Binding is missing in Dagger2?

Issue

I have made a simple app that tells the car is a two-wheeler or four-wheeler with the help of dagger2 but an error will occur if I run the app and the error is binding is missing for this I have also used @Named annotation but the error is coming again and again.

MainActivity.kt

class MainActivity : AppCompatActivity() {

    @Inject
    lateinit var car: Car
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        DaggerCarComp.builder().build().inject(this)

        car.tellCarTypes()

    }
}

Car.kt

class Car @Inject constructor(
    @Named("two") val tw: TW,
     val fw: FW
) {
    fun tellCarTypes() {
        tw.whichCar()
    }
}

CarComp.kt

@Component(modules = [CarModule::class])
interface CarComp {
    fun inject (mainActivity: MainActivity)
}

CarType.kt

interface CarType {
    fun whichCar()
}

class TW @Inject constructor() : CarType {
    override fun whichCar() {
        Log.d("Type", "whichCar: Two wheeler")
    }
}

class FW : CarType {
    override fun whichCar() {
        Log.d("Type", "whichCar: Four wheeler")
    }
}

CarModule.kt

@Module
class CarModule {
    @Provides
    @Named("two")
    fun tellCar(tw: TW) : CarType {
        return tw
    }

    @Provides
    @Named("four")
    fun tellCar2() : CarType {
        return FW()
    }
}

Error image

Solution

Your class FW does not have the @Inject annotation alongside his constructor. I think it has to be defined this way so Dagger know what to do

class FW @Inject constructor() : CarType {
    override fun whichCar() {
        Log.d("Type", "whichCar: Four wheeler")
    }
}

Also your function tellCar2 should probably be defined in this way :

@Provides
@Named("four"
fun tellCar2(fw: FW) : CartType {
   return fw
}

Since you are using an interface, you could also use @Binds in an abstract module and so you can directly bind the correct implementation of the interface regarding your needs. Check this article : https://medium.com/mobile-app-development-publication/dagger-2-binds-vs-provides-cbf3c10511b5 or this : https://dagger.dev/api/2.21/dagger/Binds.html

Answered By - Fcps