Investing in Koin

Thanks to its clean design, Koin is quickly gaining popularity as an IoC framework. Highlights include its excellent documentation, accessible api, and the pure Kotlin source.

In this talk, we’ll go over basic usage like factories, singles, and modules. We’ll talk about scoping and lazy-loading modules, and we’ll look at its integration with Android screens and ViewModels. Most importantly, we’ll see how we can use Koin to easily generate mocked dependencies for clean and hermetic tests.

Transcript

1. @rbusarow INVESTING
 IN KOIN Rick Busarow rickbusarow@gmail.com
2. @rbusarow Screen ViewModel UserId Repository Dao Room Database App Context Service Retrofit OkHttpClient Base Url
3. @rbusarow Normal Control Flow
4. @rbusarow class MyRepository { internal val database: MyDatabase = MyDatabase.init(APP_CONTEXT) internal val okHttpClient: OkHttpClient = OkHttpClient() internal val retrofit: Retrofit = Retrofit.Builder() .baseUrl("https://example.dev") .client(okHttpClient) .build() internal val service: MyService = retrofit.create<MyService>() internal val dao: MyDao = TODO() } Normal Control Flow
5. @rbusarow Inversion of Control
6. @rbusarow Service Location Dependency Injection Inversion of Control
7. @rbusarow Service Location Dependency Injection class ViewModel { val repository = Locator.createRepository() } Inversion of Control
8. @rbusarow Service Location Dependency Injection class ViewModel { val repository = Locator.createRepository() } class ViewModel(val repository: Repository) { lateinit var otherDependency : OtherDependency } Inversion of Control
9. Inversion of Control @rbusarow class ViewModel(locator: Locator) { val repository = locator.createRepository() } class ViewModel(val repository: Repository) { lateinit var otherDependency : OtherDependency } Service Location Dependency Injection
10. @rbusarow Field Injection
11. @rbusarow class Screen : Fragment() { lateinit var viewModel: ViewModel } Field Injection
12. class Screen : Fragment() { lateinit var viewModel: ViewModel override fun onAttach(context: Context) { Injector.inject(this) super.onAttach(context) } } object Injector { fun inject(screen: Screen) { screen.viewModel = TODO() } } @rbusarow Field Injection
13. class Screen : Fragment() { lateinit var viewModel: ViewModel override fun onAttach(context: Context) { Injector.inject(this) super.onAttach(context) } } object Injector { fun inject(screen: Screen) { screen.viewModel = TODO() } } @rbusarow Field Injection
14. @rbusarow class Screen : Fragment() { lateinit var viewModel: ViewModel override fun onAttach(context: Context) { Injector.inject(this) super.onAttach(context) } } object Injector { fun inject(screen: Screen) { screen.viewModel = TODO() } } Field Injection
15. @rbusarow class Screen : Fragment() { lateinit var viewModel: ViewModel override fun onAttach(context: Context) { Injector.inject(this) super.onAttach(context) } } object Injector { fun inject(screen: Screen) { screen.viewModel = TODO() } } Field Injection public mutable late init
16. @rbusarow class ViewModel(val repository: Repository) Dependency Injection
17. class Screen { val repository: Repository = TODO() val viewModel = ViewModel(repository) fun onCreate() { viewModel.observe { ... } } } class ViewModel(val repository: Repository) @rbusarow Dependency Injection
18. class Screen(repository: Repository) { val viewModel = ViewModel(repository) fun onCreate() { viewModel.observe { ... } } } class ViewModel(val repository: Repository) @rbusarow Dependency Injection
19. class Screen(val viewModel: ViewModel) { fun onCreate() { viewModel.observe { ... } } } class ViewModel(val repository: Repository) @rbusarow Dependency Injection
20. class Screen(val viewModel: ViewModel) { fun onCreate() { viewModel.observe { ... } } } class ViewModel(val repository: Repository) @rbusarow Dependency Injection
21. class Screen(val viewModel: ViewModel) { fun onCreate() { viewModel.observe { ... } } } class ViewModel(val repository: Repository) @rbusarow Dependency Injection
