Angular 2错误 - 'HttpService'类型中不存在属性'getData'

Question

学习本教程时遇到错误：https://metanit.com/web/angular2/6.1.php

错误：（类型'HttpService'上不存在属性'getData'）

服务文件：

import {Injectable} from '@angular/core';
import {Http} from '@angular/http';    
@Injectable()
export class HttpService{    
    constructor(private http: Http){ }    
    getData(){
        return this.http.get('user.json')
    }
}

app模块

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { HttpModule } from '@angular/http';    
import { AppComponent } from './app.component';   
@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    FormsModule,
    HttpModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

组件文件：

import { Component, OnInit } from '@angular/core';
import { Response} from '@angular/http';
import { HttpService} from './http.service';
import {User} from './user';    
@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css'],
  providers:[HttpService]
})
export class AppComponent implements OnInit{
  title = 'app works!';
  user: User;    
  constructor(private httpService: HttpService){}    
  ngOnInit(){    
    this.httpService.getData().subscribe((data: Response) => this.user=data.json());
  }
}