Dependency Injection with Koin

While Dagger has been the go to library for DI in Android, in this talk we explore Koin (which recently hit 2.0) and see whether it can be a viable alternative for you and how it compares with Dagger.

1. DEPENDENCY INJECTION WITH KOIN Shashank Mishra @SHKM9 .droidconGreece19
2. why • complexity
 • build times
 • Kotlin
 • multiplatform P
3. modules @Module class AppModule { @Provides @Singleton fun providePreferences(application: Application): SharedPreferences { return PreferenceManager.getDefaultSharedPreferences(application) }
 
 @Provides @Singleton fun provideUserPostsUseCase(repository: UserRepository): UsersPostsUseCase { return UsersPostsUseCase(repository) }
 }
4. modules @Module class AppModule { @Provides @Singleton fun providePreferences(application: Application): SharedPreferences { return PreferenceManager.getDefaultSharedPreferences(application) }
 
 @Provides @Singleton fun provideUserPostsUseCase(repository: UserRepository): UsersPostsUseCase { return UsersPostsUseCase(repository) }
 }
5. modules val appModule = module { 
 
 
 
 
 
 
 } single { createSharedPreferences(context = get()) } 
 factory { UsersPostsUseCase(prefs = get()) } 
 viewModel { UserProfileViewModel(userPostsUseCase = get()) }
6. component @Singleton @Component(modules = [AppModule"::class]) interface AppComponent { fun inject(activity: MainActivity) @Component.Builder interface Builder { @BindsInstance fun application(application: Application): Builder fun build(): AppComponent } }
7. component @Singleton @Component(modules = [AppModule"::class]) interface AppComponent { fun inject(activity: MainActivity) @Component.Builder interface Builder { @BindsInstance fun application(application: Application): Builder fun build(): AppComponent } }
8. component @Singleton @Component(modules = [AppModule"::class]) interface AppComponent { fun inject(activity: MainActivity) @Component.Builder interface Builder { @BindsInstance fun application(application: Application): Builder fun build(): AppComponent } }
9. component val component: AppComponent by lazy { DaggerAppComponent.builder().application(this).build() }
10. startKoin { androidContext(this@MyApplication) modules(listOf(appModule, networkModule, cacheModule)) } component
11. class UserPrefs @Inject constructor(private val prefs: SharedPreferences) clients
12. class ProfileFragment : Fragment() {
 @Inject lateinit var sharedPreferences: SharedPreferences . . . override fun onCreate(savedInstanceState: Bundle?) { component.inject(this) } } clients
13. class ProfileFragment : Fragment() { private val sharedPreferences by inject<SharedPreferences>() private val viewModel: ProfileViewModel by viewModel() . . .
 
 } class UserPrefs(private val sharedPreferences: SharedPreferences) clients
14. val appModule = module { single { (id: String) !-> SomeUseCase(id) }
 } parameters
15. val appModule = module { single { (id: String) !-> SomeUseCase(id) }
 private val useCase: SomeUseCase by inject { parametersOf(getIntentData()) } } parameters
16. multi-binding @Binds @IntoMap @ClassKey(Square"::class) abstract fun provideSquare(shape: Square): Shape @Binds @IntoMap @ClassKey(Triangle"::class) abstract fun provideTriangle(shape: Triangle): Shape
17. multi-binding @Binds @IntoMap @ClassKey(Square"::class) abstract fun provideSquare(shape: Square): Shape @Binds @IntoMap @ClassKey(Triangle"::class) abstract fun provideTriangle(shape: Triangle): Shape
18. multi-binding @Binds @IntoMap @ClassKey(Square"::class) abstract fun provideSquare(shape: Square): Shape @Binds @IntoMap @ClassKey(Triangle"::class) abstract fun provideTriangle(shape: Triangle): Shape
19. multi-binding @Binds @IntoMap @ClassKey(Square"::class) abstract fun provideSquare(shape: Square): Shape @Binds @IntoMap @ClassKey(Triangle"::class) abstract fun provideTriangle(shape: Triangle): Shape
20. multi-binding val shapes = component.shapesMap() interface Component { fun shapesMap(): Map<Class!!<*>, Shape> }
21. multi-binding val userModule = module { single { Square() } bind Shape"::class single { Triangle() } bind Shape"::class }
22. multi-binding val userModule = module { single { Square() } bind Shape"::class single { Triangle() } bind Shape"::class } val shape: Shape = bind<Shape, Square>()
23. scopes
24. scopes @PerFragment @Subcomponent(modules = [ProfileModule"::class]) interface ProfileComponent { 
 fun inject(fragment: ProfileFragment) @Subcomponent.Builder interface Builder { fun build(): ProfileComponent } }
25. scopes @PerFragment @Subcomponent(modules = [ProfileModule"::class]) interface ProfileComponent { 
 fun inject(fragment: ProfileFragment) @Subcomponent.Builder interface Builder { fun build(): ProfileComponent } }
26. scopes @PerFragment @Subcomponent(modules = [ProfileModule"::class]) interface ProfileComponent { fun inject(fragment: ProfileFragment) @Subcomponent.Builder interface Builder { fun build(): ProfileComponent } }
27. scopes @PerFragment @Subcomponent(modules = [ProfileModule"::class]) interface ProfileComponent { fun inject(fragment: ProfileFragment) @Subcomponent.Builder interface Builder { fun build(): ProfileComponent } }
28. scopes @Singleton @Component(modules = [AppModule"::class]) interface AppComponent {
 
