将服务从Angular2重写为Angular6“模块'AppModule'声明了意外的模块'HttpClientModule'

Question

我试图重写在Angular 2中可以正常工作的服务，并且试图重写Angular 6。

这是服务：

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { environment } from '../../environments/environment';
import {Cluster} from "./cluster";
import {map} from "rxjs/internal/operators";


@Injectable({
  providedIn: 'root'
})
export class FullDataService {
  private headers = new Headers({'Content-Type': 'application/json'});

  constructor(private http: HttpClient) {}

  getClusters() {
    const url = environment.apiUrl + '/api/v1/clusters';
    return this.http.get(url).pipe(map(res => <Cluster[]>res));
  }
}

这是我的app.models.ts：

import { BrowserModule } from '@angular/platform-browser';
import { HttpClientModule, HttpClient } from '@angular/common/http';
import { NgModule } from '@angular/core';
import * as $ from 'jquery';

import { ContentHeaderComponent} from './content-header/content-header.component';
import { ContentHeaderService} from './content-header/content-header.service';

import { AppComponent } from './app.component';
import { HomeComponent } from './home/home.component';
import { AppRoutingModule } from './app-routing.module';
import { FullDataComponent } from './full-data/full-data.component';
import {FullDataService} from "./full-data/full-data.service";


@NgModule({
  declarations: [
    AppComponent,
    HttpClientModule,
    HomeComponent,
    ContentHeaderComponent,
    FullDataComponent,
    HttpClient,
   HttpClientModule
  ],
  imports: [
    BrowserModule,
    AppRoutingModule
  ],
  providers: [
    ContentHeaderService,
    FullDataService,
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }

$(document).ready(function() {
    $('#base-header .toggle-menu').click(function() {
        $('#base-sidebar').toggleClass('sidebar--hidden');
    });

    $('nav .sidebar__drawer > a').click(function() {
        $(this).parent().toggleClass('sidebar__drawer--opened');
    });
});

当我尝试在浏览器中加载我的应用程序时，在控制台日志中收到此错误：

compiler.js:215 Uncaught Error: Unexpected module 'HttpClientModule' declared by the module 'AppModule'. Please add a @Pipe/@Directive/@Component annotation.
    at syntaxError (compiler.js:215)
    at compiler.js:10524
    at Array.forEach (<anonymous>)
    at CompileMetadataResolver.push../node_modules/@angular/compiler/fesm5/compiler.js.CompileMetadataResolver.getNgModuleMetadata (compiler.js:10506)
    at JitCompiler.push../node_modules/@angular/compiler/fesm5/compiler.js.JitCompiler._loadModules (compiler.js:22567)
    at JitCompiler.push../node_modules/@angular/compiler/fesm5/compiler.js.JitCompiler._compileModuleAndComponents (compiler.js:22548)
    at JitCompiler.push../node_modules/@angular/compiler/fesm5/compiler.js.JitCompiler.compileModuleAsync (compiler.js:22508)
    at CompilerImpl.push../node_modules/@angular/platform-browser-dynamic/fesm5/platform-browser-dynamic.js.CompilerImpl.compileModuleAsync (platform-browser-dynamic.js:143)
    at PlatformRef.push../node_modules/@angular/core/fesm5/core.js.PlatformRef.bootstrapModule (core.js:4199)
    at Object../src/main.ts (main.ts:11)

我究竟做错了什么？

谢谢！

更新：感谢您的帮助。 现在，我在运行服务时收到以下错误消息：

No 'Access-Control-Allow-Origin' header is present on the requested resource.

那是怎么回事？

Answer 1

从声明中删除HttpClientModule ，它应该在import下

 declarations: [
    AppComponent,
    HttpClientModule,
    HomeComponent,
    ContentHeaderComponent,
    FullDataComponent,
    HttpClient,
    HttpClientModule // remove this from here
  ],

Answer 2

HttpClientModule应该添加在imports数组而非声明数组中。

import数组用于导入模块，例如Br​​owserModule，AppRoutingModule，HttpClientModule

声明数组适用于您的AppComponent，HomeComponent，ContentHeaderComponent，FullDataComponent，HttpClient

@NgModule({
  declarations: [
    AppComponent,
    HomeComponent,
    ContentHeaderComponent,
    FullDataComponent,
    HttpClient
  ],
  imports: [
    BrowserModule,
    AppRoutingModule,
    HttpClientModule
  ],
  providers: [
    ContentHeaderService,
    FullDataService,
  ],
  bootstrap: [AppComponent]
})

对于没有'Access-Control-Allow-Origin'头，请求的资源上不存在。

尝试在服务器端添加标题

header('Access-Control-Allow-Origin: *');
header('Access-Control-Allow-Methods: POST');
header('Content-Type: application/json; Charset=UTF-8');