Expecting fun with Kotlin Multiplatform Mobile

This talk aims to introduce the Kotlin Multiplatform concept, with its advantages and disadvantages, and how this concept is different from cross-platform solutions in code reuse between platforms. Finally, the application of this concept will be shown in a simple chat made with kotlin for Android and iOS.

References:
- https://kotlinlang.org/lp/mobile/
- https://github.com/felipehjcosta/chat-app

Delivered in the following events

- TDC 2020 Porto Alegre, December 2 to 4, 2020

1. Expecting fun with Kotlin Multiplatform Mobile
2. Felipe Costa Software engineering manager @ OLX Brasil Software professional passionate about mobile and open source technologies with over 10 years of experience as a software engineer. Kotlin enthusiast since 2016.
3. Our purpose We approach Brazilians to turn items into happiness.
4. Kotlin @ OLX 0 Python Javascript Java C PHP Kotlin Objective-C Perl
5. Kotlin @ OLX 0 Android Authentication Experimentação Insertion Search Recomendation
6. Kotlin History
7. 2011 Jetbrains unveiled Project Kotlin 2012 Jetbrains open sourced the project 2015 Using Project Kotlin for Android (Square) 2016 Kotlin 1.0 (first officially stable release) 2017 First-class support for Kotlin on Android
8. 2017 Kotlin 1.2 (Kotlin Multiplatform) 2018 Kotlin 1.3 (coroutines) 2019 Preferred language for Android app developers 2020 Kotlin 1.4 (support for Apple's platforms) 2020 Kotlin Multiplatform Mobile Goes Alpha
9. Why Kotlin Multiplatform Mobile (KMM)?
10. Optional Sharing Low risk No Big decisions
11. 100% Native smooth interop First class citizen
12. Code sharing not “cross platform”
13. Activity community
14. Good tools
15. Modern Language
16. Not necessarily UI Business rules
17. Who uses KMM
22. Evaluating other solutions
23. Input Process Output App type Native Language: Kotlin & Swift & JS Outra linguagem Cross-Compile Inclui Runtime (Interpretador, VM, Bibliotecas) Native Code Native Language: Javascript Native Web Native Web
24. Input Process Output App type Native Language Other Language: Javascript Cross-Compile Include Runtime (Interpreter, VM, Libraries) Native Code + Bundle JS Native Language Native Web React Native
25. Flutter Input Process Output App type Native Language Other Language: Dart Cross-Compile Include Runtime (Interpreter, VM, Libraries) Native Code Native Language Native Web
26. Kotlin Multiplatform Input Process Output App Type Native Language: Kotlin Other Language Cross-Compile Include Runtime (Interpreter, VM, Libraries) Native Code Native Language: Javascript Native Web Android iOS Web
27. Architecture
28. Architecture
29. Multiplaform code
30. Common *.kt
31. plugins { id 'kotlin-multiplatform' version ‘1.4.0' } repositories { mavenCentral() } kotlin { sourceSets { commonMain { dependencies { implementation “io.ktor:ktor-client-core:1.4.0” } } } } Build.gradle
32. plugins { id 'kotlin-multiplatform' version ‘1.4.0' } repositories { mavenCentral() } kotlin { sourceSets { commonMain { dependencies { implementation "io.ktor:ktor-client-core:1.4.0" } } } } Build.gradle
33. plugins { id 'kotlin-multiplatform' version '1.4.0' } repositories { mavenCentral() } kotlin { sourceSets { commonMain { dependencies { implementation “io.ktor:ktor-client-core:1.4.0” } } } } Build.gradle
34. plugins { id 'kotlin-multiplatform' version '1.4.0' } repositories { mavenCentral() } kotlin { sourceSets { commonMain { dependencies { implementation “io.ktor:ktor-client-core:1.4.0” } } } } Build.gradle
35. Common *.kt
36. Common *.kt *.class *.jar, *.apk
37. kotlin { android() sourceSets { commonMain { /* */ } } } Build.gradle
38. kotlin { android() sourceSets { commonMain { /* */ } } } Build.gradle
39. kotlin { android() sourceSets { commonMain { /* */ } } } Build.gradle
40. Common *.kt *.class *.jar, *.apk binário nativo iOS Watch
41. kotlin { android() iosArm64 { binaries { framework(“shared”) } } sourceSets { commonMain { /* */ } } } Build.gradle
