Dagger + Anvil: Learning to Love Dependency Injection

This is a joint talk with Ralf Wondratschek from Square and Gabriel Peal from Tonal.

Anvil is a Kotlin compiler plugin that makes dependency injection with Dagger 2 easier. Anvil reduces boilerplate code, improves code modularization, reduces build times, and enables custom code generators to further simplify patterns specific to your codebase.

In this talk we will explain why Square created Anvil, how Tonal successfully adopted it, how the plugin works under the hood, what code is being generated and how you can get the most out of the framework.

Transcript

1. Dagger + Anvil
   Learning to Love Dependency Injection
   Ralf Wondratschek
   @vRallev
   Gabriel Peal
   @gpeal8
   

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2. Dagger 2 Refresher - Basic
   @Singleton
   @Component
   interface AppComponent
   class MainApplication : Application() {
   lateinit var component : AppComponent
   override fun onCreate () {
   super.onCreate()
   component = DaggerAppComponent.create()
   }
   }
   :app
   @Singleton
   class WeatherRepository @Inject constructor() {
   suspend fun getForecast(): List = TODO()
   }
   :feature.weather
   

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3. Dagger 2 Refresher - Interface + Impl
   @Singleton
   @Component(modules = [WeatherModule::class])
   interface AppComponent
   interface WeatherRepository {
   suspend fun getForecast(): List
   }
   :lib.weather
   @Singleton
   class WeatherRepositoryImpl @Inject constructor () : WeatherRepository {
   override suspend fun getForecast (): List = TODO()
   }
   @Module
   abstract class WeatherModule {
   @Binds
   abstract fun bindsWeatherRepository (r: WeatherRepositoryImpl ): WeatherRepository
   }
   :app
   :feature.weather
   

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4. Dagger 2 Refresher - Binding Interface
   @Singleton
   @Component
   interface AppComponent : WeatherBindings
   interface WeatherBindings {
   fun inject(fragment: WeatherFragment)
   fun weatherRepository(): WeatherRepository
   }
   :app
   :feature.weather
   

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5. Dagger 2 Refresher - Multibindings
   @Singleton
   @Component
   interface AppComponent
   :app
   interface WeatherDataSource {
   suspend fun getForecast
   (): List
   }
   class WeatherChannelDataSource @Inject constructor
   () : WeatherDataSource {
   override suspend fun getForecast
   (): List = TODO()
   }
   class WeatherUndergroundDataSource @Inject constructor
   (): WeatherDataSource {
   override suspend fun getForecast
   (): List = TODO()
   }
   @Singleton
   class WeatherRepository @Inject constructor
   (
   private val userPrefs: UserPrefs,
   private val dataSources
   : Map,
   ) {
   suspend fun getForecast
   (): List = TODO()
   }
   @Module
   abstract class WeatherModule {
   @Binds
   @IntoMap
   @StringKey ("WeatherChannel" )
   abstract fun bindsWeatherChannel (s: WeatherChannelDataSource ): WeatherDataSource
   @Binds
   @IntoMap
   @StringKey ("WeatherUnderground" )
   abstract fun bindsWeatherUnderground (s: WeatherUndergroundDataSource ): WeatherDataSource
   }
   :feature.weather
   (modules = [WeatherModule::class])
   

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6. Dagger 2
   ● Why it’s good
   ○ Build time guarantee
   ○ Fast at runtime (no reflection)
   ○ Huge community (Stack Overflow/Blog posts galore)
   ○ You can get it to do just about anything if you need it
   

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7. Dagger 2
   ● Why it’s not so good
   ○ Boilerplate
   ○ Complicated to learn (names aren’t great)
   ○ Build time (kapt)
   

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8. Why Anvil?
   ● Opinionated module structure
   ● Hundreds of demo applications
   → Boilerplate code became a problem
   

