Dagger 2

Introduction

Dagger is made by Google. Dagger allows you to

• Scope dependencies
• Bind single instance to life cycles
• Only need to build them once
• Generates the code at compile time

Example Without Dagger

fun buildCar: Car =  
    Car(SturdyFrame(),
    Wheels(),
    RocketEngine())

With Dagger

fun buildCar: Car = 
    DaggerAppComponent
    .builder()
    .build()
    .buildCar()

Modules

Modules in Dagger are responsible for providing object we want to inject. They contain the methods which return the objects. Modules are decorated with @module and the objects are decorated with @provides @Module fun CarModule {

   @Provides
   fun provideEngine() : Engine = Engine()

   @Provides
   fun provideFrame() : Frame = Frame()

   @Provides
   fun provideWheels() : Wheels = Wheels()

   @Provides
   fun provideCar(engine: Engine, wheels: Wheels, frame: Frame) : Car {
     return Car(frame, wheels, engine)
   }

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