42. kotlin { android() iosArm64 { binaries { framework(“shared”) } } sourceSets { commonMain { /* */ } } } Build.gradle
43. kotlin { android() iosArm64 { binaries { framework(“shared”) } } sourceSets { commonMain { /* */ } } } Build.gradle
44. fun hello(): String = "Hello from Kotlin Multiplatform" Common
45. import kotlin.Metadata; import org.jetbrains.annotations.NotNull; @Metadata( mv = {1, 1, 15}, bv = {1, 0, 3}, k = 2, d1 = {"\u0000\b\n\u0000\n\u0002\u0010\u000e\n\u0000\u001a\u0006\u0010\u0000\u001a\u00020\u0001¨\u0006\u0002"}, d2 = {"hello", "", "Platform module com.example.hello-world-multiplatform.jvmMain including [com.example.hello-world-multiplatform.commonMain]"} ) public final class SampleKt { @NotNull public static final String hello() { return "Hello from Kotlin Multiplatform"; } } Android
46. iOS Framework #import <Foundation/Foundation.h> NS_ASSUME_NONNULL_BEGIN @interface KotlinBase : NSObject - (instancetype)init __attribute__((unavailable)); + (instancetype)new __attribute__((unavailable)); + (void)initialize __attribute__((objc_requires_super)); @end; @interface KotlinBase (KotlinBaseCopying) <NSCopying> @end; /* More types */ __attribute__((objc_subclassing_restricted)) __attribute__((swift_name("SampleKt"))) @interface FrameworkSampleKt : KotlinBase + (NSString *)hello __attribute__((swift_name("hello()"))); @end; NS_ASSUME_NONNULL_END
47. Platform-specific code
48. fun hello(): String = "Hello from Kotlin Multiplatform" Common
49. object Platform { val name: String } fun hello(): String = "Hello from ${Platform.name}" Common
50. object Platform { val name: String = “Android" } fun hello(): String = "Hello from ${Platform.name}" Android
51. object Platform { val name: String = “iOS" } fun hello(): String = "Hello from ${Platform.name}" iOS
52. Common *.kt *.class *.jar, *.apk native binary iOS Watch
53. Common *.kt Kotlin/JVM *.kt, *.java Kotlin/Native *.kt, *.c *.class *.jar, *.apk native binary iOS Watch
54. Expect/Actual
55. expect object Platform { val name: String } fun hello(): String = "Hello from ${Platform.name}" Common
56. expect object Platform { val name: String } fun hello(): String = "Hello from ${Platform.name}" Common
57. expect object Platform { val name: String } fun hello(): String = "Hello from ${Platform.name}" Common
58. kotlin { android() iosArm64 { binaries { framework(“shared”) } } sourceSets { commonMain { /* */ } androidMain { dependencies { /* */ } } } } build.gradle
59. kotlin { android() iosArm64 { binaries { framework(“shared”) } } sourceSets { commonMain { /* */ } androidMain { dependencies { /* */ } } } } build.gradle
60. kotlin { android() iosArm64 { binaries { framework(“shared”) } } sourceSets { commonMain { /* */ } androidMain { dependencies { /* */ } } } } build.gradle
61. actual object Platform { actual val name: String = "Android" } fun hello(): String = "Hello from Android” Android
62. actual object Platform { actual val name: String = "Android" } fun hello(): String = "Hello from Android” Android
63. actual object Platform { actual val name: String = "Android" } fun hello(): String = "Hello from Android” Android
64. kotlin { android() iosArm64 { binaries { framework(“shared”) } } sourceSets { commonMain { /* */ } androidMain { /* */ } iosArm64Main { } } } build.gradle
65. kotlin { android() iosArm64 { binaries { framework(“shared”) } } sourceSets { commonMain { /* */ } androidMain { /* */ } iosArm64Main { } } } build.gradle
66. kotlin { android() iosArm64 { binaries { framework(“shared”) } } sourceSets { commonMain { /* */ } androidMain { /* */ } iosArm64Main { } } } build.gradle
67. actual object Platform { actual val name: String = "iOS" } fun hello(): String = "Hello from iOS” iOS
68. actual object Platform { actual val name: String = "iOS" } fun hello(): String = "Hello from iOS” iOS
69. actual object Platform { actual val name: String = "iOS" } fun hello(): String = "Hello from iOS” iOS
