@Module
public class AppModule {

    private Context appContext;

    public AppModule(Context appContext){
        this.appContext = appContext;
    }

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


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

    void inject(MainActivity act);
}

public class App extends Application {
    public static AppComponent appCompanent;
    onCreate() {
        appComponent = DaggerAppComponent.builder()
                .appModule(AppModule(this))
                .build();
    }
}

public class MainActivity extends Activity {

    @Inject
    Context appContext;

    @Override
    void onCreate() {
        App.appCompanent.inject(this);
    }
}