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.

Transcript

1. Hilt the DI ground
   running
   Moyinoluwa Adeyemi
   @moyheen
   

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2. What is Dependency Injection?
   

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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
   

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4. Dependency Injection
   

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5. Dependency Injection
   

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6. No Dependency Injection
   class RoboGardener {
   fun waterPlant() {
   val waterSource = WaterSource()
   waterSource.dispenseWater()
   }
   }
   

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7. Dependency Injection - Constructor
   class RoboGardener(private val waterSource: WaterSource) {
   fun waterPlant() {
   waterSource.dispenseWater()
   }
   }
   

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8. Dependency Injection - Constructor
   class RoboGardener(private val waterSource: WaterSource) {
   fun waterPlant() {
   waterSource.dispenseWater()
   }
   }
   fun main() {
   val roboGardener = RoboGardener(CupOfWater())
   roboGardener.waterPlant()
   }
   

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9. Dependency Injection - Setter
   class RoboGardener {
   lateinit var waterSource: WaterSource
   fun waterPlant() {
   waterSource.dispenseWater()
   }
   }
   

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10. Dependency Injection - Setter
    class RoboGardener {
    lateinit var waterSource: WaterSource
    fun waterPlant() {
    waterSource.dispenseWater()
    }
    }
    fun main() {
    val roboGardener = RoboGardener()
    roboGardener.waterSource = WateringCan()
    roboGardener.waterPlant()
    }
    

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11. Dependency Injection - Interface
    interface WaterSourceManager {
    fun provideWaterSource(waterSource: WaterSource)
    }
    

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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
    }
    ...
    

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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()
    }
    

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14. RoboGardener WaterSource
    Dependency Injection - Graph
    

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15. Service Locators
    

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16. Service Locators
    class RoboGardener {
    fun waterPlant() {
    val waterSource = CupOfWater()
    waterSource.dispenseWater()
    }
    }
    

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17. class RoboGardener {
    fun waterPlant() {
    val waterSource = ServiceLocator.getInstance.findWaterSource()
    waterSource.dispenseWater()
    }
    }
    Service Locators
    

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18. No
    increase
    in app
    size
    Manual Dependency Injection
    
    

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19. Manual Dependency Injection
    No
    increase
    in app
    size
    
    Low
    Learning
    Curve
    
    

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20. High
    maintenance
    costs
    Manual Dependency Injection
    Low
    Learning
    Curve
    No
    increase
    in app
    size
    
    
    ♀
    

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21. Dependency Injection - Dagger
    Dagger
    Code generation
    Steep learning curve
    For Java or Kotlin developers
    Useful for large projects
    

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22. Dependency Injection - Hilt
    What is different?
    

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23. Dependency Injection - Hilt
    Low
    Learning
    Curve
    
    

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24. Dependency Injection - Hilt
    Low
    Learning
    Curve
    
    Free
    Lifecycle
    Management
    ♻
    

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25. Dependency Injection - Hilt
    Low
    Learning
    Curve
    
    Free
    Lifecycle
    Management
    ♻
    Co-exist
    with
    Dagger
    ♂
    

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26. Dependency Injection - Hilt
    Usage - Annotations
    

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27. @HiltAndroidApp
    class HiltSampleApplication : Application()
    @HiltAndroidApp
    

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28. @AndroidEntryPoint
    class MainActivity : AppCompatActivity() {
    @Inject lateinit var imageLoader: ImageLoader
    private val viewModel: HiltSampleViewModel by viewModels()
    ...
    @AndroidEntryPoint
    

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29. Activity
    imageLoader
    viewModel
    @AndroidEntryPoint
    

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30. @Module
    @InstallIn(ApplicationComponent::class)
    abstract class AppModule
    @InstallIn
    

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31. @Module
    @InstallIn(ApplicationComponent::class)
    abstract class AppModule {
    @Binds
    abstract fun bindImageLoader(imageLoader: GlideImageLoader): ImageLoader
    ...
    }
    @InstallIn
    

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32. @Module
    @InstallIn(ApplicationComponent::class)
    object NetworkModule {
    @Provides
    fun providesMoshi(): Moshi = Moshi.Builder()
    .build()
    ...
    @InstallIn
    

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33. class HiltSampleViewModel @ViewModelInject constructor(
    private val hiltSampleRepository: HiltSampleRepository
    ) : ViewModel() {
    ...
    ViewModels - @ViewModelInject
    

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34. ViewModel
    repository
    ViewModels - @ViewModelInject
    Activity
    imageLoader
    viewModel
    

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35. @AndroidEntryPoint
    @AndroidEntryPoint
    class MainActivity : AppCompatActivity() {
    @Inject lateinit var imageLoader: ImageLoader
    private val viewModel: HiltSampleViewModel by viewModels()
    ...
    

