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Effective DI with Multi-Modular Architecture

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Adit Lal GoPay $6.3B @aditlal We have 18+ products from food tech to fin-tech to hyper local delivery and massage services Ride Sharing 16.5m KM

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app core feature 2 feature 1 Monolith Expensive Object

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What could possibly go wrong?

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Solve DI with Multi-Modular codebase

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Modularise?

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app core Feature B Feature A Feature modules Expensive Object

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• Organise and decouple independent pieces of functionality • Improve project build times • Define clear ownership boundaries between different teams Thoughts on modularisation

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Feature module : • Owned by single team ? Set of team members • Encapsulates single feature • Single entry point • Smaller is better • Cannot depend on other feature modules Thoughts on modularisation

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App module : • No feature-specific code • No infrastructure-specific code. • Creates the dagger component Thoughts on modularisation

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Ownership? core auth common Feature n-1 Feature n+2 Feature n-2 Feature z Feature n Feature n+1 app … … … … …

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Ownership? core auth common Feature n-1 Feature n+2 Feature n-2 Feature z Feature n Feature n+1 app … … … … …

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Inversion of control Dependency Inversion Dependency Injection IoC Principle

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• Declare Components that can be reused. • High level modules should not depend on low level modules • Build abstractions so any implementation can be easily changed with new one. • Dependencies can be injected into components. IoC Principle

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Should I do Modularise to use Dagger?

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Don’t do it for Dagger , do it for yourself

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:feature1 F1SubComponent F1Module :feature2 F2SubComponent F2Module :core CoreComponent CoreModule Expensive Object :app MainComponent MainModule

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:app MainComponent MainModule :feature1 F1Component F1Module :feature2 F2Component F2Module :core CoreComponent CoreModule Expensive Object

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• We should prefer to be explicit with the module dependencies
 • We don’t want CoreComponent to know about FeatureComponent
 • It can’t check if the graph is correct. SubComponent goes away! It needs the parent = slower compilation


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Core @Module class CoreModule { @Provides @Singleton fun provideExpObj(): ExpensiveObject = ExpensiveObject() }

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@Component(modules = [CoreModule::class]) @Singleton interface CoreComponent { @Component.Builder interface Builder { fun build(): CoreComponent } fun provideExpensiveObject(): ExpensiveObject } Core

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class OurMainApplication : Application() { private val coreComponent: CoreComponent by lazy { DaggerCoreComponent .builder() .build() } companion object { @JvmStatic fun coreComponent(context: Context) = (context.applicationContext as OurMainApplication).coreComponent } }

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class OurMainApplication : Application() { private val coreComponent: CoreComponent by lazy { DaggerCoreComponent .builder() .build() } companion object { @JvmStatic fun coreComponent(context: Context) = (context.applicationContext as OurMainApplication).coreComponent } }

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class OurMainApplication : Application() { private val coreComponent: CoreComponent by lazy { DaggerCoreComponent .builder() .build() } companion object { @JvmStatic fun coreComponent(context: Context) = (context.applicationContext as OurMainApplication).coreComponent } }

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fun Activity.coreComponent() = OurMainApplication.coreComponent(this) Extension function

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@Module class Feature1Module { @Provides fun provideString() = "test" } Feature 1

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@Component(modules = [Feature1Module::class], dependencies = [CoreComponent::class]) interface Feature1Component { @Component.Builder interface Builder { fun coreComponent(coreComponent: CoreComponent): Builder } fun inject(activity: OtherActivity) } Feature 1

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DaggerFeature1Component .builder() .coreComponent(this.coreComponent) .build() .inject(this) Feature 1

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@Module class Feature2Module { @Provides fun provideInt() = 1 } Feature 2

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@Component(modules = [Feature2Module::class], dependencies = [CoreComponent::class]) interface Feature2Component { @Component.Builder interface Builder { fun coreComponent(coreComponent: CoreComponent): Builder } fun inject(activity: MainActivity) } Feature 2

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When dealing with component dependencies we must follow 2 simple rules: • An un-scoped component cannot depend on scoped components. • A scoped component cannot depend on a component with the same scope.

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@Scope @Retention annotation class FeatureScope

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@Component(modules = [Feature1Module::class], dependencies = [CoreComponent::class]) @FeatureScope interface Feature1Component { @Component.Builder interface Builder { fun coreComponent(coreComponent: CoreComponent): Builder } fun inject(activity: OtherActivity) }

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@Component(modules = [Feature2Module::class], dependencies = [CoreComponent::class]) @FeatureScope interface Feature2Component { @Component.Builder interface Builder { fun coreComponent(coreComponent: CoreComponent): Builder } fun inject(activity: MainActivity) }

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Component.dependencies • We can choose what we expose from each component • more verbosity • we can get dependencies from multiple components faster compilation

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Let’s get to it

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interface CoreComponentProvider { fun provideCoreComponent(): CoreComponent }

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object CoreInjectHelper { fun provideCoreComponent(applicationContext: Context): CoreComponent{ return if (applicationContext is CoreComponentProvider) { (applicationContext as CoreComponentProvider).provideCoreComponent() } else { throw IllegalStateException( "The context passed does not implement CoreComponentProvider" ) } } }

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object CoreInjectHelper { fun provideCoreComponent(applicationContext: Context): CoreComponent{ return if (applicationContext is CoreComponentProvider) { (applicationContext as CoreComponentProvider).provideCoreComponent() } else { throw IllegalStateException( "The context passed does not implement CoreComponentProvider" ) } } }

