Kotlin Multiplatform

Introduction to Kotlin Multiplatform that I gave at Kotlin Everywhere in Minneapolis on October 5, 2019

Transcript

1. Kotlin Multiplatform Bryan Herbst
2. Beware: Kotlin MPP is under development
3. Why cross-platform?
10. More platforms = More developers More money More code More bugs
11. More platforms = More developers More money More code More bugs
12. More platforms = More developers More money More code More bugs
13. More platforms = More developers More money More code More bugs
14. Fewer platforms = Fewer developers? Less money? Less code? Fewer bugs?
15. User Experience is table stakes
16. User Experience is table stakes How native is the UI? How responsive is the app?
17. User Experience is table stakes How native is the UI? How responsive is the app?
18. Developer happiness is critical
19. Developer happiness is critical Speed of platform updates Interop with native Interop with existing code Language
20. Developer happiness is critical Speed of platform updates Interop with native Interop with existing code Language
21. Developer happiness is critical Speed of platform updates Interop with native Interop with existing code Language
22. Developer happiness is critical Speed of platform updates Interop with native Interop with existing code Language
23. Cross-platform architecture
24. What to share?
25. As much (or as little) as you want
26. Embrace platform differences, but provide a consistent core
27. Assumption: you already have an iOS & Android app
28. Feature UI Logic Data
29. Feature UI Logic Data Data models, Networking
30. Feature UI Logic Data Great place to start!
31. Feature UI Logic Data ViewControllers, ViewModels
32. Feature UI Logic Data Trickier
33. Feature UI Logic Data Layouts, Views
34. Feature UI Logic Data Probably not worth it
35. What is platform dependent?
36. What is platform dependent? Almost everything the user sees
37. What is platform dependent? Logging
38. What is platform dependent? Disk storage
39. What is platform dependent? Networking
40. Shared Library Common Android iOS
41. Shared Library Common Android iOS Android App iOS App
42. Shared Library Common Android iOS Android App iOS App lib lib
43. Mono Repo Common Android iOS Android App iOS App lib lib
44. Shared Library Common Android iOS Android App iOS App lib lib
45. How Kotlin MPP works
46. kotlinc Main.kt
47. kotlinc Frontend Intermediate representation Backend
48. kotlinc Frontend Intermediate representation Backend
49. kotlinc Frontend Intermediate representation Backend
50. kotlinc Frontend Intermediate representation Kotlin JVM
51. kotlinc Frontend Intermediate representation Kotlin JS
52. kotlinc Frontend Intermediate representation Kotlin Native
53. Kotlin JVM Output is bytecode
54. Kotlin JVM 100% interoperability
55. Kotlin JS Output is JS
56. Kotlin JS Output is JS
57. Kotlin JS - libraries Dukat binds strongly-typed libraries
58. Kotlin JS - libraries dynamic type supports loose typing
59. Dynamic val dyn: dynamic = ...
60. Dynamic Disables type checking
61. Dynamic Can call any property or function
62. Kotlin Native Outputs native binary
63. Kotlin Native Outputs native binary Executable
64. Kotlin Native Outputs native binary Executable C library
65. Kotlin Native Outputs native binary Executable C library Apple framework
66. Kotlin Native Compiled with LLVM
67. Kotlin Native arm32, arm64 x86, x86_64 mingw x86_64 MIPS, rPi wasm32
68. Native libraries 1. Create .def 2. Cinterop creates kotlin bindings of C/C++ code
69. Native libraries 1. Create .def 2. cinterop produces Kotlin bindings
70. Native libraries Platform libraries
71. Native libraries Platform libraries e.g. Open GL, objc, posix
72. Swift?
73. Kotlin Multiplatform
74. Main.kt Frontend IR JVM Native JS
75. Let’s get started!
76. plugins { id 'org.jetbrains.kotlin.multiplatform' version '1.3.50’ }
77. kotlin { jvm() // Creates a JVM target }
78. kotlin { iosArm32("ios32") iosArm64("ios64") configure([ios32, ios64]) { binaries.framework { baseName = "SharedCode" } } }
79. kotlin { iosArm32("ios32") iosArm64("ios64") configure([ios32, ios64]) { binaries.framework { baseName = "SharedCode" } } }
80. kotlin { iosArm32("ios32") iosArm64("ios64") // Simulator iosX64("iosX64") }
81. val sdk = System.getenv("SDK_NAME") if (sdk?.startsWith("iphoneos")) { iosX64("iosX64") } else { //.... }
82. Carthage or CocoaPods
83. plugins { id("org.jetbrains.kotlin.native.cocoapods") } kotlin { cocoapods { summary = "Shared library" homepage = "http://github.com/shared-lib" } }
84. Time to write some code
