The Triumphs and Tribulations of Kotlin/Native In Practice - Kotlin UserGroup Belgium, Brussels - March 2019

Now updated to be 100% more correct about why `runBlocking` doesn't work in a `common` framework without pretzeling yourself!

Abstract:
The promise of write-once-run-everywhere has haunted native mobile developers since the first time someone whispered the words “phone gap”. But what if there was a way to have cross-platform development with a modern, type-safe language? JetBrains is trying to make this happen with Kotlin/Native, which compiles to LLVM bytecode, and can run on iOS, Android, and even the web. Learn more about some of the benefits of working with Kotlin/Native, some of the drawbacks, and a few of the (current) potential dealbreakers when it comes to using this exciting new technology in a real app.

Links:
- Main Project: https://github.com/bakkenbaeck/PorchPirateProtector
- Initial K/N Test: https://github.com/designatednerd/KotlinNativeTest

Transcript

1. THE TRIUMPHS AND TRIBULATIONS OF KOTLIN/NATIVE IN PRACTICE KOTLIN USERGROUP BELGIUM | BRUSSELS | MARCH 2019 @DESIGNATEDNERD | BAKKENBAECK.NO | JUSTHUM.COM
2. THE TRIUMPHS AND TRIBULATIONS OF KOTLIN/NATIVE IN PRACTICE KOTLIN USERGROUP BELGIUM | BRUSSELS | MARCH 2019 @DESIGNATEDNERD | BAKKENBAECK.NO | JUSTHUM.COM
6. !
7. !
16. THE VIRTUAL MACHINE
22. SHAMELESS PLUG! HTTPS://STORE.RAYWENDERLICH.COM PRODUCTS/KOTLIN-APPRENTICE
28. !
29. PACKAGE THIEF VS. GLITTER BOMB TRAP HTTPS://WWW.YOUTUBE.COM/WATCH?V=XOXHDK-HWUO
46. PACKAGE THIEF VS. GLITTER BOMB TRAP HTTPS://WWW.YOUTUBE.COM/WATCH?V=XOXHDK-HWUO
52. ! "
55. WITH WHAT SYSTEMS SHALL I BUILD IT?
57. Raspberry pi
58. Raspberry pi Server
59. Raspberry pi Server iOS app
60. Raspberry pi Server iOS app Android App
61. Works with Kotlin? Raspberry pi Server iOS app Android App
62. Works With Kotlin? Raspberry pi ✅ Server ✅ iOS app ✅ Android App ✅
63. HTTP://BAKKENBAECK.NO
64. HTTPS://GITHUB.COM/BAKKENBAECK/ PORCH PIRATE PROTECTOR
66. NATIVE VS. MULTI-PLATFORM
67. apply plugin: 'kotlin-multiplatform'
68. apply plugin: 'kotlin-native-platform' apply plugin: 'kotlin-multiplatform'
69. // For Native ONLY projects apply plugin: 'kotlin-native-platform' apply plugin: 'kotlin-multiplatform'
70. // For Native ONLY projects apply plugin: 'kotlin-native-platform' // For projects targeting multiple platforms, // for example JVM + Native + JS apply plugin: 'kotlin-multiplatform'