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9. Why Anvil?
   :app.1
   @Component(
   WeatherModule, LocationModule
   )
   AppComponent
   :app.2
   @Component(
   LocationModule, UserModule
   )
   AppComponent
   :app.3
   @Component(
   LocationModule, UserModule
   )
   AppComponent
   :feature.1
   WeatherModule
   :feature.2
   LocationModule
   :feature.3
   UserModule
   

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10. Why Anvil?
    Try to build :demo app
    Add missing dependencies
    in build.gradle file
    Sync :demo module in
    Android Studio
    Add Dagger modules to
    Dagger components
    

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11. Why Anvil?
    Try to build :demo app
    Add missing dependencies
    in build.gradle file
    Sync :demo module in
    Android Studio
    Add Dagger modules to
    Dagger components
    

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12. Why Anvil?
    @Singleton
    @Component(modules = [WeatherModule::class])
    interface AppComponent
    

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13. Why Anvil?
    @Singleton
    @Component(modules = [WeatherModule::class])
    interface AppComponent
    

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14. Why Anvil?
    ● A Dagger module must know to which component it belongs
    ● A Dagger component must know which modules it needs to
    include
    → The scope is the shared connection
    

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15. Why Anvil?
    @Component(modules = [WeatherModule::class])
    interface AppComponent
    @Module
    object WeatherModule
    

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16. Why Anvil?
    @MergeComponent(AppScope::class)
    interface AppComponent
    @Module
    @ContributesTo(AppScope::class)
    object WeatherModule
    

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17. Why Anvil?
    @MergeComponent(AppScope::class)
    interface AppComponent
    @Module
    @ContributesTo(AppScope::class)
    object WeatherModule
    

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18. Why Anvil?
    :app.1
    @Component(
    WeatherModule, LocationModule
    )
    AppComponent
    :app.2
    @Component(
    LocationModule, UserModule
    )
    AppComponent
    :app.3
    @Component(
    LocationModule, UserModule
    )
    AppComponent
    :feature.1
    WeatherModule
    :feature.2
    LocationModule
    :feature.3
    UserModule
    

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19. Why Anvil?
    :app.1
    @MergeComponent(AppScope)
    AppComponent
    :app.2
    @MergeComponent(AppScope)
    AppComponent
    :app.3
    @MergeComponent(AppScope)
    AppComponent
    :feature.1
    @ContributesTo(AppScope)
    WeatherModule
    :feature.2
    @ContributesTo(AppScope)
    LocationModule
    :feature.3
    @ContributesTo(AppScope)
    UserModule
    

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20. Why Anvil?
    :app.1
    @MergeComponent(AppScope)
    AppComponent
    :app.2
    @MergeComponent(AppScope)
    AppComponent
    :app.3
    @MergeComponent(AppScope)
    AppComponent
    :feature.1
    @ContributesTo(AppScope)
    WeatherModule
    :feature.2
    @ContributesTo(AppScope)
    LocationModule
    :feature.3
    @ContributesTo(AppScope)
    UserModule
    :core
    object AppScope
    

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21. Why Anvil?
    ● Allows you to construct the dependency graph in a loose
    way
    ● Aligns the build graph with the dependency graph
    ● Moves decision which scope to use to the declaration side
    ● Allows you to add new Dagger modules easily to all apps
    ● Creating new applications is faster
    

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22. Dagger 2 - Basic
    @Singleton
    @Component
    interface AppComponent
    class MainApplication : Application() {
    lateinit var component : AppComponent
    override fun onCreate () {
    super.onCreate()
    component = DaggerAppComponent.create()
    }
    }
    :app
    @Singleton
    class WeatherRepository @Inject constructor() {
    suspend fun getForecast(): List = TODO()
    }
    :feature.weather
    

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23. Anvil - Basic
    @Singleton
    @MergeComponent(AppScope::class)
    interface AppComponent
    class MainApplication : Application() {
    lateinit var component : AppComponent
    override fun onCreate () {
    super.onCreate()
    component = DaggerAppComponent.create()
    }
    }
    @Singleton
    class WeatherRepository @Inject constructor() {
    suspend fun getForecast(): List = TODO()
    }
    interface AppScope
    :app
    :feature.weather
    :lib.scopes
    

