All aboard the Metro

Presentation for the Paris Android User Group January 13th at chez amo.

We'll explore the newest Dependency Injection framework called Metro and how it compares to Hilt

Transcript

1. All Aboard the Metro A Journey Migrating Away from Hilt Jonas Pedersen
2. What is Metro?
3. What is Metro? - Dependency Injection library for Kotlin - Kotlin compiler plugin - Authored by Zac Sweers (Slack, Uber) https://zacsweers.github.io/metro/latest/
4. What is Metro? https://www.youtube.com/watch?v=jVfmtVKa604
5. This presentation - Compare Hilt and Metro - Why switch? - How to switch? - Result of switching
6. What is Dependency Injection?
7. What is Dependency Injection? class WeatherApp { fun run(location: String) { val service = WeatherService() val formatter = WeatherFormatter() val forecast = service.getForecast(location) println(formatter.format(forecast)) } }
8. What is Dependency Injection? class WeatherApp { fun run(location: String) { val service = WeatherService() val formatter = WeatherFormatter() val forecast = service.getForecast(location) println(formatter.format(forecast)) } }
9. What is Dependency Injection? class WeatherApp constructor( private val service: WeatherService, private val formatter: WeatherFormatter ) { lateinit var printer: WeatherPrinter /// ..... }
10. What is Dependency Injection? class WeatherApp constructor( private val service: WeatherService, private val formatter: WeatherFormatter ) { lateinit var printer: WeatherPrinter /// ..... } fun main() { val service = WeatherService() val formatter = WeatherFormatter() val app = WeatherApp(service, formatter) app.printer = WeatherPrinter() }
11. What is Dependency Injection? class WeatherApp constructor( private val service: WeatherService, private val formatter: WeatherFormatter ) { lateinit var printer: WeatherPrinter /// ..... } fun main() { val service = WeatherService() val formatter = WeatherFormatter() val app = WeatherApp(service, formatter) app.printer = WeatherPrinter() }
12. What is Dependency Injection? class WeatherApp constructor( private val service: WeatherService, private val formatter: WeatherFormatter ) { lateinit var printer: WeatherPrinter /// ..... } fun main() { val service = WeatherService() val formatter = WeatherFormatter() val app = WeatherApp(service, formatter) app.printer = WeatherPrinter() }
13. What is Dependency Injection? class WeatherApp constructor( private val service: WeatherService, private val formatter: WeatherFormatter ) { lateinit var printer: WeatherPrinter /// ..... } fun main() { val service = WeatherService() val formatter = WeatherFormatter() val app = WeatherApp(service, formatter) app.printer = WeatherPrinter() }
14. What is Dependency Injection? class WeatherApp @Inject constructor( private val service: WeatherService, private val formatter: WeatherFormatter ) { @Inject lateinit var printer: WeatherPrinter /// ..... }
15. Hilt
16. Hilt - Dependency Injection library for Android - Annotation processor (KAPT, KSP) - Built on Dagger - Maintained and Recommended by Google