71. LEARN TO LOVE (TO HATE)
74. PROTIP: USE GRADLE 4.10.1* enableFeaturePreview('GRADLE_METADATA')
75. PROTIP: USE GRADLE 4.10.1* enableFeaturePreview('GRADLE_METADATA') *as of March 21, 2018
78. GET READY TO CARE ABOUT FOLDER STRUCTURE
82. FUNCTIONS WITH PER-PLATFORM IMPLEMENTATIONS expect fun
83. commonMain
84. commonMain
85. iosMain
86. androidMain
87. commonMain
88. CALLING CODE FROM BOTH APPS!
89. ANDROID: EASY MODE build.gradle SomeFragment.kt
90. IOS: MODE
96. ! OBJECTIVE-C
99. IOS/OBJC GOTCHAS
100. SWIFT Array != KOTLIN Array
101. SWIFT Array<T> == KOTLIN List<T>
102. SWIFT enum != KOTLIN enum class IN OBJC
103. KOTLIN enum class DayOfWeek { Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday; }
104. KOTLIN fun printForDay(day: DayOfWeek) { when (day) { DayOfWeek.Monday -> println("You can fall apart") DayOfWeek.Tuesday, DayOfWeek.Wednesday -> println("Break my heart") DayOfWeek.Thursday -> println("Doesn't even start") DayOfWeek.Friday -> println("I'm in love") DayOfWeek.Saturday -> println("Wait") DayOfWeek.Sunday -> print("Always comes too late") } }
106. SWIFT func printForDay(_ day: DayOfWeek) { switch day { case .monday: print("You can fall apart") case .tuesday, .wednesday: print("Break my heart") case .thursday: print("Doesn't even start") case .friday: print("I'm in love") case .saturday: print("Wait") case .sunday: print("Always comes too late") default: fatalError("Not a day") }
107. SWIFT func printForDay(_ day: DayOfWeek) { switch day { case .monday: print("You can fall apart") case .tuesday, .wednesday: print("Break my heart") case .thursday: print("Doesn't even start") case .friday: print("I'm in love") case .saturday: print("Wait") case .sunday: print("Always comes too late") default: fatalError("Not a day") }
108. SWIFT func printForDay(_ day: DayOfWeek) { switch day { case .monday: print("You can fall apart") case .tuesday, .wednesday: print("Break my heart") case .thursday: print("Doesn't even start") case .friday: print("I'm in love") case .saturday: print("Wait") case .sunday: print("Always comes too late") default: // <- ! ! ! fatalError("Not a day") }
109. DECIDING WHAT TO CENTRALIZE
110. WHAT DO I REALLY HATE BUILDING TWICE?
111. TALKING TO THE SERVER
112. JSON FROM NETWORK IN MODELS ⬅ JSON OUT TO NETWORK
118. IosClientEngine.kt https://github.com/ktorio/ktor/blob/master/ ktor-client/ktor-client-ios/darwin/src/io/ ktor/client/engine/ios/IosClientEngine.kt
119. androidMain import kotlinx.coroutines.CoroutineDispatcher import kotlinx.coroutines.Dispatchers internal actual val ApplicationDispatcher: CoroutineDispatcher = Dispatchers.Main
120. iosMain import kotlinx.coroutines.CoroutineDispatcher import kotlinx.coroutines.Dispatchers import platform.darwin.dispatch_async import platform.darwin.dispatch_get_main_queue import kotlin.coroutines.Runnable internal actual val ApplicationDispatcher: CoroutineDispatcher = NsQueueDispatcher() internal class NsQueueDispatcher: CoroutineDispatcher() { override fun dispatch(context: CoroutineContext, block: Runnable) { val queue = dispatch_get_main_queue() dispatch_async(queue) { block.run() } } }
121. iosMain import kotlinx.coroutines.CoroutineDispatcher import kotlinx.coroutines.Dispatchers import platform.darwin.dispatch_async import platform.darwin.dispatch_get_main_queue import kotlin.coroutines.Runnable internal actual val ApplicationDispatcher: CoroutineDispatcher = NsQueueDispatcher() internal class NSQueueDispatcher: CoroutineDispatcher() { override fun dispatch(context: CoroutineContext, block: Runnable) { val queue = dispatch_get_main_queue() dispatch_async(queue) { block.run() } } }
123. ! FREEZING
125. TRY TO AVOID MUTATING VARIABLES
126. AVOID object FROM IOS
127. USE INTERFACES TO MUTATE THINGS IN IOS INSTEAD OF K/N
128. commonMain interface SecureStorage { fun storeTokenString(token: String) fun clearTokenString() fun fetchTokenString(): String? }
129. IOS APP @objc class Keychain: NSObject, SecureStorage { static let shared = Keychain() private override init() { super.init() } //TODO: Actually use keychain private var token: String? func storeTokenString(token: String) { self.token = token } func clearTokenString() { self.token = nil } func fetchTokenString() -> String? { return self.token } }
