Dagger2 Found Dependency Cycle Android

Question

Im learning and newer to Dagger2 and stuck in the issue where I need to use both @Provides and @Binds in a Module. but its giving error

[Dagger/DependencyCycle] Found a dependency cycle:
 public interface CarComponent{
        ^
      com.stupido.daggertutorial.Engine is injected at
          com.stupido.daggertutorial.CarModule.bindsEngine(arg0)
      com.stupido.daggertutorial.Engine is injected at
          com.stupido.daggertutorial.CarModule.providesCar(engine, …)
      com.stupido.daggertutorial.Car is requested at
          com.stupido.daggertutorial.CarComponent.getCar() 

before I was using @Provides it worked fine but with combination I get above issue.

Component

@Component(modules = CarModule.class)
 public interface CarComponent{
    //constructor injection
    Car getCar();
    
}

Module

@Module
public abstract class CarModule {
    @Binds
    abstract Wheels bindsWheels(Wheels wheels);

    @Binds
    abstract Engine bindsEngine(Engine engine);

    @Provides
     static Car providesCar(Engine engine,Wheels wheels){
        return new Car(wheels,engine);
    }
}

Activity

public class MainActivity extends AppCompatActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        CarComponent carComponent = DaggerCarComponent.create();
        Car car = carComponent.getCar();
    }
}

Answer 1

@Binds is usually for the case when you have some inherited class and its interface and you want dagger to know this and be able to inject the interface. Usually you'd have

@Binds
abstract Engine bindsEngine(DieselEngine dieselEngine);

and then you can just inject engine without knowing the implementation detail (it's diesel engine).

In your case, if you remove both @Binds methods, it should start working (if there's no other issue).

Answer 2

You are using @Binds in the wrong way. Please read their documentation.

A @Binds method:
Must have a single parameter whose type is assignable to the return type. The return type declares the bound type (just as it would for a @Provides method) and the parameter is the type to which it is bound.

You have to change @Binds to @Provides.