The Hitchhikers Guide Through Kotlin Multiplatform Extended

Since the early days of mobile that we keep seeing new frameworks being designed to overcome one of the biggest challenges:
- How can I develop for both Android and iOS?

Although it’s initial promises, when we talk about performance, maintainability or even customization we keep discarding these solutions and we always choose native.

Fast forward to the present, and now we have two new languages: Android is Kotlin first and iOS, Swift. And if you put them side by side you can see a lot of similarities between both what will ease switching between one to the other if you have to develop for both platforms.

But what I told that you could just develop in Kotlin and run it seamlessly on all devices? Here comes Kotlin Multiplatform!

Transcript

1. The Hitchhikers Guide Through The Hitchhikers Guide Through Kotlin Multiplatform Kotlin Multiplatform @cafonsomota revised and updated edition revised and updated edition
2. speakerdeck.com/cmota/ the-hitchhikers-guide-through-kotlin-multiplatform-extended @cafonsomota
4. a brief history of time “In the beginning the Universe was created. This had made many people angry and has been widely regarded as a bad move.”
5. android iOS
6. Dark Theme
7. android iOS
8. Photo by Fabian Grohs on Unsplash
9. Photo by Fabian Grohs on Unsplash a wild application idea appears! develop it for Android and iOS.
10. -hire a team of specialised developers -define requirements -design mockups for both platforms -plan features development -start development/ write unit tests -write t-specs for SQA validation -cross-checking validation between both platforms (or jacks) Steps
11. ~2xthe team the cost the status meetings required the time spent on development the time spent on testing native the time spent on bug fixing
12. Photo by Fabian Grohs on Unsplash a wild application idea appears! develop it for Android and iOS and web.
13. ~3xthe team the cost the status meetings required the time spent on development the time spent on testing the time spent on bug fixing
15. let’s find a solution that works on all platforms.
16. 2008 2012 2018 2013 2011 2017 2006 2010 2009 2015 * Kotlin Multiplatform *
17. - smaller team - typically half of the cost needed on native - small learning curve for web developers (advantages) Cross-platform
18. - chained to the framework implementation of UI - new updates from the OS will take time to adopt - performance is not the same - some native code might need to be written - OS/ device features are dependent on the fw support - dart (flutter) is not widely used language (for now) (disadvantages) Cross-platform
19. how can we have the best of both worlds?
20. how can we have the best of both worlds?
21. kotlin “42.”
23. - developed by JetBrains - open source - concise, safe, interoperable, tool-friendly - supported/ used by Google for Android Development - it’s more than “just for Android” Kotlin Server-side Android Kotlin JS Native
24. Mutability etc. Null safety Default values Type inference String interpolation when Collections
25. NullPointerException NullPointerException NullPointerException NullPointerException NullPointerException NullPointerException NullPointerException NullPointerException TransactionTooLargeException
26. public class Conference { private String mName; private String mLocal; private List<String> mTechs; public Conference(String name, String local, List<String> techs) { mName = name; mLocal = local; mTechs = techs; } public String getName() { return mName; } public void setName(String name) { Conference.java (less code) Concise
27. data class Conference (val name: String, val location: String, val techs: List<String>) (less code) Concise Conference.kt
28. Less bugs! more free time (and happier team… and management) (less code) Concise
29. -getOrElse() -find() -filter() -filterNot() -filterNotNull() -flatMap() -mapNotNull() -all() -any() -sumBy() -zip() -… -take() -takeLast() -sortBy() -sortByDescending() -groupBy() -map() (collections) Language features
30. > [1, null, 2, null, 3, 4, 5, 6, 7, 8, 9] (collections) Language features output mutableListOf(1, null, 2, null, 3, 4, 5, 6, 7, 8, 9)
31. > [1, 2, 3, 4, 5, 6, 7, 8, 9] (collections) Language features output mutableListOf(1, null, 2, null, 3, 4, 5, 6, 7, 8, 9) .filterNotNull()

32. > [2, 4, 6, 8] .filter { it % 2 == 0 }
 (collections) Language features output mutableListOf(1, null, 2, null, 3, 4, 5, 6, 7, 8, 9) .filterNotNull()

33. > [8, 6, 4, 2] .sortedDescending() (collections) Language features output .filter { it % 2 == 0 }
 mutableListOf(1, null, 2, null, 3, 4, 5, 6, 7, 8, 9) .filterNotNull()

34. - small learning curve involved - easily to go from JavaScript/ Swift into Kotlin and back (from a developers’ point of view) Easy to learn
35. var variable = 42 variable = 1 let value = 42 var variable = 42 variable = 1 val value = 42 *adapted from http://nilhcem.com/swift-is-like-kotlin/ (variables and constants) Kotlin vs Swift Kotlin Swift
36. fun greet(name: String, day: String): String { return "Hello $name, today is $day." } greet(“Porto", “Saturday") *updated from http://nilhcem.com/swift-is-like-kotlin/ func greet(_ name: String,_ day: String) -> String { return "Hello \(name), today is \(day)." } greet(“Porto", “Saturday") Kotlin Swift (functions) Kotlin vs Swift
37. kotlin multiplatform “‘Resistance is useless!’ How can anyone maintain a positive mental attitude if you’re saying things like that?”
