CODEWITHSUNDEEP
androiddagger-2
eC Droid
eC Droid

Reputation: 681

Dagger2 How to perform constructor injection which has dependency of a default constructor

I want to ask how to do the injection of a constructor that doesn't have any parameters. I have come across this problem but unable to find a solution. Here is my repo class

public class UrlsRepository {

    private UrlsSource urlsSource;

    @Inject
    public UrlsRepository(UrlsSource urlsSource){
        this.urlsSource = urlsSource;
    }

    public String getLandingUrl(){
        return urlsSource.getLoginUrl();
    }

    public String[] getDashboardUrls(){
        return urlsSource.getDashboardUrls();
    }
}

Here is the interface

public interface UrlsSource{
    String getLoginUrl();

    String[] getDashboardUrls();
}

and below is the implementation

@Singleton
public class LocalUrlsSource implements UrlsSource {

    @Inject
    public LocalUrlsSource(){}

    @Override
    public String getLoginUrl() {
        return Properties.LOGIN_URL;
    }

    @Override
    public String[] getDashboardUrls() {
        return Properties.DASHBOARD_URLS;
    }
}

Now inside my main activity, I'm injecting UrlsRepository but it's null. Please guide.

public class MainActivity extends Activity implements MainPresenter.View {

    @Inject
    UrlsRepository urlsRepository;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);
    }
}

Upvotes: 1

Views: 309

Answers (1)

Ludvig W
Ludvig W

Reputation: 824

If you wan't to inject interfaces like this you need to create a @Module with a @Binds annotated method like this.

@Module
abstract class UrlModule {

    @Binds
    abstract UrlsSource bindUrlsSource(LocalUrlsSource source);
}

And then you would create a component which uses this module and inject into your activity.

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

    void inject(MainActivity activity);
}

Then initiate the component in your Application.java class and retrieve it inside your activity and call inject(), for example like this.

public final class MainApplication extends Application {

    private static AppComponent appComponent;

    public static AppComponent getAppComponent() {
        return appComponent;
    }

    private static AppComponent createAppComponent(Application application) {
        return DaggerAppComponent.create();
    }

    @Override
    public void onCreate() {
        super.onCreate();

        appComponent = createAppComponent(this);
    }
}

Then you would inject the dependency like this.

public class MainActivity extends Activity implements MainPresenter.View {

    @Inject
    UrlsRepository urlsRepository;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        // Injects this activity.
        MainApplication.getAppComponent().inject(this);
    }
}

Upvotes: 1

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