Angular4：注入Service后组件消失

Question

我在 Angular 4 中遇到了关于 Components 和 Services 的问题。所以我得到了 CustomerComponent:

@Component({
selector: 'app-customer',
templateUrl: './customer.component.html',
styleUrls: ['./customer.component.css']
})
export class CustomerComponent implements OnInit {

customers: Customer[] = [];
constructor() { }

和 Customer Model:

export class Customer {
constructor(
public id: number,
public firstName: string,
public lastName: string
) {  }
}

和 CustomerService:

@Injectable()
export class CustomerService {

private customersUrl = 'http://localhost:9090/customer';
constructor(private http: Http) { }

// Get all customers
getCustomers(): Promise<Customer[]> {
return this.http.get(this.customersUrl)
  .toPromise()
  .then(response => response.json() as Customer[])
  .catch(this.handleError);
}

现在我想在 AppComponent 中显示 CustomerComponent。它通过添加 <app-customer></app-customer> 显示：customer works.

但是当我像这样将 CustomerService 添加到 CustomerComponent 的构造函数中时：

 constructor(private customerService: CustomerService) { }

customer works 不再显示，我也没有在控制台中收到错误消息。所以我不知道问题是什么。有人可以帮忙吗？谢谢

Answer 1

将您的服务添加到应用程序模块。

providers: [
    CustomerService
  ],

Answer 2

我发现了问题所在。我忘记在 AppModule 中导入 HttpModule。但是我仍然不知道为什么我在任何地方都没有看到错误...

Angular4：注入Service后组件消失

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