85. Android Notes UI NotesView Model Note (model) Note API iOS Notes UI NotesView Controller Note (model) Note API
86. Android Notes UI NotesView Model Note API iOS Notes UI NotesView Controller Note API Shared Note (model)
87. Note JSON { content: "Hello", status: "Pinned" }
88. iOS struct Note { let content: String let status: String } Android data class Note( val content: String, val status: Status ) enum class Status { }
89. iOS struct Note { let content: String let status: String } Android data class Note( val content: String, val status: Status ) enum class Status { }
90. iOS struct Note { let content: String let status: String } Android data class Note( val content: String, val status: Status ) enum class Status { }
91. data class Note( val content: String, val status: String ) Shared
92. data class Note( val content: String, val status: String ) Android
93. __attribute__((objc_subclassing_restricted)) __attribute__((swift_name("Note"))) @interface SharedNote : KotlinBase @property (readonly) NSString * content; @property (readonly) NSString * status; @end; iOS
94. __attribute__((objc_subclassing_restricted)) __attribute__((swift_name("Note"))) @interface SharedNote : KotlinBase @property (readonly) NSString * content; @property (readonly) NSString * status; @end; iOS
95. __attribute__((objc_subclassing_restricted)) __attribute__((swift_name("Note"))) @interface SharedNote : KotlinBase @property (readonly) NSString * content; @property (readonly) NSString * status; @end; iOS – Objective C
96. class Note: KotlinBase { private(set) var content: String? private(set) var status: String? } iOS – Swift
97. Android Notes UI NotesView Model Note API iOS Notes UI NotesView Controller Note API Shared Note (model)
98. Android Notes UI NotesView Model iOS Notes UI NotesView Controller Shared Note (model) Note API
99. Serialization Kotlinx.serialization
100. @Serializable data class Note( val content: String val status: String )
101. Json.nonstrict .stringify( Note.serializer(), note )
102. Json.nonstrict .parse( Note.serializer(), jsonString )
103. Json.nonstrict .parse( Note.serializer().list, jsonString )
104. Serialization is multiplatform!
105. Serialization is multiplatform! Charsets, input streams, buffers
106. commonMain { dependencies { implementation "serialization-runtime-common" } }
107. jvmMain { dependencies { implementation "serialization-runtime" } }
108. nativeMain { dependencies { implementation "serialization-runtime-native" } }
109. Networking KTOR
110. Under the hood - engines Android: OkHttp, HttpUrlConnection
111. Under the hood - engines Android: OkHttp, HttpUrlConnection iOS: NSUrlSession
112. class NoteApi() { private val client = HttpClient() suspend fun fetchNote(): String = client.get<String>("http://...") }
113. How do we support different platforms?
114. common/PlatformName.kt expect fun getPlatform(): String
115. android/PlatformName.kt actual fun getPlatform()= "Android"
116. ios/PlatformName.kt actual fun getPlatform() = "iOS"
117. Common/KeyValueStore.kt expect class KeyValueStore() { fun setString(key: String, value: String) fun getString(key: String): String }
118. android/KeyValueStore.kt actual class KeyValueStore() { private val prefs: SharedPreferences actual fun setString() //... actual fun getString() //... }
119. ios/KeyValueStore.kt actual class KeyValueStore() { private val userDefaults: NSUserDefaults actual fun setString() //... actual fun getString() //... }
120. expect interface Closeable { fun close() } actual typealias Closeable = java.io.Closeable
121. Platform differences
123. Unsupported in Swift/Obj-C Suspend functions Inline classes
124. Asyncronous work
125. Coroutines Only single-threaded code is currently supported for Kotlin/Native
126. Exceptions
127. Exceptions All Kotlin exceptions are unchecked
128. Exceptions All Kotlin exceptions are unchecked Swift only has checked errors
129. Exceptions Annotate with @Throws
130. Primitive types Int -> KotlinInt
131. Primitive types Int -> KotlinInt (NSNumber)
132. Generics
133. Generics Experimental for Kotlin Native
134. Generics Experimental for Kotlin Native extraOpts "-Xobjc-generics"
135. Kotlin: class Generic<T> Swift: class Generic<T>
136. Kotlin: class Generic<T> Swift: class Generic<T>
137. Kotlin: class Generic<T>(val item: T) Swift: class Generic<T> { let item: T? }
138. Kotlin: class Generic<T>(val item: T) Swift: class Generic<T> { let item: T? } ?
139. Kotlin: class Generic<T: Any>(val item: T) Swift: class Generic<T> { let item: T }
140. Thanks!