 . . . 
 val profileComponentBuilder: ProfileComponent.Builder }
29. scopes class ProfileFragment : Fragment() { 
 @Inject lateinit var sharedPreferences: SharedPreferences override fun onCreate(savedInstanceState: Bundle?) { 
 appComponent.profileComponentBuilder.build().inject(this) 
 } }
30. scopes module {
 scope(named<ProfileFragment>()) { scoped { UsersPostsUseCase(userRepository = get()) } }
 }
31. scopes class ProfileFragment : Fragment() { private val usersPostsUseCase: UsersPostsUseCase by inject() . . . 
 }
32. scopes class ProfileFragment : Fragment() { private val usersPostsUseCase: UsersPostsUseCase by currentScope.inject() . . . 
 }
33. scopes module {
 scope(named<ProfileFragment>()) { scoped { UsersPostsUseCase(userRepository = get()) } }
 }
34. scopes module {
 scope(named(DEMO_SCOPE)) { scoped { UsersPostsUseCase(userRepository = get()) } }
 }
35. scopes private val scope: Scope by lazy { val customScope = getKoin().createScope(SCOPE_ID, named(DEMO_SCOPE)) customScope }
36. scopes private val usersPostsUseCase: UsersPostsUseCase by scope.inject()
37. scopes private val usersPostsUseCase: UsersPostsUseCase by scope.inject() scope.close()
38. scopes fun LifecycleOwner.bindScope(scope: Scope, event: Lifecycle.Event = Lifecycle.Event.ON_DESTROY) { lifecycle.addObserver(ScopeObserver(event, this, scope)) }
39. multi-module Core Feature 1 Feature 2
40. multi-module Core Feature Feature @Component(modules = [CoreModule"::class]) @Singleton interface CoreComponent { fun provideGson(): Gson }
41. multi-module Core Feature Feature @Component(modules = [CoreModule"::class]) @Singleton interface CoreComponent { fun provideGson(): Gson }
42. multi-module @Component(modules = [CoreModule"::class]) @Singleton interface CoreComponent { fun provideGson(): Gson } @FeatureScope @Component( modules = [FeatureModule"::class], dependencies = [CoreComponent"::class] ) interface FeatureComponent { @Component.Builder interface Builder { fun build(): FeatureComponent fun coreComponent(coreComponent: CoreComponent): Builder } } Core Feature Feature
43. multi-module @Component(modules = [CoreModule"::class]) @Singleton interface CoreComponent { fun provideGson(): Gson } @FeatureScope @Component( modules = [FeatureModule"::class], dependencies = [CoreComponent"::class] ) interface FeatureComponent { @Component.Builder interface Builder { fun build(): FeatureComponent fun coreComponent(coreComponent: CoreComponent): Builder } } Core Feature Feature
44. multi-module @Component(modules = [CoreModule"::class]) @Singleton interface CoreComponent { fun provideGson(): Gson } @FeatureScope @Component( modules = [FeatureModule"::class], dependencies = [CoreComponent"::class] ) interface FeatureComponent { @Component.Builder interface Builder { fun build(): FeatureComponent fun coreComponent(coreComponent: CoreComponent): Builder } } Core Feature Feature
45. multi-module val coreComponent = DaggerCoreComponent.builder().build() 
 . . . val featureComponent = DaggerFeatureComponent.builder() .coreComponent(coreComponent).build().inject(this)
46. multi-module startKoin { androidContext(this@MyApplication) modules(listOf(appModule, networkModule, cacheModule)) } }
47. multi-module startKoin { androidContext(this@MyApplication) modules(listOf(coreModule)) } }
48. multi-module loadKoinModules(listOf(featureModule1, featureModule2))
49. multi-module unloadKoinModules(listOf(featureModule1))
50. testing
51. testing startKoin { androidContext(application) modules(listOf(appModule)) }.checkModules()
52. testing