22. class Screen { // lazy init val viewModel by ViewModelProvider.get<ViewModel>(this) fun onCreate() { viewModel.observe { ... } } } class ViewModel(val repository: Repository) @rbusarow Dependency Injection
23. class Screen { // lazy init val viewModel by Locator.get<ViewModel>(this) fun onCreate() { viewModel.observe { ... } } } class ViewModel(val repository: Repository) @rbusarow Dependency Injection
24. @rbusarow Koin KoinApplication
25. class Koin { val graph: Graph fun <T> inject(): Lazy<T> fun <T> get(): T fun <S, P> bind(s: S): S fun createScope(scopeId: ScopeID, qualifier: Qualifier): Scope } class KoinApplication { val koin = Koin() fun modules(modules: List<Module>): KoinApplication fun logger(logger: Logger): KoinApplication fun unloadModules(modules: List<Module>) fun close() } @rbusarow Koin & KoinApplication
26. class Koin { val graph: Graph fun <T> inject(): Lazy<T> fun <T> get(): T fun <S, P> bind(s: S): S fun createScope(scopeId: ScopeID, qualifier: Qualifier): Scope } class KoinApplication { val koin = Koin() fun modules(modules: List<Module>): KoinApplication fun logger(logger: Logger): KoinApplication fun unloadModules(modules: List<Module>) fun close() } @rbusarow Koin & KoinApplication
27. class Koin { val graph: Graph fun <T> inject(): Lazy<T> fun <T> get(): T fun <S, P> bind(s: S): S fun createScope(scopeId: ScopeID, qualifier: Qualifier): Scope } class KoinApplication { val koin = Koin() fun modules(modules: List<Module>): KoinApplication fun logger(logger: Logger): KoinApplication fun unloadModules(modules: List<Module>) fun close() } @rbusarow Koin & KoinApplication Not an Android Application
28. @rbusarow GlobalContext
29. @rbusarow object GlobalContext { internal var app: KoinApplication? = null fun get(): KoinApplication fun getOrNull(): KoinApplication? fun start(koinApplication: KoinApplication) fun stop() = synchronized(this) { app?.close() app = null } } GlobalContext
30. @rbusarow startKoin( ) koinApplication( )
31. @rbusarow fun startKoin(appDeclaration: KoinAppDeclaration): KoinApplication { val koinApplication = KoinApplication.create() GlobalContext.start(koinApplication) appDeclaration(koinApplication) koinApplication.createEagerInstances() return koinApplication } fun koinApplication(appDeclaration: KoinAppDeclaration): KoinApplication { val koinApplication = KoinApplication.create() appDeclaration(koinApplication) return koinApplication } startKoin & koinApplication
32. @rbusarow fun startKoin(appDeclaration: KoinAppDeclaration): KoinApplication { val koinApplication = KoinApplication.create() GlobalContext.start(koinApplication) appDeclaration(koinApplication) koinApplication.createEagerInstances() return koinApplication } fun koinApplication(appDeclaration: KoinAppDeclaration): KoinApplication { val koinApplication = KoinApplication.create() appDeclaration(koinApplication) return koinApplication } startKoin & koinApplication
33. @rbusarow fun startKoin(appDeclaration: KoinAppDeclaration): KoinApplication { val koinApplication = KoinApplication.create() GlobalContext.start(koinApplication) appDeclaration(koinApplication) koinApplication.createEagerInstances() return koinApplication } fun koinApplication(appDeclaration: KoinAppDeclaration): KoinApplication { val koinApplication = KoinApplication.create() appDeclaration(koinApplication) return koinApplication } startKoin & koinApplication
34. @rbusarow class MyApplication : Application() { override fun onCreate() { super.onCreate() Timber.plant(DebugTree()) } } MyApplication.kt
35. @rbusarow class MyApplication : Application() { override fun onCreate() { super.onCreate() Timber.plant(DebugTree()) startKoin { // route all Koin logs through android.util.Log androidLogger() } } } MyApplication.kt
36. @rbusarow private class TimberLogger(level: Level = Level.INFO) : Logger(level) { override fun log(level: Level, msg: MESSAGE) { if (this.level <= level) { when (this.level) { Level.DEBUG -> Timber.tag(KOIN_TAG).d(msg) Level.INFO -> Timber.tag(KOIN_TAG).i(msg) Level.ERROR -> Timber.tag(KOIN_TAG).e(msg) } } } } fun KoinApplication.timberLogger(level: Level = Level.INFO): KoinApplication { KoinApplication.logger = TimberLogger(level) return this } TimberLogger.kt