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36. @EntryPoint - Interface
    @EntryPoint
    @InstallIn(ApplicationComponent::class)
    interface ImageFeatureModule {
    fun imageLoader(): ImageLoader
    }
    

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37. @EntryPoint - Dependency retrieval
    val imageLoader = EntryPoints
    .get(applicationContext, ImageFeatureModule::class.java)
    .imageLoader()
    

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38. @EntryPoint - Interface retrieval
    EntryPointAccessors.fromApplication(
    applicationContext,
    ImageFeatureModule::class.java
    )
    

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39. Dependency Injection - Hilt
    Usage - Scoping
    

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40. https://developer.android.com/training/dependency-injection/hilt-android#component-scopes
    Scoping
    

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41. https://dagger.dev/hilt/component-hierarchy.svg
    Scoping - Hierarchy
    

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42. Scoping - Unscoped bindings
    @Module
    @InstallIn(ApplicationComponent::class)
    abstract class AppModule {
    @Binds
    abstract fun bindImageLoader(imageLoader: GlideImageLoader): ImageLoader
    ...
    

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43. Scoping - Scoped bindings
    @Module
    @InstallIn(ApplicationComponent::class)
    abstract class AppModule {
    @Singleton
    @Binds
    abstract fun bindImageLoader(imageLoader: GlideImageLoader): ImageLoader
    ...
    ✅
    

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44. Scoping - Scoped bindings
    @Module
    @InstallIn(ApplicationComponent::class)
    abstract class AppModule {
    @ActivityRetainedScoped
    @Binds
    abstract fun bindImageLoader(imageLoader: GlideImageLoader): ImageLoader
    ...
    ❌
    

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45. Scoping - Scoped bindings
    

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46. class HiltSampleViewModel @ViewModelInject constructor(
    private val hiltSampleRepository: HiltSampleRepository
    ) : ViewModel() {
    ...
    ActivityRetainedComponent
    Scoping - ViewModel bindings
    

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47. Scoping - Predefined qualifiers
    @ActivityContext - Activity Context binding
    @ApplicationContext - Application Context binding
    

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48. Scoping - Predefined qualifiers
    class HiltSampleRepositoryImpl @Inject constructor(
    @ActivityContext private val context: Context,
    private val hiltSampleService: HiltSampleService
    ) : HiltSampleRepository {
    

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49. Scoping - Recommendation
    “only scope the binding if it’s required for the correctness of the
    code”
    

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50. Dependency Injection - Hilt
    Usage - Multi-module apps
    

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51. Multi-module apps - Gradle modules
    Regular gradle modules? ✅
    

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52. Multi-module apps - Feature modules
    Feature Modules?
    

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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
    

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54. Multi-module apps - Feature modules
    1. Install an Entry Point in the Application Component from the app module
    

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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
    }
    

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56. Multi-module apps - Feature modules
    2. In the feature module, create a regular dagger component
    

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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
    }
    }
    

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58. Multi-module apps - Feature modules
    3. Inject the dependency in the feature module
    

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59. Multi-module apps - Feature modules
    3. Inject the dependency in the feature module
    class ImageFeatureModuleActivity : AppCompatActivity() {
    @Inject lateinit var imageLoader: ImageLoader
    @AndroidEntryPoint
    

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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)
    

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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)
    

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62. Dependency Injection - Migration
    Dagger Android -> Hilt
    

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63. Migration - build.gradle
    

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64. Migration - app/build.gradle
    

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65. Migration - app/build.gradle
    

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66. Migration - Application
    

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67. Migration - Hilt_HiltSampleApplication.java (generated)
    

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68. Migration - ViewModel
    

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69. Migration - HiltSampleViewModel_AssistedFactory.java (generated)
    

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70. Migration - HiltSampleViewModel_HiltModule.java (generated)
    

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71. Migration - MainActivity
    

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72. Migration - Hilt_MainActivity.java (generated)
    

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73. Migration - Hilt_MainActivity.java (generated)
    

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74. Migration - Modules
    

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75. Migration - ViewModelFactory, ViewModelKey
    

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76. Migration - HiltSampleApplication_HiltComponents.java (generated)
    

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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
    

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78. Thank You!
    Moyinoluwa Adeyemi
    @moyheen
    

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