Dagger 2 Activity context/ApplicationContext modules

Question

I'm struggling with dagger 2 in order to understand how i can pass a context or another according to my needs. - First I have an ApplicationModule annotated @Singleton since it provides hi level objects like the webservice object, the model ..., generally those objects are passed the ApplicationContext (since the y need to live during the whole Application lifetime)

@Singleton
@dagger.Component(modules = {
    AppModule.class
})
public interface AppComponent {
        void inject(MyApp application);
        Model model();
        Context context();<--- should provide the application Context for the Object above (model)
...

the implementation looks like that

@dagger.Module
public class AppModule {

    private final Application app;
    public ApplModule(Application app) {
        this.app = app;
    }

    @Provides
    @Singleton
    Model provideModel(Bus bus) {
        return new Model(bus);
    }

    @Provides
    @Singleton
    Context provideApplicationContext() {
        return app.getApplicationContext();
    }
...

secondly I have an Activity Scope componenet in with I provide the current activity and different views which need a Context.

  @ActivityScope
    @Component(
            dependencies = AppComponent.class
            , modules = {ActivityModule.class}
    )
    public interface ActivityComponent {
        void inject(MyActivity activity);
        Context context(); <---should provide the activity's context
        MyView homeView(); <----takes a Context as a contructor parameter

@Module public class ActivityModule { private final Activity activity;

public ActivityModule(Activity activity) {

    this.activity = activity;
}

@Provides
@ActivityScope
public Activity activity() {
    return activity;
}


@Provides
@ActivityScope
@Named("viewcontext") <----- if I removed this I get an error from Dagger
public Context context() {
    return activity;
}

@Provides
@ActivityScope
MyView provideZeView(Bus bus, Model model) { <---- previously receiving the ApplicationContext as a parameter 
    MyView v = new MyView(activity, bus, model); <---- must pass the activity otherwise passing the Context reveived is the ApplicationContext
    return v;
}

so Here are my questions:

I used scopes in order to have a better "granularity" over what is passed and i still get the applicationContext
If I remove the @Named qulifier i get an error
previously the Views where produced by another module with a dependence to the ActivityModule but still getting the ApplicationContext

Well the point is I am certainly missing something...but I can't figure what, maybe I misundestood the use of Scopes

Considering you have two Context which are pretty much the same, you need to specify @Named("application") and @Named("activity") on them. — EpicPandaForce
Although actually, you can just not add the Context context() to your Component, only to the module, and it'll also work! — EpicPandaForce
Because Dagger fulfills an injection based on type having two methods which provide a Context class can cause an error which is why the nice folks included the @Named() annotation. — fakataha

j2emanue j2emanue · Accepted Answer · 2017-05-30T13:53:06

you can use qualifiers like this. in two separate files define the following:

@Qualifier
@Retention(RetentionPolicy.RUNTIME)
public @interface ActivityContext {
}

@Qualifier
@Retention(RetentionPolicy.RUNTIME)
public @interface ApplicationContext {
}

then in your ActivityModule do this:

@Provides
@ActivityScope
@ActivityContext
public Context context() {
    return activity;
}

and likewise in your appmodule do this:

 @Provides
    @Singleton
@ApplicationContext
    Context provideApplicationContext() {
        return app.getApplicationContext();
    }

now we have a way to ask for whatever type of context we need based on the qualifier @ApplicationContext and @ActivityContext.

so for example in your activity you could do this:

  @Inject @ApplicationContext
    Context c;

which would inject an application context.

and in a module you could do this for example:

  @Provides
    @ActivityScope
    LoginPresenter provideLoginPresenter(@ActivityContext Context context) {
        return new LoginPresenter(context);
    }

to provide an activity context. this is just an example.

Dagger 2 Activity context/ApplicationContext modules

2 Answers