@Inject Basics

Dependency Injection is a concept which has become quite popular among Android developers as our applications break barriers on features and at the same time project complexity increases. It is also a heavily researched topic by developers with 20k questions on stack overflow(2k+ for dagger).
While most projects use dagger as a de-facto framework for Android, this talk would be more focussed on understanding concepts of DI and applying the same without a framework. We’ll go through concepts of supplying dependencies, various types of injection and understanding inversion of control. All of this without using a framework, with raw code in Kotlin and an actual android app with real life problems around networking, storage and threading.
We’ll then dig deep in how libraries like Dagger, Koin etc operate to provide the same with code generation or reflection.

Transcript

1. @Inject Basics ! Jitin Sharma GO-JEK @_jitinsharma
2. Dagger!
4. @Provides @Inject @Module @Component @Named @Singleton @Qaulifier @BindsInstance HasActivityInjector AndroidInjection @Subcomponent @ContributesAndroidInjector
7. Dependency Injection What and Why @_jitinsharma
8. Dependency injection is a technique whereby one object supplies the dependencies of another object
9. Setter Injection class Jitin { lateinit var stage: Stage fun setStage(stage: Stage) { this.stage = stage } ...
10. Constructor Injection class Jitin(private val stage: Stage) { ...
11. Constructor Injection class Jitin(private val stage: Stage, private var mic: Boolean = true) Jitin(stage = getStage(), mic = false) Jitin(stage = getStage())
12. Android Components - Activity - Application - Services - ...
13. INVERSIOИ OF CONTROL @_jitinsharma
14. DogActivity DogPresenter DogAPI DogRepository DogView
15. DogActivity DogPresenter DogAPI DogRepository DogView Dependencies
16. DogActivity DogPresenter DogAPI DogRepository DogView Dependencies
17. Dependency Container val dogApi: DogApi get() = ApiClient.dogClient.create(DogApi::class.java) val dogRepository get() = DogRepository() val presenter get() = DogPresenter()
18. Dependency Container object DogDependencyContainer { var dogView: DogView? = null fun init(dogView: DogView) { this.dogView = dogView } ... val dogApi: DogApi get() = ApiClient.dogClient.create(DogApi::class.java) val dogRepository get() = DogRepository() val presenter get() = DogPresenter()
19. Dependency Container inline fun <reified T> inject(): T { return when (T::class) { DogApi::class -> dogApi as T DogPresenter::class -> presenter as T DogRepository::class -> dogRepository as T DogView::class -> dogView as T else -> throw DependencyNotFoundException() } }
20. Dependency Container class DogPresenter { private val dogView by lazy { inject<DogView>() } private val dogRepository by lazy { inject<DogRepository>() } class DogRepository { private val dogApi by lazy { inject<DogApi>() }
21. Dependency Container class DogActivity : AppCompatActivity(), DogView { private val dogPresenter by lazy { inject<DogPresenter>() } ... override fun onCreate(savedInstanceState: Bundle?) { ... DogDependencyContainer.init(this) ...
22. SERVICE LOCATOR @_jitinsharma
23. DogActivity DogPresenter DogAPI DogRepository DogView DependencyContainer
24. DogActivity DogPresenter DogAPI DogRepository DogView class DogRepository(private val dogApi: DogApi) class DogPresenter(private var dogView: DogView?, private val dogRepository: DogRepository) // Interface DependencyContainer
25. Dependency Container private val dogApi get() = ApiClient.dogClient.create(DogApi::class.java) private val dogRepository get() = DogRepository(dogApi) val presenter get() = DogPresenter(dogView, dogRepository)
26. Dependency Container class DogActivity : AppCompatActivity(), DogView { private val dogPresenter by lazy { inject<DogPresenter>() } ... override fun onCreate(savedInstanceState: Bundle?) { ... DogDependencyContainer.init(this) ...
29. DAGGER @_jitinsharma
30. @Inject javax.inject (JSR 330)
31. @Inject javax.inject (JSR 330) @Provides @Provides ...
