remote.await())
localShowStore.saveShow(merged)
}
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Reactivity
Coroutines can replace Single / Maybe / Completable
interface RemoteService {
@GET("/trendingshows")
fun trendingShows(): Single>
}
service.trendingShows()
.scheduleOn(Schedulers.io())
.subscribe(::onTrendingLoaded, ::onError)
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With kotlinx-coroutines-rx2
interface RemoteService {
@GET("/trendingshows")
fun trendingShows(): Single>
}
val shows = withContext(IO) {
service.trendingShows().await()
}
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Coming to Retrofit soon
interface RemoteService {
@GET("/trendingshows")
suspend fun trendingShows(): List
}
val shows = withContext(IO) {
service.trendingShows()
}
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Related sessions
• Exploring Coroutines in Kotlin3
• Kotlin Coroutines in Practice4
• Coroutines and Reactive Programming - friends or foes?5
5 https://youtu.be/yoLh4sd1CWI
4 https://youtu.be/a3agLJQ6vt8
3 https://youtu.be/jT2gHPQ4Z1Q
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Shaping your app's architecture with Kotlin and Architecture Components6
Florina Muntenescu
• Why using coroutines
• Where to using coroutines
• How to using coroutines
• Java
• Type Safety - Inner class (Kotlin 1.3)
6 https://youtu.be/Sy6ZdgqrQp0
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Why using coroutines
• Ease of learning
• Single/Maybe/Completable -> suspend fun
• Streams of data (Channel)
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Where to use coroutines
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How to using coroutines - API
retrofit2-kotlin-coroutines-adapter
@POST("api/v2/comments")
fun comment(@Body comment: NewCommentRequest): Deferred>
• RemoteDataSource returns Result
sealed class Result {
data class Success(val data: T): Result()
data class Error(val exception: Exception): Result
}
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class CommentsRemoteDataSource(private val Service: RetrofitService) {
suspend fun comment(commentBody: String) = safeApiCall(
call = { postComment(commentBody) },
errorMessage = "Unable to post commment"
)
}
suspend fun safeAPiCall(
call: suspend () -> Result // suspend lambda
errorMessage: String
): Result = return try {
call()
} catch(e: Exception) {
Result.Error(IOException(errorMessage, e))
}
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Java
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class ShotsRepository(private val dataSource: XXXDataSource) {
suspend fun search(query: String): Result> =
remoteDataSource.search(query)
}
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shotsRepository.search(query,
new Continuation>>() {
@NotNull
@Override
public CoroutineContext getContext() {
return null;
}
@Override
public void resume(Result> result) {}
@Override
public void resumeWithException(@NotNull Throwable throwable) {}
}
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A Good enough compromise - Callback
class ShotsRepository(private val dataSource: XXXDataSource) {
private val inflight = mutableMapOf()
fun search(
query: String,
onResult: (Result>) -> Unit)
: Result> {
inflight[id] = launchSearch(query, onResult)
}
fun cancel() {
inflight.values.forEach { it.cancel() }
inflight.clear()
}
}
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Type Safety - Inline Class
class CommentsRepository(...) {
suspend fun postStoryComment(
body: String,
storyId: Long,
userId: Long
): Result { ... }
suspend fun postReplyComment(
body: String,
parentCommentId: Long,
userId: Long
): Result
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Type Safety - Inline Class
class CommentsRepository(...) {
suspend fun postStoryComment(
body: String,
storyId: StoryId,
userId: Long
): Result { ... }
suspend fun postReplyComment(
body: String,
parentCommentId: CommentId,
userId: Long
): Result
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data class StoryId(val id: Long)
• Extra object creation occurs (Runtime overhead)
• Primitive types are heavily optimized by the runtime
inline class StoryId(val id: Long)
• From Kotlin 1.3
• An inline class must have a single property initialized in the
primary constructor
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UseCase - invoke operator
• A use case should have single responsibility
• UseCase should have only one public method
class PostStoryCommentUseCase(repository: XXXRepository) {
suspend fun postStoryComment(body: String, id: Long): Result
}
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• By implementing invoke operator
• Callers doesn't care how this is implemented, even nor
method name
class PostStoryComment(...) {
suspend operator fun invoke(body: String, id: Long): Result
}
// Caller side
val postStoryComment = ...
val result = postStoryComment(comment, id)
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bit.ly/livedata-events
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Modular, extensible architecture
based on the
architecture components and
Kotlin
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Android KTX: A dash of Kotlin makes all the difference!7
Dan Kim
• KTX is 1.0 with Android X (skip)
• Various extensions (1ݸ)
• How to contribute AOSP (skip)
7 https://www.youtube.com/watch?v=LP3PaPrIFHo
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// added in API level 11
view.addOnLayoutChangeListener(object: View.OnLayoutChangeListener {
override fun onLayoutChange(
view: View?
left: Int,
top: Int,
right: Int,
bottom: Int,
oldTop: Int,
oldRight: Int,
oldBottom: Int
) {
doSomething()
}
})
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// KTX
view.doOnNextLayout { doSomething() }
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