130. IOS APP @objc class Keychain: NSObject, SecureStorage { static let shared = Keychain() private override init() { super.init() } //TODO: Actually use keychain private var token: String? func storeTokenString(token: String) { self.token = token } func clearTokenString() { self.token = nil } func fetchTokenString() -> String? { return self.token } }
131. IOS APP @objc class Keychain: NSObject, SecureStorage { static let shared = Keychain() private override init() { super.init() } //TODO: Actually use keychain private var token: String? func storeTokenString(token: String) { self.token = token } func clearTokenString() { self.token = nil } func fetchTokenString() -> String? { return self.token } }
132. IOS APP @objc class Keychain: NSObject, SecureStorage { static let shared = Keychain() private override init() { super.init() } //TODO: Actually use keychain private var token: String? func storeTokenString(token: String) { self.token = token } func clearTokenString() { self.token = nil } func fetchTokenString() -> String? { return self.token } }
133. commonMain object TokenManager { fun currentToken(storage: SecureStorage): UserToken? { storage.fetchTokenString()?.let { return UserToken(it) } ?: return null } fun storeToken(token: UserToken, storage: SecureStorage) { storage.storeTokenString(token.token) } fun clearToken(storage: SecureStorage) { storage.clearTokenString() } }
134. commonMain object TokenManager { fun currentToken(storage: SecureStorage): UserToken? { storage.fetchTokenString()?.let { return UserToken(it) } ?: return null } fun storeToken(token: UserToken, storage: SecureStorage) { storage.storeTokenString(token.token) } fun clearToken(storage: SecureStorage) { storage.clearTokenString() } }
135. commonMain object TokenManager { fun currentToken(storage: SecureStorage): UserToken? { storage.fetchTokenString()?.let { return UserToken(it) } ?: return null } fun storeToken(token: UserToken, storage: SecureStorage) { storage.storeTokenString(token.token) } fun clearToken(storage: SecureStorage) { storage.clearTokenString() } }
136. IOS APP @objc class Keychain: NSObject, SecureStorage { static let shared = Keychain() private override init() { super.init() } //TODO: Actually use keychain private var token: String? func storeTokenString(token: String) { self.token = token } func clearTokenString() { self.token = nil } func fetchTokenString() -> String? { return self.token } }
138. KotlinX Serialization
139. commonMain data class UserCredentials( val username: String, val password: String )
140. commonMain apply plugin: 'kotlinx-serialization' @Serializable data class UserCredentials( val username: String, val password: String )
141. commonMain val creds = UserCredentials("lol@ha.no", "guessme") val string = Json.stringify(UserCredentials.serializer(), creds) // String is '{"username":"lol@ha.no","password":"guessme"}' val updatedCreds = Json.parse(UserCredentials.serializer(), string) // updatedCreds.username is "lol@ha.no" // updatedCreds.password is "guessme"
142. commonMain val creds = UserCredentials("lol@ha.no", "guessme") val string = Json.stringify(UserCredentials.serializer(), creds) // String is '{"username":"lol@ha.no","password":"guessme"}' val updatedCreds = Json.parse(UserCredentials.serializer(), string) // updatedCreds.username is "lol@ha.no" // updatedCreds.password is "guessme"
143. commonMain val creds = UserCredentials("lol@ha.no", "guessme") val string = Json.stringify(UserCredentials.serializer(), creds) // String is '{"username":"lol@ha.no","password":"guessme"}' val updatedCreds = Json.parse(UserCredentials.serializer(), string) // updatedCreds.username is "lol@ha.no" // updatedCreds.password is "guessme"
144. commonMain val creds = UserCredentials("lol@ha.no", "guessme") val string = Json.stringify(UserCredentials.serializer(), creds) // String is '{"username":"lol@ha.no","password":"guessme"}' val updatedCreds = Json.parse(UserCredentials.serializer(), string) // updatedCreds.username is "lol@ha.no" // updatedCreds.password is "guessme"
145. commonMain val creds = UserCredentials("lol@ha.no", "guessme") val string = Json.stringify(UserCredentials.serializer(), creds) // String is '{"username":"lol@ha.no","password":"guessme"}' val updatedCreds = Json.parse(UserCredentials.serializer(), string) // updatedCreds.username is "lol@ha.no" // updatedCreds.password is "guessme"
