Kotlin Multiplatform Mobile: From Hello World to Production

Droidcon London version

Transcript

1. Pamela Hill & Tadeas Kriz Kotlin Multiplatform Mobile From Hello World to Production @pamelaahill @TadeasKriz
2. Pamela Hill Developer Advocate at JetBrains @pamelaahill
3. Tadeas Kriz Senior Mobile Developer at Touchlab @TadeasKriz
4. Topics • Introduction • Use Case Scenarios • Application Architecture • Testing • Debugging Crashes • Closing • Q&A Introduction Use Case Scenarios Architecture Testing Debugging Crashes Closing
5. Introduction
6. What is Kotlin Multiplatform Mobile? • SDK by JetBrains, beta earlier in October • Allows development teams to share common code • Doesn't impose restrictions on non-shared code
7. .framework What is Kotlin Multiplatform Mobile? Android App iOS App Kotlin/JVM Kotlin/Native MySharedModule .jar/.aar
8. How can you share code? iOS App Multiplatform Mobile Module (Shared) Android App Presentation (Presenters, View Models, Controllers) UI (Views) Presentation (Presenters, View Models, Controllers) UI (Views) Data / Core (Repositories, HTTP Clients, Cache) Business / Domain (Entities, Use Cases, Interactors)
9. How can you share code? iOS App Multiplatform Mobile Module (Shared) Android App Presentation (Presenters, View Models, Controllers) UI (Views) UI (Views) Data / Core (Repositories, HTTP Clients, Cache) Business / Domain (Entities, Use Cases, Interactors)
10. What are the bene f its of Kotlin Multiplatform Mobile? • Flexibility to choose what is shared and what not 
 • Shared code lowers the e ff ort, cost per feature 
 • Shared code ensures consistency amongst platforms
11. Use Case Scenarios
12. Green f ield project #1 Kotlin Multiplatform Mobile Project shared <KMM module> androidApp <module> iosApp <module> commonMain <source set> iosMain <source set> androidMain <source set>
13. Green f ield project #2 Kotlin Multiplatform Mobile Project androidApp <module> iosApp <module> analytics <KMM module> validation <KMM module> formatting <KMM module>
14. Brown f ield project #1 Android Project Regular Android code shared <module> commonMain <source set> iosMain <source set> androidMain <source set> iOS Project Regular iOS code Dependencies management • CocoaPods • Swift Package Manager • Manual framework
15. Brown f ield project #2 Android Project Regular Android code analytics <KMM module> iOS Project Regular iOS code validation <KMM module> formatting <KMM module> shared <KMM module> Dependencies management • CocoaPods • Swift Package Manager • Manual framework
16. Brown f ield project #3 analytics <KMM library> validation <KMM library> formatting <KMM library> iOS Project Regular iOS code Android Project Regular Android code
17. KMMBridge Android App Swift / Obj-C iOS App Framework Releases 1.2.0 1.2.1 … SPM/Cocoapods KMMBridge Android / Kotlin
18. Adding Multiplatform Mobile to Your Projects • Start small • Keep your shared API simple • Think like a library developer • Implementation should not impact API • Minimise accessibility of everything • Coexist peacefully with (both) platforms
19. Application Architecture
20. No Silver Bullets
21. Multi-layer Architecture
22. Multi-layer Architecture Data Domain Presentation
23. Presentation Layer • Sharing is possible to a degree • Prefer MVVM and MVI • Decompose, moko-mvvm • Needs experienced team to share
24. Domain Layer • Perfectly shareable • Services, Models, Gateways
25. Data Layer • Usually shareable • Repositories, DTOs and entities • SQLDelight, Realm, Ktor Client, Apollo, kotlinx-datetime
26. Multiplatform UI
27. Dependency Injection
28. Testing
29. Project Structure Kotlin Multiplatform Mobile Project shared <KMM module> androidApp <module> iosApp <module> androidMain <source set> androidTest <source set> commonMain <source set> commonTest <source set> iosMain <source set> iosTest <source set>