53. testing class UserService(private val repo: UserRepository)
54. testing class UserServiceTest : KoinTest { private val service: UserService by inject() @Before fun before() { startKoin { modules(listOf(userModule)) } } } class UserService(private val repo: UserRepository)
55. testing class UserServiceTest : KoinTest { private val service: UserService by inject() @Before fun before() { startKoin { modules(listOf(userModule)) } } } class UserService(private val repo: UserRepository)
56. testing class UserServiceTest : KoinTest { private val service: UserService by inject() @Before fun before() { startKoin { modules(listOf(userModule)) } } } class UserService(private val repo: UserRepository)
57. testing @Test fun `test getting user repo`() { declareMock<UserRepository> { whenever(getRepoId()) doReturn "1" } val result = service.getUserRepo()
 assert(. . .) } class UserService(private val repo: UserRepository)
58. performance https://github.com/Sloy/android-dependency-injection-performance DAGGER KOIN Nexus 6 0.3ms 19.8ms OnePlus 5 0.0ms 2.3ms OnePlus 1 0.0ms 11.84ms Mi A1 0.02ms 9.17ms Galaxy S8 0.01ms 5.68ms Setup Times
59. performance https://github.com/Sloy/android-dependency-injection-performance Methods Fields Classes Percentage 17.5 35 52.5 70 8.29 35.1 62.47 8.33 32.44 57.31 Koin Dagger
60. class ProfileViewModel @Inject constructor( private val profileService: ProfileService, private val errorHandler: ErrorHandler )
61. class ProfileViewModel @Inject constructor( private val profileService: ProfileService, private val authService: AuthService, private val errorHandler: ErrorHandler )
62. module { viewModel { ProfileViewModel(get()) } }
63. module { viewModel { ProfileViewModel(get(), get()) } }
64. module { viewModel { ProfileViewModel(get(), get(), get()) } }
66. DAGGER KOIN Automatic injection at the hands of compile-time code generator Manual injection using a bunch of lambdas for every type
67. module { viewModel<ProfileViewModel>() }
68. module { viewModel<ProfileViewModel>() single<UserRepository>() }
69. module { viewModel<ProfileViewModel>() single<UserRepository>()
 factory<UsersPostsUseCase>() }
70. inline fun <reified T : Any> create(context: Scope): T { val kClass = T"::class lateinit var instance: T val ctor = kClass.getFirstJavaConstructor() val args = getArguments(ctor, context) instance = ctor.makeInstance(args) return instance }
71. compile time safety
72. Is Koin really DI?
73. With service locator the application class asks for it explicitly by a message to the locator. With injection there is no explicit request. - Martin Fowler
74. class ProfileFragment : Fragment() { private val sharedPreferences by inject<SharedPreferences>()
 }
75. class ProfileFragment : Fragment() {
 @Inject lateinit var sharedPreferences: SharedPreferences . . . override fun onCreate(savedInstanceState: Bundle?) { component.inject(this) } }
76. component.inject(this) private val sharedPreferences by inject<SharedPreferences>() VS
77. class ProfileFragment : Fragment() {
 @Inject lateinit var sharedPreferences: SharedPreferences . . . override fun onCreate(savedInstanceState: Bundle?) { component.inject(this) } }
78. val fragment = ProfileFragment() component.inject(fragment)
79. recap DAGGER ✓ Compile time safety
 ✓ Scales really well
 ✓ Ideal for large projects
 x Complexity
 x Build times KOIN ✓ Easy to learn
 ✓ Quick build times
 ✓ Ideal for mid sized projects
 x Breaks at runtime
 x Manual graph maintenance
 x Scales poorly
80. THANK YOU! QUESTIONS?
81. fueled.com/jobs