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Architectures with Kotlin
Multiplatform
Jitin Sharma
GO-JEK
@_jitinsharma
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Most popular among Android Developers
Was designed with platform agnostic behaviour.
Has a lot of features which can targeted outside
JVM environment.
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JVM/Server Android .kts Javascript Native
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Kotlin Native
Can target iOS, Windows, MacOS, Linux etc
No Runtime environment
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Interop
C/Objective C interop provided
System frameworks are automatically imported
in case of iOS.
Types are mapped with Swift/Objective C.
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Multiplatform
One Language to rule them all
Started with Kotlin 1.2
Still in experimental phase.
Built in tooling with IntellijIDEA.
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“Multiplatform is not cross platform”
–Kotlin
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common
android iOS js server
project
- Presentation logic
- ui-logic
- Data models
- Helper/utilities
- Networking
- Storage
- Data models
- Networking?
- Storage?
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onStart
onResume
…
viewDidLoad
viewDidAppear
…
Async networking
Async storage
Kotlin Swift
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app
commonMain
main iosMain
iosApp
.kt,xml
.kt
.kt
Imports common
libraries
Imports iOS
libraries
Builds Android app
Builds .framework
.swift, xib
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Common Logic
dependencies {
implementation kotlin('stdlib-common')
}
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val names = mutableListOf("Bumblebee", "Optimus Prime", "Megatron")
names.sort()
Foo.kt
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expect fun > MutableList.sort(): Unit
val names = mutableListOf("Bumblebee", "Optimus Prime", "Megatron")
names.sort()
public actual fun > MutableList.sort(): Unit {
if (size > 1) java.util.Collections.sort(this)
}
MutableCollectionsJVM.kt
CollectionsH.kt
Foo.kt
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expect & actual
expect fun …
expect val…
expect class…
Actual Platform
declarations
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Client Server
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NetworkClient.kt
class NetworkClient {
private val client = HttpClient()
fun get(url: String, callback: (String) -> Unit) {
GlobalScope.launch(ApplicationDispatcher) {
val result: String = client.get { url(url) }
callback(result)
}
}
}
internal expect val ApplicationDispatcher: CoroutineDispatcher
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internal expect val ApplicationDispatcher: CoroutineDispatcher
internal actual val ApplicationDispatcher: CoroutineDispatcher = Dispatchers.Default
AndroidDispatcher.kt
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internal expect val ApplicationDispatcher: CoroutineDispatcher
import platform.darwin.dispatch_async
import platform.darwin.dispatch_get_main_queue
import platform.darwin.dispatch_queue_t
internal actual val ApplicationDispatcher: CoroutineDispatcher = NsQueueDispatcher(dispatch_get_main_queue()
internal class NsQueueDispatcher(private val dispatchQueue: dispatch_queue_t) : CoroutineDispatcher() {
override fun dispatch(context: CoroutineContext, block: Runnable) {
dispatch_async(dispatchQueue) {
block.run()
}
}
}
IOSDispatcher.kt
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Serialization
@Serializable
data class AllData(
val avatar_url: String?,
val bio: String?,
val blog: String,
....
)
import kotlinx.serialization.*
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Persistence - SQLDelight
CREATE TABLE Photos (
id INTEGER NOT NULL,
title TEXT NOT NULL
);
insert:
INSERT INTO Photos (id, title) VALUES (?, ?);
getAll:
SELECT * FROM Photos;
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Persistence
expect val db: Database
db.photoQueries.getAll() -> List
//iOS
actual val db = Database(NativeSqliteDriver(Database.Schema, "photo.db"))
//Android
actual val db = Database(AndroidSqliteDriver(Database.Schema, context, “photo.db"))
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interface MainView {
fun displayData(data: DisplayData)
fun showLoader()
fun hideLoader()
}
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class DataRepository {
private val api = NetworkApi("https://github.com")
fun getData(username: String, callback : (Data) -> Unit) {
val data = api.getAll(username) {
callback(it)
}
}
}
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class MainPresenter(private val view: MainView,
private val repository: DataRepository) {
fun loadData(userName: String) {
if (userName.isNullOrEmpty()) {
view.showError(USER_NAME_NOT_VALID)
} else {
view.showLoader()
repository.getData(userName) {
showData()
view.hideLoader()
}
}
}
}
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extension ViewController: MainView {
func showLoader() {
activityIndicator.startAnimating()
}
func hideLoader() {
activityIndicator.stopAnimating()
}
func displayData(data: DisplayData) {
....
}
}
ViewController.swift
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PhotoListState
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PhotoListState
Store
States Reducers Middlewares
Action
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data class Photo(
@SerializedName("id")
val id: String,
@SerializedName("title")
val title: String,
......
)
gson serialization
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expect val store: Store
expect class AppState : StateType
expect fun appReducer(action: Action, state: AppState?): AppState
class LoadRecentPhotos : Action
class SerializeResponse(val response: String) : Action
Actions.kt
Common
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actual val store: Store = Store(
state = AppState(),
reducer = ::appReducer,
middleware = listOf(networkMiddleWare, databaseMiddleWare)
)
actual data class AppState(val photoListState: PhotoListState? = null) : StateType
actual fun appReducer(action: Action, state: AppState?): AppState {
return AppState(photoListState = photoListReducer(action, state?.photoListState))
}
Android
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class MainActivity : AppCompatActivity(), StoreSubscriber {
override fun newState(state: PhotoListState?) {
state.shouldUpdate {
val photos = it.photos
setImageAdapter(photos)
}
}
}
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Performance
Generated framework binaries are smaller in size.
Few extra classes are generated for various kotlin
types
For Android/JVM there is not much impact.
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Debugging
For Android/JVM projects, both common code and
android code can be debugged right from IDE.
For iOS, generated framework files can be
debugged accordingly.
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Testing
Shared code test cases can be written out of
IntelliJ using kotlin.test
Platform specific execution using platform test
libraries.
Existing platform libraries(espresso, xctest) can
still be used.
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DIY Multiplatform Libraries
common
android
iOS
./gradlew build library.jar
library.framework
Multiplatform Publishing
library-common.jar
library-android.jar
library-ios.klib
.module
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DIY Multiplatform Libraries
common
android
iOS
./gradlew build library.jar
library.framework
Multiplatform Publishing
library-common.jar
library-android.jar
library-ios.klib
.module
maven, pod
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What’s NOT great
Dependence of Multiplatform libs for better code
sharing
Still experimental
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What’s great
Language - Kotlin
No external dependencies as in custom runtime/
VM
Pragmatic APIs
Platform specific libs with common Kotlin code
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Multiplatform Libraries
https://github.com/ktorio/ktor
https://github.com/Kotlin/kotlinx.coroutines
https://github.com/square/sqldelight/
https://github.com/russhwolf/multiplatform-settings
https://github.com/ReKotlin/rekotlin-multiplatform
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Thanks
@_jitinsharma