如何在非活动类中注入Context？

Question

I am trying to inject Context in non-activity class. In my case, I am trying to inject in Model class (from MVP pattern). I need Context to get string from resources. The method result() returns Observable which returns ViewModel which is modified API model. ViewModel is used to show in MainActivity. I tried this code, but Context is null, I think that it is not injected.

public class MainActivityModel implements MainActivityMVP.Model {

@Inject
Context context;

private Repository repository;

public MainActivityModel(Repository repository) {

    ((App) getApplication()).getComponent().inject(this); //Cannot resolve getApplication() method :(
    this.repository = repository;

}

@Override
public Observable<List<ViewModel>> result(String username) {

    return repository.getRepositories(username).map(new Func1<List<Repository>, List<ViewModel>>() {
        @Override
        public List<ViewModel> call(List<Repository> repositories) {

            List<ViewModel> viewModelList = new ArrayList<ViewModel>();
            for (Repository repository : repositories) {
                // here Context is null
                viewModelList.add(new ViewModel(context.getString(R.string.repository) + repository.getName()));
            }

            return viewModelList;

        }
    });

}

}

This is Component class, where there is inject(MainActivityModel target) method which I am not able to use inject MainActivityModel because getApplication is not available from non-Activity class:

@Singleton
@Component(modules = {ApplicationModule.class, MainActivityModule.class, GithubApiModule.class})
public interface ApplicationComponent {

    void inject(MainActivity target);
    void inject(MainActivityModel target);

}

I think that Context can be sent via result(String username, Context context) method. But what is the meaning of Dependency Injection if I passing Context as method parameter? Maybe I misunderstood fundamental concept of DI.

So my question: is it possible to inject Context in non-activity class? Or it should be passed as method parameter?

Answer 1

For injecting a Context you will need to write a module with a provides method:

@Module (injects = {MainActivityModel.class})
    public class RootModule {
    private Context context;

    public RootModule(App application) {
        this.context = application.getApplicationContext();
    }

    @Provides
    @Singleton
    Context provideContext() {
        return context;
    }
}

In your custom App class:

public class App extends Application {
    public ObjectGraph objectGraph;

    @Override
    public void onCreate() {
        super.onCreate();
        objectGraph = ObjectGraph.create(getInjectionModule());
    } 

    protected Object getInjectionModule() {
        return new RootModule(this);
    }
}

And inject in model's constructor:

public MainActivityModel(Repository repository) {

    ((App) getApplication()).objectGraph.inject(this); 
    this.repository = repository;

}