37. @rbusarow class MyApplication : Application() { override fun onCreate() { super.onCreate() Timber.plant(DebugTree()) startKoin { // route all Koin logs through Timber timberLogger() // provide Application context to the graph androidContext(this@MyApplication) } } } MyApplication.kt
38. @rbusarow class MyApplication : Application() { override fun onCreate() { super.onCreate() Timber.plant(DebugTree()) startKoin { // route all Koin logs through Timber timberLogger() // provide Application context to the graph androidContext(this@MyApplication) modules(koinDemoModules) } } } MyApplication.kt
39. @rbusarow Modules
40. @rbusarow val dataModule = module { } Modules
41. @rbusarow val dataModule = module { factory { } } Modules
42. @rbusarow val dataModule = module { factory { MyRepository() } } Modules
43. @rbusarow val dataModule = module { factory { Timber.v("Hello everyone!") MyRepository().also { Timber.v("Goodbye!") } } } Modules
44. @rbusarow val dataModule = module { factory { MyRepository() } } Modules
45. @rbusarow val dataModule = module { factory { MyRepository() } } Modules BeanDefinition Component
46. @rbusarow Connecting the Graph
47. class MyApplication : Application() { override fun onCreate() { super.onCreate() Timber.plant(DebugTree()) startKoin { // route all Koin logs through Timber timberLogger() // provide Application context to the graph androidContext(this@MyApplication) modules(koinDemoModules) } } } @rbusarow Connecting the Graph
48. class MyApplication : Application() { override fun onCreate() { super.onCreate() Timber.plant(DebugTree()) startKoin { // route all Koin logs through Timber timberLogger() // provide Application context to the graph androidContext(this@MyApplication) modules(koinDemoModules) } } } @rbusarow Connecting the Graph
49. @rbusarow val koinDemoModules: List<Module> get() = emptyListOf() val dataModule = module { factory { MyRepository() } } Modules
50. @rbusarow val koinDemoModules: List<Module> get() = listOf(dataModule) val dataModule = module { factory { MyRepository() } } Modules
51. @rbusarow class MyRepository { internal val database: MyDatabase = MyDatabase.init(APP_CONTEXT) internal val okHttpClient: OkHttpClient = OkHttpClient() internal val retrofit: Retrofit = Retrofit.Builder() .baseUrl("https://example.dev") .client(okHttpClient) .build() internal val service: MyService = retrofit.create<MyService>() internal val dao: MyDao = TODO() } Modules
52. @rbusarow class MyRepository( private val service: MyService, private val dao: MyDao ) { … } Modules
53. @rbusarow val dataModule = module { factory { MyRepository() } } Modules
54. @rbusarow val dataModule = module { factory { MyRepository(service = get(), dao = get()) } } Modules
55. @rbusarow val dataModule = module { factory<MyService> { TODO() } factory<MyDao> { TODO() } factory { MyRepository(service = get(), dao = get()) } } Modules
56. val dataModule = module { factory { OkHttpClient() } factory { Retrofit.Builder() .baseUrl("https://example.dev") .client(get<OkHttpClient>()) .build() } factory<MyService> { get<Retrofit>().create<MyService>() } factory<MyDao> { TODO() } factory { MyRepository(service = get(), dao = get()) } } @rbusarow Modules
57. val dataModule = module { factory { OkHttpClient() } factory { Retrofit.Builder() .baseUrl("https://example.dev") .client(get<OkHttpClient>()) .build() } factory<MyService> { get<Retrofit>().create<MyService>() } factory<MyDao> { TODO() } factory { MyRepository(service = get(), dao = get()) } } @rbusarow Modules
58. val dataModule = module { factory { OkHttpClient() } factory { Retrofit.Builder() .baseUrl("https://example.dev") .client(get<OkHttpClient>()) .build() } factory<MyService> { get<Retrofit>().create<MyService>() } factory { MyDatabase.init(androidApplication()) } factory<MyDao> { get<MyDatabase>().myDao } factory { MyRepository(service = get(), dao = get()) } } @rbusarow Modules