17. What is the problem with Hilt?
18. What is the problem with Hilt?
19. What is the problem with Hilt?
20. What is the problem with Hilt?
21. What is the problem with Hilt? 100% Kotlin
22. What is the problem with Hilt?
23. What is the problem with Hilt?
24. What is the problem with Hilt?
25. What is the problem with Hilt?
26. What is the problem with Hilt? Hilt Metro
27. What is the problem with Hilt?
28. What is the problem with Hilt? https://www.youtube.com/watch?v=SmGisVJ549w
29. Hilt -> Metro
30. Hilt -> Metro interface WeatherService class WeatherServiceImpl @Inject constructor(): WeatherService { // ... } @HiltAndroidApp class WeatherApplication : Application() @HiltEntryPoint(ComponentActivity::class) class WeatherActivity : ComponentActivity() {} @HiltViewModel class WeatherViewModel @Inject constructor(val service: WeatherService) : ViewModel()
31. Hilt -> Metro interface WeatherService class WeatherServiceImpl @Inject constructor(): WeatherService { // ... } @HiltAndroidApp class WeatherApplication : Application() @HiltEntryPoint(ComponentActivity::class) class WeatherActivity : ComponentActivity() {} @HiltViewModel class WeatherViewModel @Inject constructor(val service: WeatherService) : ViewModel()
32. Hilt -> Metro https://zacsweers.github.io/metro/latest/adoption/ // build.gradle.kts metro { interop { includeDagger() } }
33. Hilt -> Metro @Component class SingletonComponent @DependencyGraph interface AppGraph Defined by HILT Created by us
34. Hilt -> Metro @DependencyGraph(AppScope::class) interface WeatherAppGraph { @Binds @ApplicationContext val Application.binds: Context fun inject(app: WeatherApplication) @DependencyGraph.Factory interface Factory { fun create(@Provides app: Application): WeatherAppGraph } }
35. Hilt -> Metro @DependencyGraph(AppScope::class) interface WeatherAppGraph { @Binds @ApplicationContext val Application.binds: Context fun inject(app: WeatherApplication) @DependencyGraph.Factory interface Factory { fun create(@Provides app: Application): WeatherAppGraph } }
36. Hilt -> Metro @DependencyGraph(AppScope::class) interface WeatherAppGraph { @Binds @ApplicationContext val Application.binds: Context fun inject(app: WeatherApplication) @DependencyGraph.Factory interface Factory { fun create(@Provides app: Application): WeatherAppGraph } }
37. Hilt -> Metro @DependencyGraph(AppScope::class) interface WeatherAppGraph { @Binds @ApplicationContext val Application.binds: Context fun inject(app: WeatherApplication) @DependencyGraph.Factory interface Factory { fun create(@Provides app: Application): WeatherAppGraph } }
38. Hilt -> Metro @DependencyGraph(AppScope::class) interface WeatherAppGraph { @Binds @ApplicationContext val Application.binds: Context fun inject(app: WeatherApplication) @DependencyGraph.Factory interface Factory { fun create(@Provides app: Application): WeatherAppGraph } }
39. Hilt -> Metro class WeatherApplication : Application() { val graph by lazy { createGraphFactory<WeatherAppGraph.Factory>().create(this) } @Inject lateinit var logger: Logger override fun onCreate() { super.onCreate() graph.inject(this) } }
40. Hilt -> Metro class WeatherApplication : Application() { val graph by lazy { createGraphFactory<WeatherAppGraph.Factory>().create(this) } @Inject lateinit var logger: Logger override fun onCreate() { super.onCreate() graph.inject(this) } }
41. Hilt -> Metro class WeatherApplication : Application() { val graph by lazy { createGraphFactory<WeatherAppGraph.Factory>().create(this) } @Inject lateinit var logger: Logger override fun onCreate() { super.onCreate() graph.inject(this) } }
42. Hilt -> Metro @Subcomponent class ActivityRetainedComponent @GraphExtension interface ActivityRetainedGraph Defined by HILT Created by us
43. Hilt -> Metro @GraphExtension(ActivityRetainedScoped::class) interface WeatherActivityRetainedGraph { @ContributesTo(AppScope::class) @GraphExtension.Factory interface Factory { fun createWeatherActivityRetainedGraph(): WeatherActivityRetainedGraph } }
44. Hilt -> Metro @GraphExtension(ActivityRetainedScoped::class) interface WeatherActivityRetainedGraph { @ContributesTo(AppScope::class) @GraphExtension.Factory interface Factory { fun createWeatherActivityRetainedGraph(): WeatherActivityRetainedGraph } }
45. Hilt -> Metro @GraphExtension(ActivityRetainedScoped::class) interface WeatherActivityRetainedGraph { @ContributesTo(AppScope::class) @GraphExtension.Factory interface Factory { fun createWeatherActivityRetainedGraph(): WeatherActivityRetainedGraph } }
46. Hilt -> Metro @GraphExtension(ActivityRetainedScoped::class) interface WeatherActivityRetainedGraph { @ContributesTo(AppScope::class) @GraphExtension.Factory interface Factory { fun createWeatherActivityRetainedGraph(): WeatherActivityRetainedGraph } }