38. K otlin multiplatform using kotlin in projects that target more than one platform
39. (advantages) - language features - kotlin first! - low risk - you decide what’s worth to share across projects - interoperability - consistency across platforms - strong community support Kotlin Multiplatform
40. first reaction
41. view view view view model parser network presentation presentation presentation presentation network network network parser parser parser model model model presentation presentation presentation desktop web iOS android
42. business logic business logic business logic model parser network presentation model parser network presentation model parser network presentation model parser network presentation business logic view view view view desktop web iOS android
43. android iOS web desktop model parser network presentation common view view view view java/kotlin objective-c/ swift (kotlin) JS supported in jvm
44. src/ androidMain/ androidTest/ iosMain/ iosTest/ commonMain/ commonTest/ app/ project structure
45. but how can they expect to communicate?
46. declared at common module expect declared at android module actual declared at iOS module declared at …
47. we want a platform-specific value for name
48. expect object Platform { val name: String } commonMain src/commonMain/sample/Platform.kt
49. commonMain src/commonMain/sample/Platform.kt - define actual on android - define actual on iOS targets: android and iOS expect object Platform { val name: String }
50. src/iOSMain/sample/Platform.kt actual object Platform { actual val name: String = "Android" } actual object Platform { actual val name: String = "iOS" } src/androidMain/sample/Platform.kt platform-dependent code
51. IntelliJ will ask you declare the implementations for actual
52. *.kt common expect JVM actual *.kt, *.java, *.jar Native actual *.kt, *C, Swift, Framework JS actual *.kt, *.js, NPM
53. medium.com/@cafonsomota
54. show me the code!
55. demo "For a moment, nothing happened. Then, after a second or so, nothing continued to happen.”
56. github.com/cmota/droidconLX
57. - user interface - RecyclerView and more (Android) - UITableViewController and more (iOS) - multiple network request - parse response objects - store on local database - notify the UI - that there’s new content available to be draw - reload list project structure
58. android iOS Room CoreData Retrofit Alamofire GSON/ Moshi JSONSerialization MVP, MVVM, MVI MVVM, ELM RxJava RxSwift Tests Tests Activity UIViewController RecyclerView UITableView
59. Room CoreData Retrofit Alamofire GSON/ Moshi JSONSerialization MVP, MVVM, MVI MVVM, ELM RxJava RxSwift Tests Tests Activity UIViewController RecyclerView UITableView android iOS
60. Room CoreData Retrofit Alamofire GSON/ Moshi JSONSerialization MVP, MVVM, MVI MVVM, ELM RxJava RxSwift Tests Tests Activity UIViewController RecyclerView UITableView android iOS Activity UIViewController RecyclerView UITableView unnecessary duplication
61. SQLDelight ktor kotlinx.serialization MVP kotlinx.coroutines kotlin.test android iOS Activity UIViewController RecyclerView UITableView
62. multiplatform httpClient ktor SQLDelight android kotlinx.serialization SQLDriver dispatcher view presenter presenter model GetSchedule GetSpeakers
63. multiplatform httpClient ktor SQLDelight iOS model kotlinx.serialization GetSchedule GetSpeakers SQLDriver dispatcher view presenter presenter
64. multiplatform network database android parser presenter presenter view platform domain specific model
65. class SessionizeAPI(engine: HttpClientEngine) { private val client = HttpClient(engine) { install(JsonFeature) { serializer = KotlinxSerializer() } } suspend fun fetchSpeakers(): List<SpeakerEntity> { val response = client.get<HttpResponse>{ url ("$URL")} val json = response.readText() return Json.parse(SpeakerEntity.serializer().list, json) } } network src/commonMain/data/SessionizeAPI.kt ktor multiplatform network database android parser view platform specific presenter presenter domain model common (shared) code
