角度数据服务无法解析参数

我使用的是角V.4.2.4。当我试图从API获取数据时,我得到了一个似乎找不到的错误。API在我自己的机器上,并且正在以邮递员的方式返回数据。我得到的错误是:

Can't resolve all parameters for DataService

以下是我认为有助于发现错误的文件:

应用程序模块

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { HttpClientModule } from '@angular/common/http';    

import { AppComponent } from './app.component';
import { ProductComponent } from './shop/product.component';
import { DataService } from './shared/dataService';

@NgModule({
    declarations: [       
        AppComponent,
        ProductComponent
    ],
    imports: [
        BrowserModule,
        HttpClientModule
    ],
    providers: [DataService],
    bootstrap: [AppComponent]
})
export class AppModule { }

数据服务

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import 'rxjs/add/operator/map';
import { Product } from './product';

Injectable()
export class DataService {

    constructor(private http: HttpClient) { }

    public products: Product[] = [];

    loadProducts(): Observable<boolean>{
        return this.http.get('/api/products')
            .map((data: any[]) => {
                this.products = data;
                return true;
            })
    }
}

产品.组件

import { Component, OnInit } from "@angular/core";
import { DataService } from '../shared/dataService';
import { Product } from '../shared/product';  


@Component({
    selector: "product-list",
    templateUrl: "productList.component.html",
    styleUrls: []
})

export class ProductComponent implements OnInit {

    constructor(private data: DataService) { }

    public products: Product[] = [];

    ngOnInit(): void {
        this.data.loadProducts()
            .subscribe(success => {
                if (success) {
                    this.products = this.data.products;
                }
            });
    }
}

告诉我你还想看什么。谢谢你的帮助。