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object CoreInjectHelper { fun provideCoreComponent(applicationContext: Context): CoreComponent{ return if (applicationContext is CoreComponentProvider) { (applicationContext as CoreComponentProvider).provideCoreComponent() } else { throw IllegalStateException( "The context passed does not implement CoreComponentProvider" ) } } }

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class OurMainApplication : Application(), CoreComponentProvider { private lateinit var coreComponent: CoreComponent override fun provideCoreComponent(): CoreComponent { if (!this::coreComponent.isInitialized) { coreComponent = DaggerCoreComponent .builder() .build() } return coreComponent } }

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class OurMainApplication : Application(), CoreComponentProvider { private lateinit var coreComponent: CoreComponent override fun provideCoreComponent(): CoreComponent { if (!this::coreComponent.isInitialized) { coreComponent = DaggerCoreComponent .builder() .build() } return coreComponent } }

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class OurMainApplication : Application(), CoreComponentProvider { private lateinit var coreComponent: CoreComponent override fun provideCoreComponent(): CoreComponent { if (!this::coreComponent.isInitialized) { coreComponent = DaggerCoreComponent .builder() .build() } return coreComponent } }

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class MainActivity : AppCompatActivity() { @Inject lateinit var expensiveObject: ExpensiveObject override fun onCreate(savedInstanceState: Bundle?) { ... DaggerFeature2Component .builder() .coreComponent(this.coreComponent()) .build() .inject(this) } }

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class MainActivity : AppCompatActivity() { @Inject lateinit var expensiveObject: ExpensiveObject override fun onCreate(savedInstanceState: Bundle?) { ... DaggerFeature2Component .builder() .coreComponent(this.coreComponent()) .build() .inject(this) } }

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Dagger.Android

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@Scope annotation class ActivityScope

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@Module(includes = [ AndroidSupportInjectionModule::class ]) abstract class AppModule { @ActivityScope @ContributesAndroidInjector() abstract fun contributesMainActivityInjector(): MainActivity @ActivityScope @ContributesAndroidInjector() abstract fun contributesOtherActivityInjector(): OtherActivity }

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@Module(includes = [ AndroidSupportInjectionModule::class ]) abstract class AppModule { @ActivityScope @ContributesAndroidInjector() abstract fun contributesMainActivityInjector(): MainActivity @ActivityScope @ContributesAndroidInjector() abstract fun contributesOtherActivityInjector(): OtherActivity }

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class OurMainApplication : Application(), CoreComponentProvider, HasActivityInjector { @Inject lateinit var dispatchingActivityInjector: DispatchingAndroidInjector private lateinit var coreComponent: CoreComponent override fun onCreate() { super.onCreate() DaggerAppComponent.create().inject(this) } override fun activityInjector(): AndroidInjector = dispatchingActivityInjector }

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class OurMainApplication : Application(), CoreComponentProvider, HasActivityInjector { @Inject lateinit var dispatchingActivityInjector: DispatchingAndroidInjector private lateinit var coreComponent: CoreComponent override fun onCreate() { super.onCreate() DaggerAppComponent.create().inject(this) } override fun activityInjector(): AndroidInjector = dispatchingActivityInjector }

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class OurMainApplication : Application(), CoreComponentProvider, HasActivityInjector { @Inject lateinit var dispatchingActivityInjector: DispatchingAndroidInjector private lateinit var coreComponent: CoreComponent override fun onCreate() { super.onCreate() DaggerAppComponent.create().inject(this) } override fun activityInjector(): AndroidInjector = dispatchingActivityInjector }

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class OurMainApplication : Application(), CoreComponentProvider, HasActivityInjector { @Inject lateinit var dispatchingActivityInjector: DispatchingAndroidInjector private lateinit var coreComponent: CoreComponent override fun onCreate() { super.onCreate() DaggerAppComponent.create().inject(this) } override fun activityInjector(): AndroidInjector = dispatchingActivityInjector }

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class MainActivity : AppCompatActivity() { @Inject lateinit var expensiveObject: ExpensiveObject override fun onCreate(savedInstanceState: Bundle?) { AndroidInjection.inject(this) ... } }

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class MainActivity : AppCompatActivity() { @Inject lateinit var expensiveObject: ExpensiveObject override fun onCreate(savedInstanceState: Bundle?) { AndroidInjection.inject(this) ... } }

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AndroidInjection.inject(this) Activity Fragment Service Content Provider Broadcast Receiver this

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Tip @Inject lateinit var expensiveObject: Lazy expensiveObject.get()

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• Always go for static provide methods. • Nobody cares about name of your Scope • Expose the application context through a component builder instead of a module with constructor argument. Or even better: use the new factory! Tip

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@Module class Feature1Module { @Provides fun provideString() = "test" } Tip

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@Module abstract class Feature1Module { @Binds abstract fun provideString() } Tip

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Tip Module Module Factory Component @Provides Create a inject object Component @Binds Create a inject object

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Tip @Binds @IntoMap @ViewModelKey(X1::class) abstract bindUserViewModel(x1 : ObjX) : ObjX

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• Provide dependencies through class constructors • Avoid unnecessary scoping - Use scope annotations sparingly and judiciously Tl;Dr

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• Use reusable components for expensive and immutable dependencies • Use @Binds instead of a @Provides method when simply delegating one type to another. • Write tests , switch dependencies on tests with a test component instead of overriding modules. Tl;Dr

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• Using Dagger in multi-module by Marcos Holgado • Dependency injection in a multi module project - Plaid - Ben Weiss • Modularising Android Application by Marvin Ramin Resources

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https://superapp.is https://www.gojek.io

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Adit Lal @aditlal adit.dev Thats all folks!