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24. Anvil - Basic
    @Singleton
    @MergeComponent(AppScope::class)
    interface AppComponent
    Two different names to memorize
    

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25. Anvil - Basic
    @SingleIn(AppScope::class)
    @MergeComponent(AppScope::class)
    interface AppComponent
    Two different names to memorize
    

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26. Anvil - Basic
    @Singleton
    @MergeComponent(AppScope::class)
    interface AppComponent
    class MainApplication : Application() {
    lateinit var component: AppComponent
    override fun onCreate() {
    super.onCreate()
    component = DaggerAppComponent.create()
    }
    }
    @Singleton
    class WeatherRepository @Inject constructor() {
    suspend fun getForecast(): List = TODO()
    }
    interface AppScope
    :app
    :feature.weather
    :lib.scopes
    @Scope
    @Retention(AnnotationRetention.RUNTIME)
    annotation class SingleIn(val clazz: KClass<*>)
    

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27. Anvil - Basic
    @SingleIn(AppScope::class)
    @MergeComponent(AppScope::class)
    interface AppComponent
    class MainApplication : Application() {
    lateinit var component: AppComponent
    override fun onCreate() {
    super.onCreate()
    component = DaggerAppComponent.create()
    }
    }
    @SingleIn(AppScope::class)
    class WeatherRepository @Inject constructor() {
    suspend fun getForecast(): List = TODO()
    }
    interface AppScope
    :app
    :feature.weather
    :lib.scopes
    @Scope
    @Retention(AnnotationRetention.RUNTIME)
    annotation class SingleIn(val clazz: KClass<*>)
    

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28. Dagger 2 - Interface + Impl
    @Singleton
    @Component(modules = [WeatherModule::class])
    interface AppComponent
    interface WeatherRepository {
    suspend fun getForecast(): List
    }
    :lib.weather
    @Singleton
    class WeatherRepositoryImpl @Inject constructor () : WeatherRepository {
    override suspend fun getForecast (): List = TODO()
    }
    @Module
    abstract class WeatherModule {
    @Binds
    abstract fun bindsWeatherRepository (r: WeatherRepositoryImpl ): WeatherRepository
    }
    :app
    :feature.weather
    BOILERPLATE 🔥
    

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29. Anvil - Interface + Impl
    @SingleIn(AppScope::class)
    @ContributesBinding(AppScope::class)
    class WeatherRepositoryImpl @Inject constructor() : WeatherRepository
    {
    override suspend fun getForecast(): List = TODO()
    }
    :lib.weather
    :feature.weather
    interface WeatherRepository {
    suspend fun getForecast(): List
    }
    @Singleton
    @MergeComponent(AppScope::class)
    interface AppComponent
    :app
    

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30. Dagger 2 - Binding Interface
    @Singleton
    @Component
    interface AppComponent : WeatherBindings
    interface WeatherBindings {
    fun inject(fragment: WeatherFragment)
    fun weatherRepository(): WeatherRepository
    }
    :app
    :feature.weather
    BOILERPLATE 🔥
    

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31. Anvil - Binding Interface
    @ContributesTo(AppScope::class)
    interface WeatherBindings {
    fun inject(fragment: WeatherFragment)
    fun weatherRepository(): WeatherRepository
    }
    :feature.weather
    @Singleton
    @MergeComponent(AppScope::class)
    interface AppComponent
    :app
    