70. Tests?
71. kotlin { android() iosArm64 { binaries { framework(“shared”) } } sourceSets { commonMain { /* */ } commonTest { /* */ } androidMain { /* */ } androidTest { /* */ } iosArm64Main { /* */ } iosArm64Test { /* */ } } } build.gradle
72. kotlin { android() iosArm64 { binaries { framework(“shared”) } } sourceSets { commonMain { /* */ } commonTest { /* */ } androidMain { /* */ } androidTest { /* */ } iosArm64Main { /* */ } iosArm64Test { /* */ } } } build.gradle
73. kotlin { android() iosArm64 { binaries { framework(“shared”) } } sourceSets { commonMain { /* */ } commonTest { /* */ } androidMain { /* */ } androidTest { /* */ } iosArm64Main { /* */ } iosArm64Test { /* */ } } } build.gradle
74. kotlin { /* */ sourceSets { /* */ commonTest { dependencies { implementation kotlin('test-common') implementation kotlin('test-annotations-common') } } androidTest { dependencies { implementation kotlin('test') implementation kotlin('test-junit') } } iosArm64Test { } } } build.gradle
75. import kotlin.test.Test import kotlin.test.assertTrue class SampleTestsAndroid { @Test fun testHello() { assertTrue(“Android" in hello()) } } Android
76. import kotlin.test.Test import kotlin.test.assertTrue class SampleTestsIOS { @Test fun testHello() { assertTrue(“iOS" in hello()) } } iOS
77. expect class Sample() { fun checkMe(): Int } object Platform { val name: String } fun hello(): String = "Hello from ${Platform.name}" Common
78. import kotlin.test.Test import kotlin.test.assertTrue class SampleTests { @Test fun testMe() { assertTrue(Sample().checkMe() > 0) } } Common
79. Libraries
80. Ktor Kotlinx.Coroutines kotlinx.io kotlinx.serialization sqldelight MPSettings Stately KorLibs kotlinx-datetime Decompose (UI State)
82. Multiplatform Chat
83. Architecture Common Client Android iOS Server
84. Architecture Android iOS Server Main Common Message Client ChatViewModel PlatformSocket
85. Common PlatformSocket.kt Kotlin/JVM PlatformSocket.kt Kotlin/Native PlatformSocket.kt *.class *.jar, *.apk native binary iOS Watch
86. expect class PlatformSocket(url: String) { fun openSocket(listener: PlatformSocketListener) fun closeSocket(code: Int, reason: String) fun sendMessage(msg: String) } interface PlatformSocketListener { fun onOpen() fun onFailure(t: Throwable) fun onMessage(msg: String) fun onClosing(code: Int, reason: String) fun onClosed(code: Int, reason: String) } Common
87. expect class PlatformSocket(url: String) { fun openSocket(listener: PlatformSocketListener) fun closeSocket(code: Int, reason: String) fun sendMessage(msg: String) } interface PlatformSocketListener { fun onOpen() fun onFailure(t: Throwable) fun onMessage(msg: String) fun onClosing(code: Int, reason: String) fun onClosed(code: Int, reason: String) } Common
88. expect class PlatformSocket(url: String) { fun openSocket(listener: PlatformSocketListener) fun closeSocket(code: Int, reason: String) fun sendMessage(msg: String) } interface PlatformSocketListener { fun onOpen() fun onFailure(t: Throwable) fun onMessage(msg: String) fun onClosing(code: Int, reason: String) fun onClosed(code: Int, reason: String) } Common
89. import okhttp3.OkHttpClient import okhttp3.Request import okhttp3.Response import okhttp3.WebSocket actual class PlatformSocket actual constructor(url: String) { private val socketEndpoint = url private var webSocket: WebSocket? = null actual fun openSocket(listener: PlatformSocketListener) { val socketRequest = Request.Builder().url(socketEndpoint).build() val webClient = OkHttpClient().newBuilder().build() webSocket = webClient.newWebSocket( socketRequest, object : okhttp3.WebSocketListener() { override fun onOpen(webSocket: WebSocket, response: Response) = listener.onOpen() override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) = listener.onFailure(t) override fun onMessage(webSocket: WebSocket, text: String) = listener.onMessage(text) override fun onClosing(webSocket: WebSocket, code: Int, reason: String) = listener.onClosing(code, reason) override fun onClosed(webSocket: WebSocket, code: Int, reason: String) = listener.onClosed(code, reason) } ) } actual fun closeSocket(code: Int, reason: String) { webSocket?.close(code, reason) webSocket = null } actual fun sendMessage(msg: String) { webSocket?.send(msg) } } Android