30. Testing Shared Code shared/build.gradle.kts val commonTest by getting { dependencies { implementation(kotlin("test-common")) implementation(kotlin("test-annotations-common")) } } val androidTest by getting { dependencies { implementation(kotlin("test-junit")) implementation("junit:junit:4.13.2") } }
31. Testing Shared Code commonMain/../NewYear.kt import kotlinx.datetime.* fun daysUntilNewYear( today: LocalDate = Clock.System.todayIn(TimeZone.currentSystemDefault()) ): Int { val closestNewYear = LocalDate(today.year + 1, 1, 1) return today.daysUntil(closestNewYear) }
32. Testing Shared Code commonTest/…/NewYearTest.kt import kotlinx.datetime.LocalDate import kotlin.test.Test import kotlin.test.assertEquals class NewYearTest { @Test fun `From Jan 1 2022 to Jan 1 2023`() { val startDate = LocalDate( year = 2022, monthNumber = 1, dayOfMonth = 1 ) assertEquals( expected = 365, actual = daysUntilNewYear(startDate), "There are x days until New Year 2023" ) } }
33. Testing expect/actual //commonMain expect class Platform() { val osName: String } //androidMain actual class Platform actual constructor() { actual val osName = "Android" } //iosMain actual class Platform actual constructor() { actual val osName = UIDevice.currentDevice.systemName() }
34. Testing expect/actual commonTest/../PlatformTest.kt expect class PlatformTest { @Test fun testOSName() }
35. Testing expect/actual androidTest/../PlatformTest.kt actual class PlatformTest { private val platform = Platform() @Test actual fun testOSName() { assertEquals( expected = "Android", actual = platform.osName, message = "The OS name should be Android." ) } }
36. Testing expect/actual iosTest/../PlatformTest.kt actual class PlatformTest { private val platform = Platform() @Test actual fun testOSName() { assertTrue( actual = platform.osName.equals("iOS", ignoreCase = true) message = "The OS name should be iOS." ) } }
37. MocKMP Multiplatform framework for creating mocks and fakes class MyTests : TestsWithMocks() { override fun setUpMocks() = injectMocks(mocker) @Mock lateinit var view: View @Fake lateinit var model: Model val controller by withMocks { Controller( view = view, firstModel = model ) } ... }
38. iOS UI Testing File > New > Target
39. iOS UI Testing iosApp/…/iosAppUITests.swift import XCTest class iosAppUITests: XCTestCase { private let app = XCUIApplication() override func setUp() { super.setUp() continueAfterFailure = false app.launch() } func testButtonExistence() { XCTAssert(app.buttons["clickMeButton"].exists) } }
40. Debugging Crashes
41. Errors and Exceptions
42. Errors and Exceptions Swift and ObjC func iThrow() throws { throw NSError() } func iCrash() { fatalError() } -(BOOL)iThrow:(NSError**)error { *error = [[NSError alloc] init]; return NO; } -(void)iCrash { [NSException raise:@"Oops" format:@""]; } Recoverable Unrecoverable
43. Errors and Exceptions Kotlin vs Swift func iThrow() throws { throw NSError() } func iCrash() { fatalError() } @Throws(IllegalStateException::class) fun iThrow() { throw IllegalStateException() } fun iCrash() { throw IllegalStateException() }
44. Stacktrace, where art thou
45. CrashKiOS NSExceptionKt Kermit
46. New Memory Model 🥳
47. Reproduce on iOS
48. Write a test
49. Reproduce on Android
50. Debugging in Xcode
51. xcode-kotlin https://github.com/touchlab/xcode-kotlin
52. Add Kotlin code
53. Breakpoints
56. Hello println, my old friend.
57. Closing
58. Key Points • Kotlin Multiplatform Mobile is powerful, but challenging • No silver bullets • Use it now, it's ready!
59. Slides bit.ly/kmm-hw2p-slides
60. Resources bit.ly/kmm-hw2p-resources
61. Thank you, any questions? We have stickers