Understanding Advanced Dagger Concepts (Part 2)

Singleton and Lifecycle

Use scopes like @Singleton to ensure only one instance exists through app lifetime.

Dagger Evolution

Dagger was initially built by Square using reflection which is slower comparatively. Next is from, Google’s Dagger 2 generates code at compile time, making apps faster and safer.

Organizing Dagger in Your Project

Create a di folder with:

• modules/ for classes providing dependencies (@Module with @Provides)

• components/ for interfaces connecting providers and consumers annotated with @Component

• Files with scopes and qualifier annotations

Sample Module

@Module
class EngineModule {

    @Provides
    fun provideMotor(): Motor = FastMotor()

    @Provides
    fun provideEngine(motor: Motor): Engine = Engine(motor)
}

Sample Component

kotlin@Singleton
@Component(modules = [EngineModule::class])
interface AppComponent {
    fun inject(car: Car)
}

Injection Example

kotlinclass Car @Inject constructor(val engine: Engine) {
    fun drive() {
        engine.ignite()
        println("Car is driving")
    }
}

Injection can also be done by fields or methods

Big Bucket vs Small Bucket

Big bucket (Application scope) vs small bucket (Activity/Fragment scope) manage dependency lifetimes differently.

Gradle Dependencies Reminder

implementation "com.google.dagger:dagger:2.xx"
kapt "com.google.dagger:dagger-compiler:2.xx"

dagger-compiler generates code during compile-time via KotlinPoet or JavaPoet, improving performance.

Missed the previous parts of this Dagger series? Start here:

• Learning Dagger Dependency Injection Quickly and Easily

• Understanding Core Dagger Concepts (Part 1)

---