How to pass context to repository in MVP pattern

Question

I have been learning and integrating MVP pattern, and have few questions.

What i have understand from this diagram, is that

Activity will create instance of Presenter, and pass its reference and model object to the presenter

MainPresenter mainPresenter = new MainPresenter(this, new MainModel());

Next if presenter need to store or get any data from local preference or remotely, it will ask model.

And then model will ask repository for storing and retrieving data.

I followed few tutorials and this is how i implement the pattern.

Interface

public interface MainActivityMVP {

    public interface Model{

    }

    public interface View{
        boolean isPnTokenRegistered();
    }

    public interface Presenter{

    }
}

Activity

MainPresenter mainPresenter = new MainPresenter(this, new MainModel());
mainPresenter.sendDataToServer();

Presenter

public void sendDataToServer() {

    //  Here i need to ask `model` to check 
        do network operation and save data in preference
}

Now the issue is i need context to access sharedPreference, but i have not passed context anywhere. I also don't want to use static context. I want to know the proper way of passing context to MVP pattern.

@quicklearner, I don't want to use this approach, is there any other way? or application class is the only possible way? — Taha Kirmani, May 03 '18 at 12:31
its a better approach i think :), it wont return null untill the app is killed — Quick learner, May 03 '18 at 12:31
Lets wait for some other answers, i will go with this approach, if doesn't get any other solution :) .Thanks — Taha Kirmani, May 03 '18 at 12:38

Levi Moreira · Accepted Answer · 2018-05-03T12:50:52.697

2

Well, the best approach is to wrap your preferences class in a helper class and use Dagger to inject it anywhere you need, that way your presenter/model doesn't need to know about the Context. For example, I have an application module that provides a variaty of singletons, one of them is my Preferences Util class that deals with the Shared preferences.

@Provides
@Singleton
public PreferencesUtil providesPreferences(Application application) {
    return new PreferencesUtil(application);
}

Now, anytime I want to use it I just @Inject it:

@Inject
PreferencesUtil prefs;

I think it's worth the learning curve as your MVP project will be more decoupled.

However, if you're willing to forget about the "Presenter doesn't know about Android context" rule you can simply add a getContext method to your view interface and get the Context from the view:

public interface MainActivityMVP {

    public interface Model{

    }

    public interface View{
        boolean isPnTokenRegistered();
        Context getContext();
    }

    public interface Presenter{

    }
}

And then:

public void sendDataToServer() {
      Context context = view.getContext();
}

I've seen some people implement MVP like this, but my personal preference is to use Dagger.

You can also use the application conext, as suggested in the comments.

edited May 03 '18 at 12:50

answered May 03 '18 at 12:40

Levi Moreira

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Thanks @Levi, i read somewhere that there shouldn't be any reference of `context` in `Presenter` If i don't go with dagger and follow the second approach, i will have context reference in `Presenter`, and i will be passing it to model from presenter. – Taha Kirmani May 03 '18 at 12:46
Why not dagger? I tried but unable to find beginner level tutorial that explain dagger2 in detail, or may be i am just too dumb :( – Taha Kirmani May 03 '18 at 12:47
Yeah, the learning curve is pretty steep, it's nothing to do with you being dumb, don't worry. But regarding the answer AFAIK you have three options 1) Use dagger, 2) Deal with context inside presenter 3)Use application context – Levi Moreira May 03 '18 at 12:49
1

Thanks @Levi, I will try to look into Dagger, but for now the most suitable option i guess is `Use application context`. With this option, presenter will not have any reference of context, and repository will use it when it needs, and when i learn `dagger`, i will upgrade these classes. I was little afraid, if using `application context` is the right approach or not. – Taha Kirmani May 03 '18 at 13:01
1

All righto :) Good luck with dagger, it's huge but once you get the grasp (and you will at some point) it's really helpful :) – Levi Moreira May 03 '18 at 13:17

YorchSircam · Answer 2 · 2018-05-04T22:27:44.063

You are not so far of what you are looking for. You have a model interface, so you have a class that implements this interface, maybe something like this:

MainModel implements MainActivityMVP.Model{
    SharedPreferences mPrefs;

    MainModel(Context context){
        mPrefs =context.getSharedPreferences("preferences",Context.MODE_PRIVATE);
    }
}

So, you only need to pass that reference to your presenter, but instead of receive an MainModel class, you can receive an MainActivityMVP.Model instead.

MainActivityMVP.Presenter mainPresenter = new MainPresenter(this, new MainModel(getContext()));

MainPresenter implements MainActivityMVP.Presenter{

     MainActivityMVP.View mView;
     MainActivityMVP.Model mModel;

     MainPresenter(MainActivityMVP.View view, MainActivityMVP.Model model){
           mView = view;
           mModel = model;
     }
}

In this way you don't have any context reference into your presenter, and the reference is into your MainModel and not into your MainActivityMVP.Model.

Add any public method into your presenter/view/model interfaces. You should have something like this:

public interface MainActivityMVP {

    public interface Model{
        void saveOnSharedPreferences();
    }

    public interface View{
        boolean isPnTokenRegistered();
    }

    public interface Presenter{
        void sendDataToServer();
    }
}

How to pass context to repository in MVP pattern

2 Answers2