59. val dataModule = module { factory { OkHttpClient() } factory { Retrofit.Builder() .baseUrl("https://example.dev") .client(get<OkHttpClient>()) .build() } factory<MyService> { get<Retrofit>().create<MyService>() } factory { MyDatabase.init(androidApplication()) } factory<MyDao> { get<MyDatabase>().myDao } factory { MyRepository(service = get(), dao = get()) } } @rbusarow Modules
60. val dataModule = module { factory { OkHttpClient() } factory { Retrofit.Builder() .baseUrl("https://example.dev") .client(get<OkHttpClient>()) .build() } factory<MyService> { get<Retrofit>().create<MyService>() } factory { MyDatabase.init(androidApplication()) } factory<MyDao> { get<MyDatabase>().myDao } factory { MyRepository(service = get(), dao = get()) } } @rbusarow Modules
61. val dataModule = module { factory { OkHttpClient() } factory { Retrofit.Builder() .baseUrl("https://example.dev") .client(get<OkHttpClient>()) .build() } factory<MyService> { get<Retrofit>().create<MyService>() } factory { MyDatabase.init(androidApplication()) } factory<MyDao> { get<MyDatabase>().myDao } factory { MyRepository(service = get(), dao = get()) } } @rbusarow Modules
62. val dataModule = module { factory<OkHttpClient> { OkHttpClient() } factory<Retrofit> { Retrofit.Builder() .baseUrl("https://example.dev") .client(get<OkHttpClient>()) .build() } factory<MyService> { get<Retrofit>().create<MyService>() } factory<MyDatabase> { MyDatabase.init(androidApplication()) } factory<MyDao> { get<MyDatabase>().myDao } factory<MyRepository> { MyRepository(service = get(), dao = get()) } } @rbusarow Modules
63. val dataModule = module { factory<OkHttpClient> { OkHttpClient() } factory<Retrofit> { Retrofit.Builder() .baseUrl("https://example.dev") .client(get<OkHttpClient>()) .build() } factory<MyService> { get<Retrofit>().create<MyService>() } factory<MyDatabase> { MyDatabase.init(androidApplication()) } factory<MyDao> { get<MyDatabase>().myDao } factory<MyRepository> { MyRepository(service = get(), dao = get()) } } @rbusarow Modules
64. val dataModule = module { single<OkHttpClient> { OkHttpClient() } single<Retrofit> { Retrofit.Builder() .baseUrl("https://example.dev") .client(get<OkHttpClient>()) .build() } single<MyService> { get<Retrofit>().create<MyService>() } single<MyDatabase> { MyDatabase.init(androidApplication()) } factory<MyDao> { get<MyDatabase>().myDao } single<MyRepository> { MyRepository(service = get(), dao = get()) } } @rbusarow Modules
65. @rbusarow Accessing the Graph
66. @rbusarow class MyScreen { val repository: MyRepository = TODO() } Accessing the Graph
67. @rbusarow class MyScreen { val repository = GlobalContext.get().koin.get<MyRepository>() } Accessing the Graph
68. @rbusarow class MyScreen : KoinComponent { val repository = get<MyRepository>() } Accessing the Graph
69. @rbusarow class MyScreen : Fragment() { val repository = get<MyRepository>() } Accessing the Graph
70. @rbusarow class MyScreen : Fragment() { val repository = get<MyRepository>() } class MyViewModel(private val repository: MyRepository) : ViewModel() { } Accessing the Graph
71. @rbusarow val koinDemoModules: List<Module> get() = listOf(dataModule) val viewModelModule = module { viewModel<MyViewModel> { MyViewModel(repository = get()) } } Accessing the Graph
72. @rbusarow val koinDemoModules: List<Module> get() = listOf(dataModule, viewModelModule) val viewModelModule = module { viewModel<MyViewModel> { MyViewModel(repository = get()) } } Accessing the Graph
73. @rbusarow class MyScreen : Fragment() { val viewModel = get<MyViewModel>() } class MyViewModel(private val repository: MyRepository) : ViewModel() { } Accessing the Graph
74. @rbusarow class MyScreen : Fragment() { val viewModel by viewModel<MyViewModel>() } class MyViewModel(private val repository: MyRepository) : ViewModel() { } Accessing the Graph
75. @rbusarow class MyScreen : Fragment() { val repository by inject<MyRepository>() val viewModel by viewModel<MyViewModel>() } class MyViewModel(private val repository: MyRepository) : ViewModel() { } Accessing the Graph