66. kotlinx.serialization network src/commonMain/data/SessionizeAPI.kt class SessionizeAPI(engine: HttpClientEngine) { private val client = HttpClient(engine) { install(JsonFeature) { serializer = KotlinxSerializer() } } suspend fun fetchSpeakers(): List<SpeakerEntity> { val response = client.get<HttpResponse>{ url ("$URL")} val json = response.readText() return Json.parse(SpeakerEntity.serializer().list, json) } } multiplatform network database android parser view platform specific presenter presenter domain model
67. json response [{ "id": "2bc1e95f-1243-4ad0-8a11-75541fee10e0", "firstName": "Carlos", "lastName": "Mota", "fullName": "Carlos Mota", "bio": "… GDG Coimbra organizer and Kotlin evangelist, he also has a huge passion for travel, photography, space and the occasional run.", "tagLine": "Lead Software Engineer at WIT Software", "profilePicture": “https://sessionize.com/imag...7ef8707ae.jpg”, "sessions": [{ "id": 131513, "name": "The Hitchhikers Guide Through Kotlin Multiplatform" }], … },… https://sessionize.com/api/v2/3hvwlgcc/view/speakers
68. json response [{ "id": "2bc1e95f-1243-4ad0-8a11-75541fee10e0", "firstName": "Carlos", "lastName": "Mota", "fullName": "Carlos Mota", "bio": "… GDG Coimbra organizer and Kotlin evangelist, he also has a huge passion for travel, photography, space and the occasional run.", "tagLine": "Lead Software Engineer at WIT Software", "profilePicture": “https://sessionize.com/imag...7ef8707ae.jpg”, "sessions": [{ "id": 131513, "name": "The Hitchhikers Guide Through Kotlin Multiplatform" }], … },… https://sessionize.com/api/v2/3hvwlgcc/view/speakers
69. kotlinx.serialization src/commonMain/data/entities/SpeakerEntity.kt multiplatform network database android parser view platform specific presenter presenter domain model parser @Serializable data class SpeakerEntity ( val id: String, val firstName: String, val lastName: String, val fullName: String, val bio: String, val tagLine: String, val profilePicture: String, val sessions: List<SessionShortEntity>, val isTopSpeaker: Boolean, val links: List<String>, val questionAnswers: List<String>, val categories: List<String>)
70. kotlinx.serialization src/commonMain/data/entities/SpeakerEntity.kt multiplatform network database android parser view platform specific presenter presenter domain model parser @Serializable data class SpeakerEntity ( val id: String, val firstName: String, val lastName: String, val fullName: String, val bio: String, @SerialName("tagLine") val jobTitle: String, val profilePicture: String, val sessions: List<SessionShortEntity>, val isTopSpeaker: Boolean, val links: List<String>, val questionAnswers: List<String>, val categories: List<String>)
71. database CREATE TABLE SpeakerModel ( id TEXT NOT NULL PRIMARY KEY, speaker TEXT as Speaker NOT NULL ); insertOrReplaceSpeaker: INSERT OR REPLACE INTO SpeakerModel(id, speaker) VALUES (?, ?); selectAllSpeakers: SELECT * FROM SpeakerModel; SQLDelight src/commonMain/sqldelight/data/model/SpeakerModel.sq multiplatform network database android parser view platform specific presenter presenter domain model
72. database SQLite SQLDelight multiplatform network database android parser view platform specific presenter presenter domain model
73. database SQLite Compiler Generated code SQLDelight multiplatform network database android parser view platform specific presenter presenter domain model
74. database Generated code SQLDelight multiplatform network database android parser view platform specific presenter presenter domain model
75. app/build/sqldelight/ScheduleDb/data/app/ScheduleDbImpl.kt database class SpeakerModelQueriesImpl(private val db: ScheduleDbImpl, private val driver: SqlDriver) : TransacterImpl(driver), SpeakerModelQueries { … override fun insertOrReplaceSpeaker(id: String, speaker: Speaker) { driver.execute(2113668020, """INSERT OR REPLACE INTO SpeakerModel(id, speaker) |VALUES (?1, ?2)""", 2) { bindString(1, id) bindString(2, db.SpeakerModelAdapter.speakerAdapter.encode(speaker)) } notifyQueries(2113668020, {db.speakerModelQueries.selectAllSpeakers}) } } generated class SQLDelight multiplatform network database android parser view platform specific presenter presenter domain model
