Hilt the DI ground running

This talk was about Dependency Injection with Hilt at DevFest Egypt. First I explained the concept of Dependency Injection without libraries. Next, I showed how to incorporate Hilt into a new app and how to migrate an existing app.

1. Hilt the DI ground running Moyinoluwa Adeyemi @moyheen
2. What is Dependency Injection?
3. What is Dependency Injection? “dependency injection is a technique in which an object receives other objects that it depends on” According to good ol’ wikipedia
4. Dependency Injection
5. Dependency Injection
6. No Dependency Injection class RoboGardener { fun waterPlant() { val waterSource = WaterSource() waterSource.dispenseWater() } }
7. Dependency Injection - Constructor class RoboGardener(private val waterSource: WaterSource) { fun waterPlant() { waterSource.dispenseWater() } }
8. Dependency Injection - Constructor class RoboGardener(private val waterSource: WaterSource) { fun waterPlant() { waterSource.dispenseWater() } } fun main() { val roboGardener = RoboGardener(CupOfWater()) roboGardener.waterPlant() }
9. Dependency Injection - Setter class RoboGardener { lateinit var waterSource: WaterSource fun waterPlant() { waterSource.dispenseWater() } }
10. Dependency Injection - Setter class RoboGardener { lateinit var waterSource: WaterSource fun waterPlant() { waterSource.dispenseWater() } } fun main() { val roboGardener = RoboGardener() roboGardener.waterSource = WateringCan() roboGardener.waterPlant() }
11. Dependency Injection - Interface interface WaterSourceManager { fun provideWaterSource(waterSource: WaterSource) }
12. Dependency Injection - Interface interface WaterSourceManager { fun provideWaterSource(waterSource: WaterSource) } class RoboGardener() : WaterSourceManager { private lateinit var waterSource: WaterSource override fun provideWaterSource(waterSource: WaterSource) { this.waterSource = waterSource } ...
13. Dependency Injection - Interface interface WaterSourceManager { fun provideWaterSource(waterSource: WaterSource) } class RoboGardener() : WaterSourceManager { private lateinit var waterSource: WaterSource override fun provideWaterSource(waterSource: WaterSource) { this.waterSource = waterSource } fun waterPlant() { waterSource.dispenseWater() } } fun main() { val roboGardener = RoboGardener() roboGardener.provideWaterSource(Hose()) roboGardener.waterPlant() }
14. RoboGardener WaterSource Dependency Injection - Graph
15. Service Locators
16. Service Locators class RoboGardener { fun waterPlant() { val waterSource = CupOfWater() waterSource.dispenseWater() } }
17. class RoboGardener { fun waterPlant() { val waterSource = ServiceLocator.getInstance.findWaterSource() waterSource.dispenseWater() } } Service Locators
18. No increase in app size Manual Dependency Injection
19. Manual Dependency Injection No increase in app size Low Learning Curve
20. High maintenance costs Manual Dependency Injection Low Learning Curve No increase in app size ♀
21. Dependency Injection - Dagger Dagger Code generation Steep learning curve For Java or Kotlin developers Useful for large projects
22. Dependency Injection - Hilt What is different?
23. Dependency Injection - Hilt Low Learning Curve
24. Dependency Injection - Hilt Low Learning Curve Free Lifecycle Management ♻
25. Dependency Injection - Hilt Low Learning Curve Free Lifecycle Management ♻ Co-exist with Dagger ♂
26. Dependency Injection - Hilt Usage - Annotations
27. @HiltAndroidApp class HiltSampleApplication : Application() @HiltAndroidApp
28. @AndroidEntryPoint class MainActivity : AppCompatActivity() { @Inject lateinit var imageLoader: ImageLoader private val viewModel: HiltSampleViewModel by viewModels() ... @AndroidEntryPoint
29. Activity imageLoader viewModel @AndroidEntryPoint
30. @Module @InstallIn(ApplicationComponent::class) abstract class AppModule @InstallIn
31. @Module @InstallIn(ApplicationComponent::class) abstract class AppModule { @Binds abstract fun bindImageLoader(imageLoader: GlideImageLoader): ImageLoader ... } @InstallIn
32. @Module @InstallIn(ApplicationComponent::class) object NetworkModule { @Provides fun providesMoshi(): Moshi = Moshi.Builder() .build() ... @InstallIn
33. class HiltSampleViewModel @ViewModelInject constructor( private val hiltSampleRepository: HiltSampleRepository ) : ViewModel() { ... ViewModels - @ViewModelInject
34. ViewModel repository ViewModels - @ViewModelInject Activity imageLoader viewModel
35. @AndroidEntryPoint @AndroidEntryPoint class MainActivity : AppCompatActivity() { @Inject lateinit var imageLoader: ImageLoader private val viewModel: HiltSampleViewModel by viewModels() ...
