Export service from another module in Angular 2
<p>I'm trying to create a reusable service within a separate module, much like <a href="https://angular.io/styleguide" rel="nofollow noreferrer">Angular 2's styleguide</a>. However I get an error when I trying to use that service within another service:</p>

<p><code>Uncaught Error: Can't resolve all parameters for AttendanceSummaryService:</code></p>

<p>Here is my core module:</p>

<pre><code>import { NgModule, Optional, SkipSelf } from '@angular/core';
import { CommonModule } from '@angular/common';
import { throwIfAlreadyLoaded } from './module-import-guard';
import { HttpClientService } from './httpClient.service';
import { HttpModule } from '@angular/http';

@NgModule({
    imports: [
        CommonModule,
        HttpModule
    ],
     exports: [],
     declarations: [],
     providers: [HttpClientService]
})
export class CoreModule {
    constructor( @Optional() @SkipSelf() parentModule: CoreModule) {
        throwIfAlreadyLoaded(parentModule, 'CoreModule');
    }
}
</code></pre>

<p>My <code>HttpClientService</code>:</p>

<pre><code>import { Injectable } from '@angular/core';
import { Http, Headers } from '@angular/http';

@Injectable()
export class HttpClientService {

    constructor(private http: Http) { }

    createAuthorizationHeader(headers: Headers) {
        headers.append('Authorization', 'Bearer ' + '');
    }

    get(url) {
        let headers = new Headers();
        this.createAuthorizationHeader(headers);
        return this.http.get(url, {
            headers: headers
        });
    }

    post(url, data) {
        let headers = new Headers();
        this.createAuthorizationHeader(headers);
        return this.http.post(url, data, {
            headers: headers
        });
    }
}
</code></pre>

<p>And my app.module which imports the core module:</p>

<pre><code>import { NgModule, ApplicationRef } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { HttpModule } from '@angular/http';
import { AppComponent } from './app.component';
import { AttendanceSummaryService } from './home/attendance-summary.service';
import { CoreModule } from './core/core.module';
import { HttpClientService } from './core/httpClient.service';

import {FormControl, FormGroup,  ReactiveFormsModule} from '@angular/forms';


@NgModule({
  bootstrap: [AppComponent],
  declarations: [
    AppComponent,
    AttendanceSummaryComponent,
  ],
  imports: [
    BrowserModule,
    FormsModule,
    ReactiveFormsModule,
    HttpModule,
    CoreModule
  ],
  providers: [
    HttpClientService,
    AttendanceSummaryService    

  ]
})
export class AppModule {
  constructor(public appRef: ApplicationRef) { }
}
</code></pre>

<p>And the service which consumes the <code>HttpClientService</code>:</p>

<pre><code>import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Rx';
import { AttendanceSummary } from './attendance-summary.model';
import { Http, Response, Headers, RequestOptions } from '@angular/http';
import { HttpClientService } from '../core/httpClient.service';


Injectable()
export class AttendanceSummaryService {

    private apiBaseUrl = '/api/v1/agency/attendances/';
    constructor(private http: HttpClientService) { }
}
</code></pre>

<p>Any ideas?</p>

<p>Thanks.</p>