76. model class SpeakerDao(database: ScheduleDb) { private val db = database.speakerModelQueries internal fun insertOrReplace(speaker: Speaker) { db.insertOrReplaceSpeaker( id = speaker.id, speaker = speaker) } internal fun getAllSpeakers(): List<Speaker> { val data = db.selectAllSpeakers().executeAsList() … src/commonMain/domain/dao/SpeakerDao.kt multiplatform network database android parser view platform specific presenter presenter domain model
77. model @Serializable data class Speaker ( val id: String, val fullName: String, val bio: String, val tagLine: String, val profilePicture: String, val sessions: List<Info>, val categories: List<String>) fun SpeakerEntity.toSpeaker() = Speaker( id = id, fullName = fullName, bio = bio, …) src/commonMain/domain/model/Speaker.kt multiplatform network database android parser view platform specific presenter presenter domain model
78. domain class GetSpeakers(val api: SessionizeAPI, val dao: SpeakerDao) { suspend operator fun invoke(onSuccess: (List<Speaker>) -> Unit, onFailure: (Exception) -> Unit) { try { val result = api.fetchSpeakers() val speakers = Speaker.toSpeaker(result) dao.insertOrReplace(speakers) coroutineScope { launch(uiDispatcher) { onSuccess(speakers) } } } catch (e: Exception) { onFailure(e) } src/commonMain/domain/GetSpeakers.kt multiplatform network database android parser view platform specific presenter presenter domain model
79. class SpeakersListPresenter(val speakers: GetSpeakers, val coroutineContext: CoroutineContext) { lateinit var view: ISpeakersData fun attachView(currView: ISpeakersData) { view = currView fetchSpeakersList() } … presenter multiplatform network database android parser view platform specific presenter presenter domain model src/commonMain/presentation/SpeakersListPresenter.kt
80. class SpeakersListPresenter(val speakers: GetSpeakers, val coroutineContext: CoroutineContext) { lateinit var view: ISpeakersData fun attachView(currView: ISpeakersData) { view = currView fetchSpeakersList() } … presenter multiplatform network database android parser view platform specific presenter presenter domain model src/commonMain/presentation/SpeakersListPresenter.kt onCreate()/ viewDidLoad()
81. class SpeakersListPresenter(val speakers: GetSpeakers, val coroutineContext: CoroutineContext) { lateinit var view: ISpeakersData fun attachView(currView: ISpeakersData) { view = currView fetchSpeakersList() } … presenter multiplatform network database android parser view platform specific presenter presenter domain model src/commonMain/presentation/SpeakersListPresenter.kt
82. presenter multiplatform network database android parser view platform specific presenter presenter domain model src/commonMain/presentation/cb/ISpeakersData.kt interface ISpeakersData { fun onSpeakersDataFetched(speakers: List<Speaker>) fun onSpeakersDataFailed(e: Exception) }
83. class SpeakersListPresenter(val speakers: GetSpeakers, val coroutineContext: CoroutineContext) { lateinit var view: ISpeakersData fun attachView(currView: ISpeakersData) { view = currView fetchSpeakersList() } private fun fetchSpeakersList() { PresenterCoroutineScope(coroutineContext).launch { speakers( onSuccess = { view?.onSpeakersDataFetched(it) }, onFailure = { view?.onSpeakersDataFailed(it) }) … presenter multiplatform network database android parser view platform specific presenter presenter domain model src/commonMain/presentation/SpeakersListPresenter.kt
84. class SpeakersListPresenter(val speakers: GetSpeakers, val coroutineContext: CoroutineContext) { lateinit var view: ISpeakersData fun attachView(currView: ISpeakersData) { view = currView fetchSpeakersList() } private fun fetchSpeakersList() { PresenterCoroutineScope(coroutineContext).launch { speakers( onSuccess = { view?.onSpeakersDataFetched(it) }, onFailure = { view?.onSpeakersDataFailed(it) }) … presenter multiplatform network database android parser view platform specific presenter presenter domain model src/commonMain/presentation/SpeakersListPresenter.kt
