Challenges of Building Kotlin Multiplatform Libraries

1. Mohit Sarveiya Building Kotlin Multiplatform Libraries @heyitsmohit
2. Building Kotlin Multiplatform Libraries • Setting up KMM project • CI Challenges • API Design Challenges
3. Why Kotlin Multiplatform? Android Kotlin/JVM iOS Swift/LLVM Web JS
4. Why Kotlin Multiplatform? API API API
5. Why Kotlin Multiplatform? Retrofit Ajax Alamofire
6. Why Kotlin Multiplatform? Room/SQL Delight Core Data
7. Why Kotlin Multiplatform? Business Logic Business Logic Business Logic
8. Why Kotlin Multiplatform? MVP/MVVM/MVI ReactJs VIPER
9. Why Kotlin Multiplatform? Shared code
10. Why Kotlin Multiplatform? API Business Logic Analytics Cache
11. Setting up KMM Project
12. Use Case Show platform name Hello 
 Android
13. Hello 
 iOS Use Case 9:41 Show platform name
14. Greeter Use Case
15. How to create Multiplatform app
16. Plugin https: // plugins.jetbrains.com/plugin/14936-kotlin-multiplatform-mobile
17. Project Setup Shared
18. Project Setup Shared Android App
19. Project Setup Shared Android App iOS App XCode Project
20. Project Setup Shared Android App iOS App
21. Project Setup Shared Android App iOS App Framework
22. Project Setup Shared Android App iOS App
23. Shared Module Structure
24. Shared Module Shared src commonMain
25. Shared Module Shared src commonMain androidMain
26. Shared Module Shared src commonMain androidMain iOSMain
27. Greeter Use Case
28. Common Shared Module Android iOS Platform name
29. Common expect class Platform() { val platform: String }
30. Common expect class Platform() { val platform: String }
31. Common expect class Platform() { val platform: String }
32. Common expect class Platform() { val platform: String } Common
33. Common Android Android iOS Platform name
34. Android actual class Platform actual constructor() { actual val platform: String = ”Android” }
35. Android actual class Platform actual constructor() { actual val platform: String = ”Android” }
36. Android actual class Platform actual constructor() { actual val platform: String = ”Android” }
37. Android actual class Platform actual constructor() { actual val platform: String = ”Android” } Common Android
38. Common iOS Android iOS Platform name
39. iOS actual class Platform actual constructor() { actual val platform: String = “iOS” }
40. Common Shared Module Android iOS Platform name
41. Common class Greeter { fun greet(): String { return "Hello ${Platform().platform}!" } }
42. Common class Greeter { fun greet(): String { return "Hello ${Platform().platform}!" } }
43. Using Shared Module
44. Project Setup Shared Android App iOS App
45. Use Case Show platform name Hello 
 Android
46. Android App class MainActivity : AppCompatActivity() { }
47. Android App class MainActivity : AppCompatActivity() { fun onCreate( ... ) { val greeting = Greeter().greet() } }
48. Android App class MainActivity : AppCompatActivity() { fun onCreate( ... ) { val greeting = Greeter().greet() textView.text = greeting } }
49. Android App class Greeter { ... } Common Source Build
50. Use Case Hello 
 Android
51. Android App class MainActivity : AppCompatActivity() { fun onCreate( ... ) { val greeting = Greeter().greet() textView.text = greeting } }
52. Hello 
 iOS Use Case 9:41 Show platform name
53. iOS App class Greeter { ... } Common Source Build Framework
54. iOS App import SwiftUI import shared
55. iOS App import SwiftUI import shared func greet() -> String { return Greeting().greeting() }
56. iOS App import SwiftUI import shared struct ContentView: View { var body: some View { } }
57. iOS App import SwiftUI import shared struct ContentView: View { var body: some View { Text(greet()) } }
58. Hello 
 iOS Use Case 9:41 Show platform name
59. Inside Objective-C Framework
60. iOS Framework class Greeter { ... } Common Source Build Framework
61. iOS Framework import SwiftUI import shared func greet() -> String { return Greeting().greeting() }