32. @Inject javax.inject (JSR 330) @Provides @Provides ... @Module
33. @Inject javax.inject (JSR 330) @Provides @Provides ... @Module @Component
34. DogActivity DogPresenter DogAPI DogRepository DogView @Provides fun dogView(): DogView = dogView @Provides fun dogApi(): DogApi = ApiClient.dogClient.create(DogApi::class.java)
35. class DogRepository @Inject constructor(private val dogApi: DogApi) class DogPresenter @Inject constructor( private var dogView: DogView?, private val dogRepository: DogRepository ) Injecting Constructors
36. @Component(modules = [DogModule::class]) interface DogComponent { fun inject(mainActivity: MainActivity) } Wiring up dependencies
37. Injecting Dependencies class MainActivity : AppCompatActivity(), DogView { @Inject lateinit var dogPresenter: DogPresenter override fun onCreate(savedInstanceState: Bundle?) { DaggerDogComponent.builder().dogModule(DogModule((this))).build().inject(this) } }
38. public final class DaggerDogComponent implements DogComponent { private DogRepository getDogRepository() { return new DogRepository(DogModule_DogApiFactory.dogApi(dogModule)); } private DogPresenter getDogPresenter() { return new DogPresenter(DogModule_DogViewFactory.dogView(dogModule), getDogRepository()); } ... Component Generation
39. Injection via code generation DaggerDogComponent... ..inject(this) DogActivity DogActivity.kt
40. Injection via code generation DaggerDogComponent... ..inject(this) DogActivity @Override public void inject(DogActivity dogActivity) { injectDogActivity(dogActivity); } DogActivity.kt DaggerCatComponent.java
41. Injection via code generation DaggerDogComponent... ..inject(this) DogActivity @Override public void inject(DogActivity dogActivity) { injectDogActivity(dogActivity); } public static void injectDogPresenter(DogActivity instance, DogPresenter dogPresenter) { instance.dogPresenter = dogPresenter; } DogActivity.kt DaggerCatComponent.java DogActivity_MembersInjector.java
42. Injection via code generation DaggerDogComponent... ..inject(this) DogActivity @Override public void inject(DogActivity dogActivity) { injectDogActivity(dogActivity); } public static void injectDogPresenter(DogActivity instance, DogPresenter dogPresenter) { instance.dogPresenter = dogPresenter; } @Inject lateinit var dogPresenter: DogPresenter DogActivity.kt DaggerCatComponent.java DogActivity_MembersInjector.java
43. Scopes @Singleton @Component(modules = [AppModule::class]) interface AppComponent { ... @DogScope @Component(modules = [DogModule::class], dependencies = [AppComponent::class]) interface DogComponent { ... DogComponent.kt AppComponent.kt
44. DaggerDogComponent.builder() .appComponent(appComponent) .dogModule(DogModule((this))) .build() .inject(this) Inversion of Control
45. DAGGER-ANDROID @_jitinsharma
46. “screams in japanese”
47. “screams in japanese”
48. AndroidInjector Activity Fragment Service BrodcastReceiver ContentProvider Core Components
49. @Module class DogModule { @Provides fun providesDogView(dogActivity: DogActivity): DogView = dogActivity ... @Binds abstract fun provideDogView(dogActivity: DogActivity): DogView
50. @Module abstract class BuildersModule { @ContributesAndroidInjector(modules = [DogModule::class]) abstract fun bindDogActivity(): DogActivity ...
51. @Singleton @Component(modules = [AndroidInjectionModule::class, AppModule::class, BuildersModule::class]) interface AppComponent { @Component.Builder interface Builder { @BindsInstance fun application(application: AnimalApp): Builder fun build(): AppComponent } fun inject(app: AnimalApp)
52. class DogActivity : AppCompatActivity(), DogView { @Inject lateinit var dogPresenter: DogPresenter ... override fun onCreate(savedInstanceState: Bundle?) { AndroidInjection.inject(this) ...
53. AndroidInjection.inject(this) Activity Fragment Service Content Provider Broadcast Receiver
54. Application Activity Fragment Service Content Provider Broadcast Receiver HasActivityInjector HasFragmentInjector HasServiceInjector HasBroadcastReceiverInjector HasContentProviderInjector HasFragmentInjector
55. Application Activity Fragment Service Content Provider Broadcast Receiver HasActivityInjector HasFragmentInjector HasServiceInjector HasBroadcastReceiverInjector HasContentProviderInjector HasFragmentInjector
56. class AnimalApp : Application(), HasActivityInjector { @Inject lateinit var dispatchingAndroidInjector: DispatchingAndroidInjector<Activity> override fun activityInjector(): AndroidInjector<Activity> = dispatchingAndroidInjector override fun onCreate() { super.onCreate() DaggerAppComponent.builder() .application(this) .build() .inject(this) ...