90. import okhttp3.OkHttpClient import okhttp3.Request import okhttp3.Response import okhttp3.WebSocket actual class PlatformSocket actual constructor(url: String) { private val socketEndpoint = url private var webSocket: WebSocket? = null actual fun openSocket(listener: PlatformSocketListener) { val socketRequest = Request.Builder().url(socketEndpoint).build() val webClient = OkHttpClient().newBuilder().build() webSocket = webClient.newWebSocket( socketRequest, object : okhttp3.WebSocketListener() { override fun onOpen(webSocket: WebSocket, response: Response) = listener.onOpen() override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) = listener.onFailure(t) override fun onMessage(webSocket: WebSocket, text: String) = listener.onMessage(text) override fun onClosing(webSocket: WebSocket, code: Int, reason: String) = listener.onClosing(code, reason) override fun onClosed(webSocket: WebSocket, code: Int, reason: String) = listener.onClosed(code, reason) } ) } actual fun closeSocket(code: Int, reason: String) { webSocket?.close(code, reason) webSocket = null } actual fun sendMessage(msg: String) { webSocket?.send(msg) } } Android
91. import okhttp3.OkHttpClient import okhttp3.Request import okhttp3.Response import okhttp3.WebSocket actual class PlatformSocket actual constructor(url: String) { private val socketEndpoint = url private var webSocket: WebSocket? = null actual fun openSocket(listener: PlatformSocketListener) { val socketRequest = Request.Builder().url(socketEndpoint).build() val webClient = OkHttpClient().newBuilder().build() webSocket = webClient.newWebSocket( socketRequest, object : okhttp3.WebSocketListener() { override fun onOpen(webSocket: WebSocket, response: Response) = listener.onOpen() override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) = listener.onFailure(t) override fun onMessage(webSocket: WebSocket, text: String) = listener.onMessage(text) override fun onClosing(webSocket: WebSocket, code: Int, reason: String) = listener.onClosing(code, reason) override fun onClosed(webSocket: WebSocket, code: Int, reason: String) = listener.onClosed(code, reason) } ) } actual fun closeSocket(code: Int, reason: String) { webSocket?.close(code, reason) webSocket = null } actual fun sendMessage(msg: String) { webSocket?.send(msg) } } Android
92. import platform.Foundation.* import platform.darwin.NSObject actual class PlatformSocket actual constructor(url: String) { private val socketEndpoint = NSURL.URLWithString(url)!! private var webSocket: NSURLSessionWebSocketTask? = null actual fun openSocket(listener: PlatformSocketListener) { val urlSession = NSURLSession.sessionWithConfiguration( configuration = NSURLSessionConfiguration.defaultSessionConfiguration(), delegate = object : NSObject(), NSURLSessionWebSocketDelegateProtocol { override fun URLSession(session: NSURLSession, webSocketTask: NSURLSessionWebSocketTask, didOpenWithProtocol: String?) { listener.onOpen() } override fun URLSession(session: NSURLSession, webSocketTask: NSURLSessionWebSocketTask, didCloseWithCode: NSURLSessionWebSocketCloseCode, reason: NSData?) { listener.onClosed(didCloseWithCode.toInt(), reason.toString()) } }, delegateQueue = NSOperationQueue.currentQueue() ) webSocket = urlSession.webSocketTaskWithURL(socketEndpoint) listenMessages(listener) webSocket?.resume() } private fun listenMessages(listener: PlatformSocketListener) { webSocket?.receiveMessageWithCompletionHandler { message, nsError -> when { nsError != null -> { listener.onFailure(Throwable(nsError.description)) } message != null -> { message.string?.let { listener.onMessage(it) } } } listenMessages(listener) } } actual fun closeSocket(code: Int, reason: String) { webSocket?.cancelWithCloseCode(code.toLong(), null) webSocket = null } actual fun sendMessage(msg: String) { val message = NSURLSessionWebSocketMessage(msg) webSocket?.sendMessage(message) { err -> err?.let { println("send $msg error: $it") } } } } iOS
