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Experiments with
Kotlin Multiplatform
AndroidHeads Vienna 2019/04/04
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What is Kotlin
Multiplatform?
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JVM Native JavaScript
Kotlin everywhere
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Multiplatform Project
Compilation Targets
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plugins {
id 'kotlin-multiplatform' version '1.3.20'
}
kotlin {
android()
iosX64()
…
}
Multiplatform Project Native App
commonMain
androidMain
iosMain
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expect - actual
common
expect fun logDebug(tag: String, message: String)
import android.util.Log
actual fun logDebug(tag: String, message: String) {
Log.d(tag, message)
}
actual fun logDebug(tag: String, message: String) {
println("${tag} : ${message}")
}
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Goal: Develop App with Kotlin
Multiplatform
• Load data from Web-API (Github Jobs API)
• Display job information in a list
• Persist job data for offline availability
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UI
Activities, Fragments, Views
UI
ViewController
Presenter Presenter
UseCases UseCases
Repository Repository
API Persistance API Persistance
Utils
Utils
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UI
Activities, Fragments, Views
UI
ViewController
Presenter
UseCases
Repository
API Persistance
Utils
Shared
Library
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Load Data from API
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Load Data from API
Engine
ThreadPool with HttpURLConnections
Engine
Asynchronous NSURLSession internally
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Load Data from API
@Serializable
data class JobPositionDto(
@SerialName(“id")
val id: String,
@SerialName("company")
val company: String,
@SerialName("location")
val location: String,
@SerialName("title")
val title: String,
@SerialName("type")
val type: String
)
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Persist Data
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Repository
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UI
Activities, Fragments, Views
UI
ViewController
Presenter
UseCases
Repository
API Persistance
Utils
Shared
Library
Create instance of presenter
Call getJobList() in Lifecycle method
Implement render() of JobListView
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Presenter - common
class JobsListPresenter(private val view: JobsListView) : BasePresenter(view) {
private val repository = JobPositionRepositoryImpl(GithubJobsApi())
fun getJobsList() {
view.render(UiState.Loading())
launch(IoDispatcher) {
repository.getJobsList().fold({
view.render(UiState.Success(it))
}, {
view.render(UiState.Error(Throwable("Loading Jobs failed")))
})
}
}
}
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common
interface JobsListView: BaseView {
fun render(uiState: UiState>)
}
class MainActivity : AppCompatActivity(), JobsListView {
…
override fun render(uiState: UiState>) {
when (uiState) {
is UiState.Success -> {
displayJobList(uiState.data)
}
is UiState.Loading -> {
displayProgress()
}
is UiState.Error -> {
displayError(uiState.throwable)
}
}
…
}
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common
interface JobsListView: BaseView {
fun render(uiState: UiState>)
}
class ViewController: UIViewController, UITableViewDelegate,
UITableViewDataSource, JobsListView {
…
func render(uiState: UiState) {
if(uiState is UiState.Success){
let state = uiState as! UiState.Success
displayJobList(jobs: state.data as! [JobPosition])
}
if(uiState is UiState.Loading){
displayProgress()
}
if(uiState is UiState.Error){
let state = uiState as! UiState.Error
displayError(error: state.throwable as! KotlinThrowable)
}
}
…
}
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No content
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Ready for Production?
Sharing pure logic
Sharing architecture
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• Experimental: Expect lots of changes
• Very little documentation, blogposts, samples, …
• Only Single-Threaded Coroutines in the common code
• Not perfect Swift - Kotlin Interoperability
• iOS debugging of the shared library not possible
• Important libraries for the common module still missing (e.g.
Date)
Sharing architecture
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Summary
• Kotlin can run everywhere
• Multiplatform Projects: More that one compilation target
• Mobile Code Sharing: Everything except the UI and some
platform specific functionality can be shared
• Sample Application “Kotlin MPP Jobs”
• Production-ready only for simple use cases
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Resources
• https://github.com/Lukle/Kotlin-mpp-jobs
• @lukleDev on Twitter