146. FROM CLIENT TO SERVER AND BACK!
147. LOGIC
148. MVC!
149. MVVM!
150. MVA!*
151. MVA!* * - ANYTHING OTHER THAN A MODEL OR A VIEW FOR THE LOVE OF GOD
152. MVP!
153. HTTPS://GITHUB.COM/JETBRAINS/ KOTLINCONF-APP
154. MODEL: VIEW: PRESENTER:
155. MODEL: data class VIEW: PRESENTER:
156. MODEL: data class VIEW: interface PRESENTER:
157. MODEL: data class VIEW: interface PRESENTER: class
158. VIEW: interface
159. IOS VIEW: ANDROID VIEW: TESTING VIEW:
160. IOS VIEW: UIViewController ANDROID VIEW: TESTING VIEW:
161. IOS VIEW: UIViewController ANDROID VIEW: Fragment* TESTING VIEW:
162. IOS VIEW: UIViewController ANDROID VIEW: Fragment* TESTING VIEW: *May not apply if your name is jake wharton
163. IOS VIEW: UIViewController ANDROID VIEW: Fragment* TESTING VIEW: ¯\_(ϑ)_/¯ *May not apply if your name is jake wharton
164. commonMain interface LoginView: IndefiniteLoadingIndicating { /// The text the user has input as their email address. var email: String? /// The text the user has input as their password. var password: String? fun emailErrorUpdated(toString: String?) fun passwordErrorUpdated(toString: String?) fun apiErrorUpdated(toString: String?) fun setSubmitButtonEnabled(enabled: Boolean) /// Called when login completes successfully. fun loginSucceeded() }
165. commonMain class LoginPresenter( val view: LoginView, storage: SecureStorage ): BaseCoroutinePresenter(storage) { // rest of presenter class }
166. commonMain
167. commonMain
168. commonMain
169. ANDROID APP
170. ANDROID APP
171. IOS APP class LoginViewController: UIViewController { @IBOutlet private var emailTextInput: TextInputContainer! @IBOutlet private var passwordTextInput: TextInputContainer! @IBOutlet private var loginButton: UIButton! @IBOutlet private var apiErrorLabel: UILabel! @IBOutlet private var activityIndicator: UIActivityIndicatorView! private lazy var presenter = LoginPresenter(view: self, storage: Keychain.shared) @IBAction private func login() { self.presenter.login() } }
172. extension LoginViewController: LoginView { func setSubmitButtonEnabled(enabled: Bool) { self.loginButton.isEnabled = enabled } func emailErrorUpdated(toString: String?) { self.emailTextInput.errorText = toString } func passwordErrorUpdated(toString: String?) { self.passwordTextInput.errorText = toString } func apiErrorUpdated(toString: String?) { self.apiErrorLabel.text = toString self.apiErrorLabel.isHidden = (toString == nil) } func loginSucceeded() { self.perform(segue: LoginSegue.loginSucceeded) } var email: String? { get { return self.emailTextInput.text } set(email) { self.emailTextInput.text = email } } var password: String? { get { return self.passwordTextInput.text } set(password) { self.passwordTextInput.text = password } } }
173. TESTING YOUR COMMON CODE
174. commonTest WORKS IF COROUTINES AREN'T INVOLVED!