93. import platform.Foundation.* import platform.darwin.NSObject actual class PlatformSocket actual constructor(url: String) { private val socketEndpoint = NSURL.URLWithString(url)!! private var webSocket: NSURLSessionWebSocketTask? = null actual fun openSocket(listener: PlatformSocketListener) { val urlSession = NSURLSession.sessionWithConfiguration( configuration = NSURLSessionConfiguration.defaultSessionConfiguration(), delegate = object : NSObject(), NSURLSessionWebSocketDelegateProtocol { override fun URLSession(session: NSURLSession, webSocketTask: NSURLSessionWebSocketTask, didOpenWithProtocol: String?) { listener.onOpen() } override fun URLSession(session: NSURLSession, webSocketTask: NSURLSessionWebSocketTask, didCloseWithCode: NSURLSessionWebSocketCloseCode, reason: NSData?) { listener.onClosed(didCloseWithCode.toInt(), reason.toString()) } }, delegateQueue = NSOperationQueue.currentQueue() ) webSocket = urlSession.webSocketTaskWithURL(socketEndpoint) listenMessages(listener) webSocket?.resume() } private fun listenMessages(listener: PlatformSocketListener) { webSocket?.receiveMessageWithCompletionHandler { message, nsError -> when { nsError != null -> { listener.onFailure(Throwable(nsError.description)) } message != null -> { message.string?.let { listener.onMessage(it) } } } listenMessages(listener) } } actual fun closeSocket(code: Int, reason: String) { webSocket?.cancelWithCloseCode(code.toLong(), null) webSocket = null } actual fun sendMessage(msg: String) { val message = NSURLSessionWebSocketMessage(msg) webSocket?.sendMessage(message) { err -> err?.let { println("send $msg error: $it") } } } } iOS
94. import platform.Foundation.* import platform.darwin.NSObject actual class PlatformSocket actual constructor(url: String) { private val socketEndpoint = NSURL.URLWithString(url)!! private var webSocket: NSURLSessionWebSocketTask? = null actual fun openSocket(listener: PlatformSocketListener) { val urlSession = NSURLSession.sessionWithConfiguration( configuration = NSURLSessionConfiguration.defaultSessionConfiguration(), delegate = object : NSObject(), NSURLSessionWebSocketDelegateProtocol { override fun URLSession(session: NSURLSession, webSocketTask: NSURLSessionWebSocketTask, didOpenWithProtocol: String?) { listener.onOpen() } override fun URLSession(session: NSURLSession, webSocketTask: NSURLSessionWebSocketTask, didCloseWithCode: NSURLSessionWebSocketCloseCode, reason: NSData?) { listener.onClosed(didCloseWithCode.toInt(), reason.toString()) } }, delegateQueue = NSOperationQueue.currentQueue() ) webSocket = urlSession.webSocketTaskWithURL(socketEndpoint) listenMessages(listener) webSocket?.resume() } private fun listenMessages(listener: PlatformSocketListener) { webSocket?.receiveMessageWithCompletionHandler { message, nsError -> when { nsError != null -> { listener.onFailure(Throwable(nsError.description)) } message != null -> { message.string?.let { listener.onMessage(it) } } } listenMessages(listener) } } actual fun closeSocket(code: Int, reason: String) { webSocket?.cancelWithCloseCode(code.toLong(), null) webSocket = null } actual fun sendMessage(msg: String) { val message = NSURLSessionWebSocketMessage(msg) webSocket?.sendMessage(message) { err -> err?.let { println("send $msg error: $it") } } } } iOS
95. Demo
97. Challenges
98. Alpha
99. Threads
101. Debug
103. Testing support
104. Compilation Time
105. Multiplatform UI
106. Compose
107. https://kotlinlang.org/lp/mobile/
109. felipehjcosta felipe.h.j.costa@gmail.com