dagger2 constructor injection how to provide dependency without module

Question

I've read that constructor injections don't require a module. So I have this questions.

If I have this constructor injection:

private Model realmModel;

@Inject
public MainActivityPresenter(Model realmModel) {
    this.realmModel = realmModel;
}

and this component:

@Singleton
@Component(modules = {AppModule.class})
public interface AppComponent {


    Model realmModel();
    void inject(MainActivity activity);


}

if in my MainActivity I do it:

((MyApp)getApplication()).createAppComponent().inject(this);

how could I pass the realmModel parameter to the presenter constructor injection?

EDIT: this is the model:

 Presenter presenter;

 @Inject
 public RealmModel(Presenter presenter) {
    this.presenter = presenter;

}

Thanks

You have a cyclic dependency here and you should try to get rid of it. Your model depends on the presenter and the presenter depends on the model. Hence you will not be able to constructor inject either, since neither can be created without the other being created first. Does your model really need to keep a reference to the presenter? — David Medenjak, May 22 '17 at 19:55
@DavidMedenjak not sure, I could make a callback to handle the results to the presenter, but without it this works? — nani, May 23 '17 at 10:42

Jileshl · Answer 1 · 2017-07-17T05:18:21.253

Three ways to solve this problem

1) Give a module which does the provide of the Relam Model

 @Provides
 @Singleton
 public Model providesRealmModel() {
     return new Model();
 }

2) Make your RelamModel class also constructor injected

class Model {
   @Inject
   public Model() {}
}

The Trick in construction injection is all its dependencies should also be constuctor injeceted then it would work fine. (From experience your model would need application context. look at the 3 option for ways to implement external Dependencies

3) Provide Model as external dependency.

 @Module
 public class ModelModule {
    private Model relamModel;
    public ModelModule(Model relamModel) {
       this.relamModel = relamModel
    }
 }

@Component(module={ModelModule.class}) 
public interface ApplicationComponent {
}

Take a look at the series of videos from twisted eqautions these were my first video tutorial on dagger2. I found it really helpful. Hope it helps you too https://www.youtube.com/watch?v=Qwk7ESmaCq0

score 0 · Answer 2 · answered May 22 '17 at 15:36

0

You have two choices:

use a module with a provide method
annotate the constructor of Model with @Inject, doing that when you pass realmModel in the presenter contructor, the model constructor will be called.

I prefer to use modules, but that's just my opinion.

answered May 22 '17 at 15:36

Matias Elorriaga

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so now you need to provide a Presenter.. same steps as with Model – Matias Elorriaga May 22 '17 at 15:42
Presenter is the interface that MainActivityPresenter implements..it's possible to do it? – nani May 22 '17 at 15:43
so, your mainActivityPresenter has a model, that has a presenter.. mm sounds like you need to work on the design of that.. – Matias Elorriaga May 22 '17 at 15:52
the model has the reference to the presenter to give back data...otherwise how presenter could be update the view? – nani May 22 '17 at 15:54
you can use an interface, or even an event bus.. I recommend using an interface, take a loot at this: https://github.com/matoelorriaga/pokemon. Check the view-presenter-interactor (interactor is what you call model) – Matias Elorriaga May 22 '17 at 15:56
the presenter should implement an interface called inside the "model" – Matias Elorriaga May 22 '17 at 15:58
so it's the Interactor what do you mean? – nani May 22 '17 at 16:03

dagger2 constructor injection how to provide dependency without module

2 Answers2