85. object ServiceLocator { private val sessionizeAPI by lazy { SessionizeAPI(PlatformServiceLocator.httpClientEngine) } private val getSpeakers: GetSpeakers get() = GetSpeakers(sessionizeAPI, speakerDao) private val speakerDao by lazy { SpeakerDao(PlatformServiceLocator.databaseEngine) } val getSpeakersPresenter: SpeakersListPresenter get() = SpeakersPresenter(getSpeakers) … presenter multiplatform network database android parser view platform specific presenter presenter domain model src/commonMain/ServiceLocator.kt
87. platform specific expect object PlatformServiceLocator { val httpClientEngine: HttpClientEngine val databaseEngine: ScheduleDb } multiplatform network database android parser view platform specific presenter presenter domain model src/commonMain/PlatformServiceLocator.kt
88. platform specific expect object PlatformServiceLocator { val httpClientEngine: HttpClientEngine val databaseEngine: ScheduleDb } multiplatform network database android parser view platform specific presenter presenter domain model src/commonMain/PlatformServiceLocator.kt
89. actual object PlatformServiceLocator { actual val httpClientEngine: HttpClientEngine by lazy { OkHttp.create() } actual val databaseEngine: SqlDriver by lazy { AndroidSqliteDriver(ScheduleDb.Schema, context, "droidcon.db") … platform specific androidMain iOSMain multiplatform network database android parser view platform specific presenter presenter domain model
90. actual object PlatformServiceLocator { actual val httpClientEngine: HttpClientEngine by lazy { OkHttp.create() } actual val databaseEngine: SqlDriver by lazy { AndroidSqliteDriver(ScheduleDb.Schema, context, "droidcon.db") … platform specific androidMain actual object PlatformServiceLocator { actual val httpClientEngine: HttpClientEngine by lazy { Ios.create() } actual val databaseEngine: SqlDriver by lazy { NativeSqliteDriver(ScheduleDb.Schema, "droidcon.db") … iOSMain multiplatform network database android parser view platform specific presenter presenter domain model
91. actual object PlatformServiceLocator { actual val httpClientEngine: HttpClientEngine by lazy { OkHttp.create() } actual val databaseEngine: SqlDriver by lazy { AndroidSqliteDriver(ScheduleDb.Schema, context, "droidcon.db") … platform specific androidMain actual object PlatformServiceLocator { actual val httpClientEngine: HttpClientEngine by lazy { Ios.create() } actual val databaseEngine: SqlDriver by lazy { NativeSqliteDriver(ScheduleDb.Schema, "droidcon.db") … iOSMain multiplatform network database android parser view platform specific presenter presenter domain model
92. src/commonAndroid/presenter/activities/MainActivity.kt android class MainActivity : AppCompatActivity(), ISpeakersData { val presenter by lazy { ServiceLocator.getSpeakersPresenter } override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) presenter.attachView(this) } override fun onSpeakersDataFetched(list: List<Speaker>){ setup(list) … multiplatform network database android parser view platform specific presenter presenter domain model
93. src/commonAndroid/presenter/activities/MainActivity.kt android class MainActivity : AppCompatActivity(), ISpeakersData { val presenter by lazy { ServiceLocator.getSpeakersPresenter } override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) presenter.attachView(this) } override fun onSpeakersDataFetched(list: List<Speaker>){ setup(list) … multiplatform network database android parser view platform specific presenter presenter domain model
94. src/commonAndroid/presenter/adapters/SpeakersListAdapter.kt android multiplatform network database android parser view platform specific presenter presenter domain model override fun onBindViewHolder(viewHolder: SpeakerViewHolder, position: Int) { val speaker = speakers[position] Glide.with(viewHolder.speakerPhoto) .load(speaker.profilePicture) .apply(RequestOptions.circleCropTransform()) .into(viewHolder.speakerPhoto) viewHolder.speakerName.text = speaker.fullName viewHolder.talkTitle.text = speaker.talkTitle viewHolder.container.setOnClickListener { action.onUserClickAction(speaker, it) } }