175. class TestLoginView: LoginView { override var email: String? = null override var password: String? = null var submitEnabled = true var submitWasDisabled = false override fun setSubmitButtonEnabled(enabled: Boolean) { submitEnabled = enabled if (!submitEnabled) { submitWasDisabled = true } } var emailError: String? = null override fun emailErrorUpdated(toString: String?) { emailError = toString } var passwordError: String? = null override fun passwordErrorUpdated(toString: String?) { passwordError = toString } var apiError: String? = null override fun apiErrorUpdated(toString: String?) { apiError = toString } var loginHasSucceeded = false override fun loginSucceeded() { loginHasSucceeded = true } }
176. @Test fun validationSetsProperErrorsThenClearsThemAfterChangesMade() { val view = TestLoginView() val presenter = LoginPresenter(view, MockStorage()) presenter.validateAllInput() val expectedEmailError = ValidationResult.Invalid.WasNull("email") val expectedPasswordError = ValidationResult.Invalid.WasNull("password") assertFalse(presenter.isCurrentInputValid()) assertEquals(expectedEmailError.reason, view.emailError) assertEquals(expectedPasswordError.reason, view.passwordError) view.password = "aaaaaa" presenter.validatePassword() assertFalse(presenter.isCurrentInputValid()) assertEquals(expectedEmailError.reason, view.emailError) assertNull(view.passwordError) view.email = "not@real.biz" presenter.validateEmail() assertTrue(presenter.isCurrentInputValid()) assertNull(view.emailError) assertNull(view.passwordError) }
177. @Test fun attemptingToLoginWithoutChangesTriggersErrorsAndFails() = runBlocking { val view = TestLoginView() val presenter = LoginPresenter(view, MockStorage()) val expectedEmailError = ValidationResult.Invalid.WasNull("email") val expectedPasswordError = ValidationResult.Invalid.WasNull("password") val result = presenter.loginAsync() assertFalse(result) assertFalse(presenter.isCurrentInputValid()) // Actual attempt to login should never have been made since // the input was invalid assertFalse(view.submitWasDisabled) assertTrue(view.submitEnabled) assertNull(view.apiError) assertFalse(view.loginHasSucceeded) assertEquals(expectedEmailError.reason, view.emailError) assertEquals(expectedPasswordError.reason, view.passwordError) }
178. @Test fun attemptingToLoginWithoutChangesTriggersErrorsAndFails() = runBlocking { val view = TestLoginView() val presenter = LoginPresenter(view, MockStorage()) val expectedEmailError = ValidationResult.Invalid.WasNull("email") val expectedPasswordError = ValidationResult.Invalid.WasNull("password") val result = presenter.loginAsync() assertFalse(result) assertFalse(presenter.isCurrentInputValid()) // Actual attempt to login should never have been made since // the input was invalid assertFalse(view.submitWasDisabled) assertTrue(view.submitEnabled) assertNull(view.apiError) assertFalse(view.loginHasSucceeded) assertEquals(expectedEmailError.reason, view.emailError) assertEquals(expectedPasswordError.reason, view.passwordError) }
179. runBlocking DOESN'T EXIST FOR ALL PLATFORMS
180. JAVASCRIIIIIIIIPT!
181. commonTest expect fun <T> platformRunBlocking( block: suspend CoroutineScope.() -> T ) : T
182. commonTest expect fun <T> platformRunBlocking( block: suspend CoroutineScope.() -> T ) : T androidTest actual fun <T> platformRunBlocking( block: suspend CoroutineScope.() -> T ): T { return runBlocking { block() } }
183. commonTest expect fun <T> platformRunBlocking( block: suspend CoroutineScope.() -> T ) : T androidTest + iosTest actual fun <T> platformRunBlocking( block: suspend CoroutineScope.() -> T ): T { return runBlocking { block() } }
184. @Test fun attemptingToLoginWithoutChangesTriggersErrorsAndFails() = platformBlocking { val view = TestLoginView() val presenter = LoginPresenter(view, MockStorage()) val expectedEmailError = ValidationResult.Invalid.WasNull("email") val expectedPasswordError = ValidationResult.Invalid.WasNull("password") val result = presenter.loginAsync() assertFalse(result) assertFalse(presenter.isCurrentInputValid()) // Actual attempt to login should never have been made since // the input was invalid assertFalse(view.submitWasDisabled) assertTrue(view.submitEnabled) assertNull(view.apiError) assertFalse(view.loginHasSucceeded) assertEquals(expectedEmailError.reason, view.emailError) assertEquals(expectedPasswordError.reason, view.passwordError) }
186. androidTest WILL ALSO RUN YOUR commonTest TESTS!
189. THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT
190. THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT (WHICH HAVE LITTLE TO NOTHING TO DO WITH KOTLIN)
191. THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT > Docker
192. THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT > Docker > MySQL
193. THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT > Docker > MySQL > ORMs for MySQL
194. THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT > Docker > MySQL > ORMs for MySQL > One-way hashing for secure password storage
195. THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT > Docker > MySQL > ORMs for MySQL > One-way hashing for secure password storage > Your computer's exact melting point
200. DO WE HAVE TIME FOR A TERRIBLE IDEA?
201. AND NOW, A TERRIBLE IDEA: A LIVE DEMO!
202. !"# NEXT STEPS
203. !"# NEXT STEPS > Build the prototype box
204. !"# NEXT STEPS > Build the prototype box > Get the Raspberry pi software working
205. !"# NEXT STEPS > Build the prototype box > Get the Raspberry pi software working > Get the raspberry pi actually unlocking the box
206. !"# NEXT STEPS > Build the prototype box > Get the Raspberry pi software working > Get the raspberry pi actually unlocking the box > Work on sharing design elements
207. !"# NEXT STEPS > Build the prototype box > Get the Raspberry pi software working > Get the raspberry pi actually unlocking the box > Work on sharing design elements > Work on sharing localized strings
208. !"# NEXT STEPS > Build the prototype box > Get the Raspberry pi software working > Get the raspberry pi actually unlocking the box > Work on sharing design elements > Work on sharing localized strings > Maybe find someone who knows what they're doing to build it for real?
209. OBLIGATORY SUMMARY SLIDE!
210. OBLIGATORY SUMMARY SLIDE! > Kotlin/Native has made great strides in the last year
211. OBLIGATORY SUMMARY SLIDE! > Kotlin/Native has made great strides in the last year > Share logic across iOS, android, and server without killing performance or sacrificing type/null safety
212. OBLIGATORY SUMMARY SLIDE! > Kotlin/Native has made great strides in the last year > Share logic across iOS, android, and server without killing performance or sacrificing type/null safety > it's still beta, You will run into a lot of brick walls
213. OBLIGATORY SUMMARY SLIDE! > Kotlin/Native has made great strides in the last year > Share logic across iOS, android, and server without killing performance or sacrificing type/null safety > it's still beta, You will run into a lot of brick walls > Ktor and kotlinX serialization are a huge help, if you can get around what a mess coroutines can be on iOS
214. OBLIGATORY SUMMARY SLIDE! > Kotlin/Native has made great strides in the last year > Share logic across iOS, android, and server without killing performance or sacrificing type/null safety > it's still beta, You will run into a lot of brick walls > Ktor and kotlinX serialization are a huge help, if you can get around what a mess coroutines can be on iOS > This is experimental, but it's stupid amounts of fun
216. LINKS! > Kotlin MPP for iOS + Android tutorial https://kotlinlang.org/docs/tutorials/ native/mpp-ios-android.html > KotlinConf App https://github.com/JetBrains/kotlinconf- app > KotlinLang Slack https://slack.kotlinlang.org
217. LINKS! > My original Kotlin Native sandbox https://github.com/designatednerd/ KotlinNativeTest > Package Thief vs. Glitter Bomb Trap https://youtube.com/watch?v=xoxhDk-hwuo