57. class AnimalApp : Application(), HasActivityInjector { @Inject lateinit var dispatchingAndroidInjector: DispatchingAndroidInjector<Activity> override fun activityInjector(): AndroidInjector<Activity> = dispatchingAndroidInjector override fun onCreate() { super.onCreate() DaggerAppComponent.builder() .application(this) .build() .inject(this) ...
58. class AnimalApp : Application(), HasActivityInjector { @Inject lateinit var dispatchingAndroidInjector: DispatchingAndroidInjector<Activity> override fun activityInjector(): AndroidInjector<Activity> = dispatchingAndroidInjector override fun onCreate() { super.onCreate() DaggerAppComponent.builder() .application(this) .build() .inject(this) ...
59. AppComponent Activity Modules Builder Module (@ContributesAndroidInjector) //Generated DaggerAppComponent SubComponent: AndroidInjector<> Provider Map<Class, Provider> DispatchingAndroidInjector
60. //Generated DaggerAppComponent SubComponent: AndroidInjector<> Provider Map<Class, Provider> DispatchingAndroidInjector @Inject dispatchingAndroidInjector: DispatchingAndroidInjector<Activity> Application class Activity Class AndroidInjection.inject(this) @Override public void inject(DogActivity arg0) { injectDogActivity(arg0); }
61. class DogActivity : DaggerAppCompatActivity(), DogView { @Inject lateinit var dogPresenter: DogPresenter ... Support Module
63. KOTLIN @_jitinsharma
64. Kotlin Delegation Lambda DSL
65. KOIN @_jitinsharma
66. • A Dependency Injection Framework for Kotlin • Does not use code generation • Works using Lambdas and Extensions KOIN
67. val catModule = module { single<CatApi> { ApiClient.catClient.create(CatApi::class.java) } single { CatRepository(get()) } factory { (catView: CatView) -> CatPresenter(catView, get()) } } Module Declaration
68. val catModule = module { single<CatApi> { ApiClient.catClient.create(CatApi::class.java) } single { CatRepository(get()) } factory { (catView: CatView) -> CatPresenter(catView, get()) } } Module Declaration
69. Startup Configuration class AnimalApp : Application(){ override fun onCreate() { super.onCreate() startKoin { androidContext(this@AnimalApp) modules(listOf(catModule, dogModule, appModule)) } ...
70. class CatActivity : AppCompatActivity(), CatView { private val catPresenter: CatPresenter by inject { parametersOf(this) } private val imageLoader: ImageLoader by inject() ... Injecting Members
71. Load Modules BeanRegistry HashSet by inject()
72. Load Modules BeanRegistry HashSet by inject() Service Locator
73. Modules and Scopes unloadKoinModules(catModule) loadKoinModules(catModule) // GlobalScope
74. Modules and Scopes scope(named<CatActivity>()) { scoped { (catView: CatView) -> CatPresenter(catView, get()) } } CatPresenter by currentScope.inject { ... LifeCycleOwner
75. Modules and Scopes scope(named<CatActivity>()) { scoped { (catView: CatView) -> CatPresenter(catView, get()) } } CatPresenter by currentScope.inject { ... LifeCycleOwner
76. Koin has • Easy configuration • Drop in support for Android with ViewModels and Scopes • Excellent documentation and testing support
77. Koin does not have • Strict Compile time safety • Facility of automatic constructors without using reflection
78. Probably Yes Do you need Dependency Injection
79. It Depends Do you need DI frameworks?
80. Before software can be reusable it first has to be usable. Ralph Johnson
81. - Koin - Kodein - Katana … … - RoboGuice - Dagger 1 - Dagger 2 Kotlin
82. • https://jakewharton.com/helping-dagger-help-you/ • https://github.com/handstandsam/ShoppingApp Resources
83. Danke schön @_jitinsharma