47. Hilt -> Metro class WeatherActivity : ComponentActivity() { val activityRetained by viewModels<ActivityRetainedViewModel> { object : ViewModelProvider.Factory { override fun <T : ViewModel> create(modelClass: Class<T>): T { val app = applicationContext as WeatherApplication val graph = (app.graph as WeatherActivityRetainedGraph.Factory) .createWeatherActivityRetainedGraph() @Suppress("UNCHECKED_CAST") return ActivityRetainedViewModel(graph) as T } } } } class ActivityRetainedViewModel(val graph: WeatherActivityRetainedGraph) : ViewModel()
48. Hilt -> Metro class WeatherActivity : ComponentActivity() { val activityRetained by viewModels<ActivityRetainedViewModel> { object : ViewModelProvider.Factory { override fun <T : ViewModel> create(modelClass: Class<T>): T { val app = applicationContext as WeatherApplication val graph = (app.graph as WeatherActivityRetainedGraph.Factory) .createWeatherActivityRetainedGraph() @Suppress("UNCHECKED_CAST") return ActivityRetainedViewModel(graph) as T } } } } class ActivityRetainedViewModel(val graph: WeatherActivityRetainedGraph) : ViewModel()
49. Hilt -> Metro class WeatherActivity : ComponentActivity() { val activityRetained by viewModels<ActivityRetainedViewModel> { object : ViewModelProvider.Factory { override fun <T : ViewModel> create(modelClass: Class<T>): T { val app = applicationContext as WeatherApplication val graph = (app.graph as WeatherActivityRetainedGraph.Factory) .createWeatherActivityRetainedGraph() @Suppress("UNCHECKED_CAST") return ActivityRetainedViewModel(graph) as T } } } } class ActivityRetainedViewModel(val graph: WeatherActivityRetainedGraph) : ViewModel()
50. Hilt -> Metro class WeatherActivity : ComponentActivity() { val activityRetained by viewModels<ActivityRetainedViewModel> { object : ViewModelProvider.Factory { override fun <T : ViewModel> create(modelClass: Class<T>): T { val app = applicationContext as WeatherApplication val graph = (app.graph as WeatherActivityRetainedGraph.Factory) .createWeatherActivityRetainedGraph() @Suppress("UNCHECKED_CAST") return ActivityRetainedViewModel(graph) as T } } } } class ActivityRetainedViewModel(val graph: WeatherActivityRetainedGraph) : ViewModel()
51. Hilt -> Metro class WeatherActivity : ComponentActivity() { val activityRetained by viewModels<ActivityRetainedViewModel> { object : ViewModelProvider.Factory { override fun <T : ViewModel> create(modelClass: Class<T>): T { val app = applicationContext as WeatherApplication val graph = (app.graph as WeatherActivityRetainedGraph.Factory) .createWeatherActivityRetainedGraph() @Suppress("UNCHECKED_CAST") return ActivityRetainedViewModel(graph) as T } } } } class ActivityRetainedViewModel(val graph: WeatherActivityRetainedGraph) : ViewModel()
52. Hilt -> Metro @GraphExtension(ActivityScoped::class) interface ActivityGraph { @ContributesTo(ActivityRetainedScoped::class) @GraphExtension.Factory interface Factory { fun createActivityGraph(): ActivityGraph } } @GraphExtension(ViewModelScoped::class) interface ViewModelGraph { @ContributesTo(ActivityRetainedScoped::class) @GraphExtension.Factory interface Factory { fun createViewModelGraph(): ViewModelGraph } }
53. Hilt -> Metro @GraphExtension(ActivityScoped::class) interface ActivityGraph { @ContributesTo(ActivityRetainedScoped::class) @GraphExtension.Factory interface Factory { fun createActivityGraph(): ActivityGraph } } @GraphExtension(ViewModelScoped::class) interface ViewModelGraph { @ContributesTo(ActivityRetainedScoped::class) @GraphExtension.Factory interface Factory { fun createViewModelGraph(): ViewModelGraph } }
54. Hilt -> Metro @GraphExtension(ActivityScoped::class) interface ActivityGraph { @ContributesTo(ActivityRetainedScoped::class) @GraphExtension.Factory interface Factory { fun createActivityGraph(): ActivityGraph } } @GraphExtension(ViewModelScoped::class) interface ViewModelGraph { @ContributesTo(ActivityRetainedScoped::class) @GraphExtension.Factory interface Factory { fun createViewModelGraph(): ViewModelGraph } }
55. Hilt -> Metro // HILT @Module @InstallIn(SingletonComponent::class) interface WeatherModule { @Binds fun bindWeatherService(impl: WeatherServiceImpl): WeatherService } Bindings
56. Hilt -> Metro // HILT @Module @InstallIn(SingletonComponent::class) interface WeatherModule { @Binds fun bindWeatherService(impl: WeatherServiceImpl): WeatherService } // Metro @BindingContainer // Optionally find/replace @Module @ContributesTo(AppScope::class) interface WeatherModule { @Binds fun bindWeatherService(impl: WeatherServiceImpl): WeatherService } Bindings