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32. Dagger 2 - Multibindings
    @Singleton
    @Component(modules = [WeatherModule::class])
    interface AppComponent
    interface WeatherDataSource {
    suspend fun getForecast
    (): List
    }
    class WeatherChannelDataSource @Inject constructor
    () : WeatherDataSource {
    override suspend fun getForecast
    (): List = TODO()
    }
    class WeatherUndergroundDataSource @Inject constructor
    (): WeatherDataSource {
    override suspend fun getForecast
    (): List = TODO()
    }
    @Singleton
    class WeatherRepository @Inject constructor
    (
    private val userPrefs: UserPrefs,
    private val dataSources
    : Map,
    ) {
    suspend fun getForecast
    (): List = TODO()
    }
    @Module
    abstract class WeatherModule {
    @Binds
    @IntoMap
    @StringKey ("WeatherChannel" )
    abstract fun bindsWeatherChannel (s: WeatherChannelDataSource ): WeatherDataSource
    @Binds
    @IntoMap
    @StringKey ("WeatherUnderground" )
    abstract fun bindsWeatherUnderground (s: WeatherUndergroundDataSource ): WeatherDataSource
    }
    :app
    :feature.weather
    BOILERPLATE 🔥
    BOILERPLATE 🔥
    

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33. Anvil - Multibindings
    @Singleton
    @MergeComponent(AppScope::class)
    interface AppComponent
    :app
    :feature.weather
    interface WeatherDataSource {
    suspend fun getForecast(): List
    }
    @StringKey("WeatherChannel")
    @ContributesMultibinding(AppScope::class)
    class WeatherChannelDataSource @Inject constructor() :
    WeatherDataSource {
    override suspend fun getForecast(): List =
    TODO()
    }
    @StringKey("WeatherUnderground")
    @ContributesMultibinding(AppScope::class)
    class WeatherUndergroundDataSource @Inject constructor():
    WeatherDataSource {
    override suspend fun getForecast(): List =
    TODO()
    }
    @Singleton
    class WeatherRepository @Inject constructor(
    private val userPrefs: UserPrefs,
    private val dataSources: Map,
    ) {
    suspend fun getForecast(): List =
    TODO()
    }
    

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34. /* :app /src/main */
    @SingleIn(AppScope::class)
    @MergeComponent(AppScope::class)
    interface AppComponent
    open class MainApplication : Application() {
    lateinit var daggerComponent: Any
    override fun onCreate() {
    super.onCreate()
    daggerComponent = DaggerAppComponent.create()
    }
    }
    Anvil - Replace dependencies in tests
    

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35. /* :app /src/androidTest */
    @SingleIn(AppScope::class)
    @MergeComponent(AppScope::class)
    interface TestAppComponent
    class TestApplication : MainApplication() {
    override lateinit var daggerComponent: Any
    override fun onCreate() {
    super.onCreate()
    daggerComponent = DaggerTestAppComponent.create()
    }
    }
    Anvil - Replace dependencies in tests
    

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36. /* :lib.weatherdata /src/main */
    interface WeatherRepository {
    suspend fun getForecast(): List
    }
    /* :features.weatherdata /src/main */
    @SingleIn(WeatherScope::class)
    @ContributesBinding(WeatherScope::class)
    class WeatherRepositoryImpl @Inject constructor() : WeatherRepository
    Anvil - Replace dependencies in tests
    

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37. /* :lib.weatherdata /src/main */
    interface WeatherRepository {
    suspend fun getForecast(): List
    }
    /* :app /src/androidTest */
    @ContributesBinding(
    scope = WeatherScope::class
    )
    object FakeWeatherRepository : WeatherRepository {
    override suspend fun getForecast(): List = listOf(1, 2, 3, 4, 5)
    }
    Anvil - Replace dependencies in tests
    

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38. /* :lib.weatherdata /src/main */
    interface WeatherRepository {
    suspend fun getForecast(): List
    }
    /* :app /src/androidTest */
    @ContributesBinding(
    scope = WeatherScope::class,
    replaces = [WeatherRepositoryImpl::class]
    )
    object FakeWeatherRepository : WeatherRepository {
    override suspend fun getForecast(): List = listOf(1, 2, 3, 4, 5)
    }
    Anvil - Replace dependencies in tests
    

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39. /* :lib.weatherdata /src/main */
    interface WeatherRepository {
    suspend fun getForecast(): List
    }
    /* :app /src/androidTest */
    @ContributesBinding(
    scope = WeatherScope::class,
    replaces = [WeatherRepositoryImpl::class]
    )
    object FakeWeatherRepository : WeatherRepository {
    override suspend fun getForecast(): List = listOf(1, 2, 3, 4, 5)
    }
    Anvil - Replace dependencies in tests
    

