@Binds methods must have only one parameter whose type is assignable to the return type

Question

I am migrating to the new dagger android 2.11

All set up based on the Google blueprint :MVP-Dagger.but I am having this error :

Error:(22, 57) error: @Binds methods must have only one parameter whose type is assignable to the return type

Here in this line :

   @ActivityScoped
    @Binds abstract PresenterFactory<MainContract.Presenter> providePresenterFactory(MainPresenter presenter);

The presenter :

@ActivityScoped
public class MainPresenter extends BasePresenterImpl<MainContract.View>
    implements MainContract.Presenter { public MainPresenter(String s) {..
} ... }

Someone have any idea on how to solve this? Thanks.

Any specific reason why you try to bind `MainPresenter` to `PresenterFactory`? — David Medenjak, Oct 10 '17 at 08:24
It's just a n interface as a Factory that should be implemented to create a presenter for each feature public interface PresenterFactory { @NonNull T create(); } — Mohamed ALOUANE, Oct 10 '17 at 16:09
So your presenter doesn't implement that interface, and it's not supposed to implement the interface, why do you try to bind it as an implementation to said interface? — David Medenjak, Oct 10 '17 at 16:56
Solution: don't try to `@Binds` a class to an interface that it does not implement — EpicPandaForce, Oct 10 '17 at 17:13

David Rawson · Answer 1 · 2018-06-09T00:36:31.840

22

The error message explains everything:

@Binds methods must have only one parameter whose type is assignable to the return type

Your @Binds method has a parameter of MainPresenter. This is not assignable to the return type PresenterFactory<MainContract.Presenter>. In other words, MainPresenter is not an instance of PresenterFactory<MainContract.Presenter>.

The correct syntax for @Binds methods is something like:

@Binds
abstract Abstraction bindAbstration(Concretion concretion)

where concretion is an instance of Abstraction.

Or, in Kotlin:

@Binds
abstract fun bindAbstraction(concretion: Concretion) : Abstraction

@Binds methods are not magic. They bind a type (for instance, an interface) and an implementation of that type that Dagger knows how to provide already.

update

You can convert your @Provides to @Binds with the following steps:

Make sure MainPresenter has an explicit constructor annotated with @Inject and that Dagger 2 can provide the dependencies in the constructor.

Write:

@Binds
abstract MainContract.Presenter bindPresenter(MainPresenter mainPresenter);

edited Jun 09 '18 at 00:36

answered Oct 10 '17 at 20:17

David Rawson

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I see , the Provide one is work just fine. how can i convert it to Binds one ? @ ActivityScoped @ Provides public PresenterFactory providePresenterFactory( DataManager mDataManager) { return MainPresenter::new; } FYI : PresenterFactory is an interface while the presenter it selft extends from BasePresenterImpl – Mohamed ALOUANE Oct 10 '17 at 20:45
Not working because the type of presenter instance is injected like this : @Inject PresenterFactory mPresenterFactory; – Mohamed ALOUANE Oct 11 '17 at 20:51
`abstract Abstraction bindAbstration(Concretion concretion)` this is the ultimate mantra to explain it. – Eido95 Oct 28 '18 at 15:12

score 3 · Answer 2 · answered Oct 23 '19 at 18:13

I had the same exception but in a different situation.

The exception was misleading for me. After adding

kapt {
 correctErrorTypes true 
}

to build.gradle I found the real problem:

error: [ComponentProcessor:MiscError] dagger.internal.codegen.ComponentProcessor was 
unable to process this class because not all of its dependencies could be resolved.
Check for compilation errors or a circular dependency with generated code.

and the hint not all of its dependencies could be resolved helped me to find out that I missed adding implementation project(path: ':repository') to build.gradle of my app module which handles DI stuff.

Hope this help others having same problem.

score -6 · Answer 3 · answered Jul 28 '18 at 18:19

-6

Use @Provides instead of @Binds

answered Jul 28 '18 at 18:19

k4dima

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@Binds methods must have only one parameter whose type is assignable to the return type

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