62. iOS Framework Shared Base Shared Platform Shared Greeting
63. Shared Base __attribute__((swift_name("KotlinBase"))) @interface SharedBase : NSObject ... @end;
64. Shared Base __attribute__((swift_name("KotlinBase"))) @interface SharedBase : NSObject ... @end;
65. iOS actual class Platform actual constructor() { actual val platform: String = “iOS” }
66. Mappings https: // kotlinlang.org/docs/native-objc-interop.html#mappings
67. Shared Platform __ attribute __ ((swift_name(“Platform"))) @interface SharedPlatform : SharedBase ... @end;
68. Shared Platform __ attribute __ ((swift_name(“Platform"))) @interface SharedPlatform : SharedBase @property (readonly) NSString *platform 
 @end;
69. Common class Greeter { fun greet(): String { return "Hello ${Platform().platform}!" } }
70. Common @interface SharedGreeting : SharedBase - (NSString *)greeting __ attribute __ ((swift_name("greeting()"))); @end;
71. Android & iOS Shared Modules
72. Use Case Hello 
 Android 29
73. Shared Module Shared src commonMain androidMain iOSMain
74. Android actual class Platform actual constructor() { actual val platform: String = 
 “Android ${android.os.Build.VERSION.SDK_INT}" }
75. Hello 
 iOS 14.4 Use Case 9:41
76. Shared Module Shared src commonMain androidMain iOSMain
77. iOS import platform.UIKit.UIDevice actual class Platform actual constructor() { actual val platform: String = UIDevice.currentDevice.systemName() + " " + 
 UIDevice.currentDevice.systemVersion }
78. iOS import platform.UIKit.UIDevice actual class Platform actual constructor() { actual val platform: String = UIDevice.currentDevice.systemName() + " " + 
 UIDevice.currentDevice.systemVersion }
79. Summary • How to build KMM project • Shared Module Setup • Inside Shared Framework
80. CI Challenges
81. Swift Package Manager
82. Framework KMM Library
83. Swift Package Manager KMM Library
84. Multiplatform Swift Package • Gradle plugin • Generate XCFramework
85. Multiplatform Swift Package id("com.chromaticnoise.multiplatform-swiftpackage") version "2.0.3"
86. Multiplatform Swift Package multiplatformSwiftPackage { swiftToolsVersion(“5.5") targetPlatforms { iOS { v("13") } } }
87. Multiplatform Swift Package ./gradlew createSwiftPackage
88. KMM Library XCEFramework
89. Projects/KMMProject Code ! Issues Pull Requests KMMLibrary.xcframework 1 commit 4c28f942 13 hours ago Package.swift KMMLibrary-1.0.zip README.md
90. Choose Package Repository Search or enter package repository URL Name Last Updated Owner Projects(Github) KMMPackage Today 13:00 user
91. Add Package to Project Choose package and targets Kind Add to Target KMMLibrary Library TestKMMLibrary Package Product
92. Steps • Create XCEFramework • Consume using Swift Package Manager
93. Build Automation
94. KMM Library bdae142 .. main 50157a .. d89f145 .. f0ddfb ..
95. bdae142 .. main 50157a .. d89f145 .. f0ddfb ..
96. KMM Library Jar XCEFramework
97. KMM Library Jar XCEFramework Artifactory
98. Artifactory
99. Build Automation • Setup CI to create artifcats • Use artifacts from repository like Artifactory
100. API Design Challenges
101. Flows
102. Common fun getData(): Flow<Data>
103. Android val flow = getData() flow.collect { }
104. iOS getData( collector: T ## Kotlinx_coroutines_coreFlowCollector, completionHandler: (KotlinUnit?, Error?) -> Void )
105. Common class CFlow internal constructor( val origin: Flow ) : Flow by origin { fun watch(block: (T) -> Unit) { } }
106. Common class CFlow internal constructor( val origin: Flow ) : Flow by origin { fun watch(block: (T) -> Unit) { onEach { block(it) } launchIn(CoroutineScope( ... )) } }
107. Common fun Flow<T>.wrap(): CFlow<T> = CFlow(this)
108. iOS flow .wrap() .watch { data ->
 }
109. Building Kotlin Multiplatform Libraries • Setting up KMM project • CI Challenges • API Design Challenges
110. Thank You! www.codingwithmohit.com @heyitsmohit