95. src/commonAndroid/presenter/adapters/SpeakersListAdapter.kt android override fun onBindViewHolder(viewHolder: SpeakerViewHolder, position: Int) { val speaker = speakers[position] Glide.with(viewHolder.speakerPhoto) .load(speaker.profilePicture) .apply(RequestOptions.circleCropTransform()) .into(viewHolder.speakerPhoto) viewHolder.speakerName.text = speaker.fullName viewHolder.talkTitle.text = speaker.talkTitle viewHolder.container.setOnClickListener { action.onUserClickAction(speaker, it) } } you can keep using your android libraries multiplatform network database android parser view platform specific presenter presenter domain model
96. iosApp/iosApp/SpeakerTableViewController.swift iOS multiplatform network database iOS parser view platform specific presenter presenter domain model class SpeakerTableViewController: UITableViewController, ISpeakersData lazy var presenter = ServiceLocator.init().getSpeakerPresenter override func viewWillAppear(_ animated: Bool) { super.viewWillAppear(animated) presenter.attachView(view: self) } func onSpeakersDataFetched(speakers: [Speaker]) { setup(speakers) …
97. iosApp/iosApp/SpeakerTableViewController.swift iOS multiplatform network database iOS parser view platform specific presenter presenter domain model class SpeakerTableViewController: UITableViewController, ISpeakersData { lazy var presenter = ServiceLocator.init().getSpeakersPresenter override func viewWillAppear(_ animated: Bool) { super.viewWillAppear(animated) presenter.attachView(view: self) } func onSpeakersDataFetched(speakers: [Speaker]) { setup(speakers) …
98. iosApp/iosApp/SpeakerTableViewController.swift iOS multiplatform network database iOS parser view platform specific presenter presenter domain model override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell { let cellIdentifier = "SpeakerTableViewCell" let cell = tableView.dequeueReusableCell(withIdentifier: cellIdentifier, for: indexPath) as SpeakerTableViewCell let speaker = speakers[indexPath.row] cell.talkName.text = speaker.talkTitle cell.speakerName.text = speaker.fullName cell.speakerImage.image = speaker.profilePicture return cell }
99. conclusions don’t forget to bring your own towel.
100. team structure Kotlin Multiplatform android iOS
101. team structure Kotlin Multiplatform android iOS mobile backend documentation tests clean API
102. (impressions) Kotlin Multiplatform I could just focus on doing what I know best - UI. I have no idea how things are being done in the backend, yet I know that when I ask for data I receive it. - iOS Developer
103. - it’s in experimental state - although there are projects in production - you can spend some time resolving compilation issues - specially if you try to target all platforms - not possible to debug kotlin from Xcode - there’s a plugin for Xcode from TouchLab - lookout for plugins/ libraries updates (in progress) Kotlin Multiplatform
104. - strong community - a lot of people are using kotlin nowadays - Google and JetBrains are pushing Kotlin in - you can ask questions directly on https://kotlinlang.slack.com - 2x faster to develop your features business logic - 2x faster writing unit tests - one tech stack - consistency across platforms (conclusions) Kotlin Multiplatform
105. - be extremely careful with all updates - IDEA, jdk, kotlin, libraries - everything. - start small, don’t try to reach 100% of shared logic - keep versioning in mind - remember that’s still on experimental state (suggestions) Kotlin Multiplatform
106. - Kotlin Slack - Android @ Portugal Slack - Kotlin Official - Kotlin Training - Kotlin by: https://jakewharton.com/presentations/ http://antonioleiva.com/kotlin (useful links) more information
107. @cafonsomota so long and thanks for all the fish