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40. What about Hilt?
    ● Multi-login
    ● Guarantee no user information leaks
    across accounts
    ● Null safe access to account
    

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41. What about Hilt?
    class WorkoutFragment : Fragment( R.layout.workout_fragment), DaggerComponentOwner {
    // github/gpeal/Anvil-Sample
    override val daggerComponent : WeatherComponent by fragmentComponent { scope, app ->
    app.bindings().workoutComponentBuilder().create(scope)
    }
    }
    

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42. What about Hilt?
    

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43. What about Hilt?
    

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44. Anvil - Build Time
    

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45. Anvil - Dagger Factory Generation
    plugins {
    id 'org.jetbrains.kotlin.kapt'
    id 'com.squareup.anvil'
    }
    dependencies {
    api "com.google.dagger:dagger:$daggerVersion"
    kapt "com.google.dagger:dagger-compiler:$daggerVersion"
    }
    

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46. Anvil - Dagger Factory Generation
    plugins {
    id 'com.squareup.anvil'
    }
    anvil {
    generateDaggerFactories = true
    }
    dependencies {
    api "com.google.dagger:dagger:$daggerVersion"
    }
    

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47. Build time for single modules improved by up to 65%
    Anvil - Dagger Factory Generation
    

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48. Build time for our full project improved by 16% on average
    Anvil - Build time
    

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49. Build time for Slack improved by 25%
    Anvil - Build time
    

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50. TL;DR
    ● If you use Dagger already, then Anvil will make your build
    times significantly faster and provide more features on top
    ○ (For Dagger + Hilt the diff is even bigger)
    Anvil - Build time
    

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51. Extend Anvil - Custom Code Generator
    interface WeatherApi {
    @GET("…")
    suspend fun getForecast(): Forecast
    }
    @Module
    @ContributesTo(AppScope::class)
    object WeatherApiModule {
    @Provides
    @Reusable
    fun providesWeatherApi(retrofit: Retrofit): WeatherApi {
    return retrofit.create()
    }
    }
    @ContributesApi(AppScope::class)
    Eliminated
    // github/gpeal/Avil-Sample
    

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52. @Module
    @ContributesTo(AppScope::class)
    public abstract class WeatherViewModelModule {
    @Binds
    @IntoMap
    @ViewModelKey(WeatherViewModel::class)
    public abstract fun bindWeatherViewModelFactory(
    factory: WeatherViewModel.Factory,
    ): TonalViewModelFactory<*, *>
    }
    Extend Anvil - Custom Code Generator
    @ContributesViewModel(UserScope::class)
    class WeatherViewModel @AssistedInject constructor(
    @Assisted initialState: WeatherState,
    weatherRepository: WeatherRepository,
    ) : MavericksViewModel(initialState) {
    …
    }
    Eliminated
    

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53. Extend Anvil - Custom Code Generator
    @ContributesFeatureFlag
    enum class MyFeatureFlag(
    override val flag: String,
    ) : BaseFeatureFlag {
    MyFlag("my-flag"),
    MyFlag2("my-flag-2"),
    }
    @Module
    @ContributesTo(AppScope::class)
    public abstract class MyFeatureFlagModule {
    @Provides
    @ElementsIntoSet
    fun providesMyFeatureFlags(): Set = MyFeatureFlag.values().toSet()
    }
    Eliminated
    

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54. Extend Anvil - Custom Code Generator
    

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55. Thank you!
    Ralf Wondratschek
    @vRallev
    Gabriel Peal
    @gpeal8
    github.com/gpeal/Anvil-Sample
    

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56. Resources
    ● https://github.com/square/anvil
    ● https://github.com/gpeal/Anvil-Sample
    ● https://gpeal.medium.com/dagger-anvil-learning-to-love-d
    ependency-injection-on-android-8fad3d5530c9
    

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