57. Hilt -> Metro // HILT @Module @InstallIn(SingletonComponent::class) interface WeatherModule { @Binds fun bindWeatherService(impl: WeatherServiceImpl): WeatherService } // Metro @BindingContainer // Optionally find/replace @Module @ContributesTo(AppScope::class) interface WeatherModule { @Binds fun bindWeatherService(impl: WeatherServiceImpl): WeatherService } Bindings
58. Hilt -> Metro // HILT @Module @InstallIn(SingletonComponent::class) interface WeatherModule { @Binds fun bindWeatherService(impl: WeatherServiceImpl): WeatherService } // Metro @BindingContainer // Optionally find/replace @Module @ContributesTo(AppScope::class) interface WeatherModule { @Binds fun bindWeatherService(impl: WeatherServiceImpl): WeatherService } @ContributesBinding(AppScope::class) class WeatherServiceImpl : WeatherService { Bindings
59. Hilt -> Metro ViewModel https://zacsweers.github.io/metro/latest/metrox-viewmodel/ @Inject @ContributesBinding(AppScope::class) @SingleIn(AppScope::class) class MyViewModelFactory( override val viewModelProviders: Map<KClass<out ViewModel>, Provider<ViewModel>>, override val assistedFactoryProviders: Map<KClass<out ViewModel>, Provider<ViewModelAssistedFactory>>, override val manualAssistedFactoryProviders: Map<KClass<out ManualViewModelAssistedFactory>, Provider<ManualViewMo ) : MetroViewModelFactory()
60. Hilt -> Metro ViewModel @Composable fun WeatherScreen(viewModel: WeatherViewModel = metroViewModel()) { } @ContributesIntoMap(ViewModelScoped::class) @ViewModelKey(WeatherViewModel::class) class WeatherViewModel(val service: WeatherService) : ViewModel()
61. Hilt -> Metro EntryPoints / Inject in compose val LocalViewGraph = compositionLocalOf<ViewGraph> { error("ViewGraph not set") }
62. Hilt -> Metro EntryPoints / Inject in compose val LocalViewGraph = compositionLocalOf<ViewGraph> { error("ViewGraph not set") } @ContributesTo(ViewScoped::class) interface WeatherContribution { val formatter: WeatherFormatter }
63. Hilt -> Metro EntryPoints / Inject in compose val LocalViewGraph = compositionLocalOf<ViewGraph> { error("ViewGraph not set") } @ContributesTo(ViewScoped::class) interface WeatherContribution { val formatter: WeatherFormatter } not a Module / BindingContainer
64. Hilt -> Metro EntryPoints / Inject in compose val LocalViewGraph = compositionLocalOf<ViewGraph> { error("ViewGraph not set") } @ContributesTo(ViewScoped::class) interface WeatherContribution { val formatter: WeatherFormatter } @Composable inline fun <reified T> contribution(): T { return LocalViewGraph.current as T }
65. Hilt -> Metro EntryPoints / Inject in compose val LocalViewGraph = compositionLocalOf<ViewGraph> { error("ViewGraph not set") } @ContributesTo(ViewScoped::class) interface WeatherContribution { val formatter: WeatherFormatter } @Composable inline fun <reified T> contribution(): T { return LocalViewGraph.current as T } @Composable fun WeatherScreen() { val contribution = contribution<WeatherContribution>() val formatter = remember { contribution.formatter } }
66. Hilt -> Metro EntryPoints / Inject in compose val LocalViewGraph = compositionLocalOf<ViewGraph> { error("ViewGraph not set") } @ContributesTo(ViewScoped::class) interface WeatherContribution { val formatter: WeatherFormatter } @Composable inline fun <reified T> contribution(): T { return LocalViewGraph.current as T } @Composable fun WeatherScreen() { val contribution = LocalViewGraph.current.asContribution<WeatherContribution>() val formatter = remember { contribution.formatter } }
67. What are the results? BEFORE apps: 5 components: 333 platform: 130 foundation: 13 TOTAL: 482 AFTER apps: 5 components: 211 platform: 127 foundation: 13 TOTAL: 357 -125 modules -25% modules
68. What are the results? -5000 loc -2,5% loc
69. What are the results? -5000 loc -2,5% loc
70. What are the results? Build times
71. What are the results? :assembleDebug with ABI change Build times
72. What are the results? :assembleDebug with ABI change Build times hilt 24s metro 8,5s
73. What are the results? :assembleDebug with ABI change Build times hilt 24s metro 8,5s 65% faster
74. What are the results? https://zacsweers.github.io/metro/latest/performance/ Build times ABI change
75. What are the results? https://zacsweers.github.io/metro/latest/performance/ Build times Non-ABI change
76. So why not Koin?
77. So why not Koin? - Static analysis is a non-negotiable for us
78. So why not Koin? - Static analysis is a non-negotiable for us - Koin-annotations uses KSP
79. Any downsides? - Still pretty new - Some corner cases not found can lead to confusing error messages - Still not v1.0, API can technically still change - Android Studio support
80. What else? - Multibindings - Optionals - Multiplatform - Top level function injection - Assisted injection
81. Thank You Jonas Pedersen