76. @rbusarow Parameters
77. @rbusarow class MyScreen : Fragment() { val repository by inject<MyRepository>() val viewModel by viewModel<MyViewModel>() } class MyViewModel(private val repository: MyRepository) : ViewModel() { } Parameters
78. @rbusarow class MyScreen : Fragment() { val repository by inject<MyRepository>() val viewModel by viewModel<MyViewModel>() } class MyViewModel( private val userId: Int, private val repository: MyRepository ) : ViewModel() Parameters
79. @rbusarow class MyScreen : Fragment() { val repository by inject<MyRepository>() val viewModel by viewModel<MyViewModel>() } class MyViewModel( private val userId: Int, private val repository: MyRepository ) : ViewModel() val viewModelModule = module { viewModel<MyViewModel> { (userId: Int) -> MyViewModel(userId = userId, repository = get()) } } Parameters
80. @rbusarow class MyScreen : Fragment() { val repository by inject<MyRepository>() val viewModel by viewModel<MyViewModel> { parametersOf(123) } } class MyViewModel( private val userId: Int, private val repository: MyRepository ) : ViewModel() val viewModelModule = module { viewModel<MyViewModel> { (userId: Int) -> MyViewModel(userId = userId, repository = get()) } } Parameters
81. @rbusarow Scope
82. @rbusarow val koinDemoModules: List<Module> get() = listOf(dataModule, scopedModule, viewModelModule) val scopedModule = module { scope(scopeName = named("login")) { scoped { Preferences() } } } Scope
83. @rbusarow val koinDemoModules: List<Module> get() = listOf(dataModule, scopedModule, viewModelModule) val scopedModule = module { scope(scopeName = named("login")) { scoped { Preferences() } } } Scope
84. @rbusarow val koinDemoModules: List<Module> get() = listOf(dataModule, scopedModule, viewModelModule) val scopedModule = module { scope(scopeName = named("login")) { scoped { Preferences() } } } class Anywhere : KoinComponent { val userID = 153 val loginScope = getKoin().createScope(userID.toString(), named("login")) val preferences by loginScope.inject<Preferences>() } Scope
85. @rbusarow class MyScreen : Fragment() { val presenter by currentScope.inject<Presenter>() val viewModel by viewModel<MyViewModel>() } val scopedModule = module { scope(named<MyScreen>()) { scoped { Presenter() } } scope(scopeName = named("login")) { scoped { Preferences() } } } Parameters
86. @rbusarow Dynamic Features
87. @rbusarow val featureModules = listOf(scopedModule, viewModelModule) Dynamic Features
88. @rbusarow val featureModules = listOf(scopedModule, viewModelModule) private val loadFeature by lazy { loadKoinModules(featureModules) } Dynamic Features
89. @rbusarow val featureModules = listOf(scopedModule, viewModelModule) private val loadFeature by lazy { loadKoinModules(featureModules) } fun initModules() = loadFeature Dynamic Features
90. @rbusarow val featureModules = listOf(scopedModule, viewModelModule) private val loadFeature by lazy { loadKoinModules(featureModules) } fun initModules() = loadFeature class SomeFeatureActivity : Activity() { init { initModules() } } Dynamic Features
91. @rbusarow Testing
92. @rbusarow val koinDemoModules: List<Module> get() = listOf(dataModule, scopedModule, viewModelModule) Testing
93. @rbusarow internal class ModuleTest : KoinTest { @BeforeEach fun beforeEach() { startKoin { modules(koinDemoModules) } } @AfterEach fun afterEach() { getKoin().close() } @Test fun `check modules`() { getKoin().checkModules() } } Testing
94. @rbusarow internal class RepositoryTest : KoinTest { val mockModule = module { single<MyDao>(override = true) { MockDao() } } @Test fun `MyRepository should return Dao contents`() { loadKoinModules(mockModule) val repo = get<MyRepository>() // repo is now using mocked Dao } } Testing
95. @rbusarow Further Reading http://bit.ly/322XZr5 http://bit.ly/2L2IfO4 Koin Android documentation: Koin Core documentation: Koin Github: http://bit.ly/2ZkTk2d
96. rbusarow rbusarow rbusarow THANKS! Rick Busarow rickbusarow@gmail.com
97. @rbusarow Questions?