StaticInjectorError(AppModule)[AppComponent -> DataService]

Question

我一直在学习关于设置平均堆栈的教程，但是当在localhost上运行我的代码时，我会得到一个空白屏幕，错误为'StaticInjectorError(AppModule)DataService -> Http:‘。我花了两天的时间试图找出这个错误，但什么也找不到。

关于我使用的工具的详细信息，角8.3.17，节点v12

data.service.ts

import { Injectable } from '@angular/core';

import { Http, Headers, RequestOptions } from '@angular/http';
import 'rxjs/add/operator/map';


@Injectable()
export class DataService {

  result:any;

  constructor(private _http: Http) { }

  getAccounts() {
    return this._http.get("/api/accounts")
      .map(result => this.result = result.json().data);
  }

}

app.module.ts

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

import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';

// Import the Http Module and our Data Service
import { HttpModule } from '@angular/http';
import { DataService } from './data.service';

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

app.component.ts

import { Component } from '@angular/core';

// Import the DataService
import { DataService } from './data.service';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {

  // Define a users property to hold our user data
  accounts: Array<any>;

  // Create an instance of the DataService through dependency injection
  constructor(private _dataService: DataService) {

    // Access the Data Service's getUsers() method we defined
    this._dataService.getAccounts()
        .subscribe(res => this.accounts = res);
  }
}

Answer 1

您需要在提供者中添加DataService，app.module.ts文件的一部分如下所示

providers: [DataService],

Answer 2

我发现了这个问题，我不得不将dataService添加到提供程序数组中，HttpModule添加到导入中。

  @NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    HttpModule,
    AppRoutingModule
  ],
  providers: [DataService],
  bootstrap: [AppComponent]
})