36. @EntryPoint - Interface @EntryPoint @InstallIn(ApplicationComponent::class) interface ImageFeatureModule { fun imageLoader(): ImageLoader }
37. @EntryPoint - Dependency retrieval val imageLoader = EntryPoints .get(applicationContext, ImageFeatureModule::class.java) .imageLoader()
38. @EntryPoint - Interface retrieval EntryPointAccessors.fromApplication( applicationContext, ImageFeatureModule::class.java )
39. Dependency Injection - Hilt Usage - Scoping
40. https://developer.android.com/training/dependency-injection/hilt-android#component-scopes Scoping
41. https://dagger.dev/hilt/component-hierarchy.svg Scoping - Hierarchy
42. Scoping - Unscoped bindings @Module @InstallIn(ApplicationComponent::class) abstract class AppModule { @Binds abstract fun bindImageLoader(imageLoader: GlideImageLoader): ImageLoader ...
43. Scoping - Scoped bindings @Module @InstallIn(ApplicationComponent::class) abstract class AppModule { @Singleton @Binds abstract fun bindImageLoader(imageLoader: GlideImageLoader): ImageLoader ... ✅
44. Scoping - Scoped bindings @Module @InstallIn(ApplicationComponent::class) abstract class AppModule { @ActivityRetainedScoped @Binds abstract fun bindImageLoader(imageLoader: GlideImageLoader): ImageLoader ... ❌
45. Scoping - Scoped bindings
46. class HiltSampleViewModel @ViewModelInject constructor( private val hiltSampleRepository: HiltSampleRepository ) : ViewModel() { ... ActivityRetainedComponent Scoping - ViewModel bindings
47. Scoping - Predefined qualifiers @ActivityContext - Activity Context binding @ApplicationContext - Application Context binding
48. Scoping - Predefined qualifiers class HiltSampleRepositoryImpl @Inject constructor( @ActivityContext private val context: Context, private val hiltSampleService: HiltSampleService ) : HiltSampleRepository {
49. Scoping - Recommendation “only scope the binding if it’s required for the correctness of the code”
50. Dependency Injection - Hilt Usage - Multi-module apps
51. Multi-module apps - Gradle modules Regular gradle modules? ✅
52. Multi-module apps - Feature modules Feature Modules?
53. Multi-module apps - Feature modules “Hilt cannot process annotations in feature modules. You must use Dagger to perform dependency injection in your feature modules” Hilt + Dagger
54. Multi-module apps - Feature modules 1. Install an Entry Point in the Application Component from the app module
55. Multi-module apps - Feature modules 1. Install an Entry Point in the Application Component from the app module @EntryPoint @InstallIn(ApplicationComponent::class) interface ImageFeatureModule { fun imageLoader(): ImageLoader }
56. Multi-module apps - Feature modules 2. In the feature module, create a regular dagger component
57. Multi-module apps - Feature modules 2. In the feature module, create a regular dagger component @Component(dependencies = [ImageFeatureModule::class]) interface ImageFeatureComponent { fun inject(activity: ImageFeatureModuleActivity) @Component.Builder interface Builder { fun dependencies(imageFeatureModule: ImageFeatureModule): Builder fun build(): ImageFeatureComponent } }
58. Multi-module apps - Feature modules 3. Inject the dependency in the feature module
59. Multi-module apps - Feature modules 3. Inject the dependency in the feature module class ImageFeatureModuleActivity : AppCompatActivity() { @Inject lateinit var imageLoader: ImageLoader @AndroidEntryPoint
60. Multi-module apps - Feature modules 3. Inject the dependency in the feature module ... override fun onCreate(savedInstanceState: Bundle?) { DaggerImageFeatureComponent.builder() .dependencies( EntryPointAccessors.fromApplication( applicationContext, ImageFeatureModule::class.java ) ) .build() .inject(this)
61. Multi-module apps - Feature modules 3. Inject the dependency in the feature module ... override fun onCreate(savedInstanceState: Bundle?) { DaggerImageFeatureComponent.builder() .dependencies( EntryPointAccessors.fromApplication( applicationContext, ImageFeatureModule::class.java ) ) .build() .inject(this)
62. Dependency Injection - Migration Dagger Android -> Hilt
63. Migration - build.gradle
64. Migration - app/build.gradle
65. Migration - app/build.gradle
66. Migration - Application
67. Migration - Hilt_HiltSampleApplication.java (generated)
68. Migration - ViewModel
69. Migration - HiltSampleViewModel_AssistedFactory.java (generated)
70. Migration - HiltSampleViewModel_HiltModule.java (generated)
71. Migration - MainActivity
72. Migration - Hilt_MainActivity.java (generated)
73. Migration - Hilt_MainActivity.java (generated)
74. Migration - Modules
75. Migration - ViewModelFactory, ViewModelKey
76. Migration - HiltSampleApplication_HiltComponents.java (generated)
77. Resources • Dependency injection with Hilt • Dagger Hilt • Using Hilt in your Android app Codelab • Migrating your Dagger app to Hilt Codelab • Scoping in Android and Hilt. Scoping an object A to another object B… | by Manuel Vivo | Android Developers • Hilt in multi-module apps • https://github.com/moyheen/HiltSampleApplication • Image by Gerd Altmann from Pixabay
78. Thank You! Moyinoluwa Adeyemi @moyheen