将服务从 Angular2 重写为 Angular6 "由模块 'AppModule' 声明的意外模块 'HttpClientModule'

Question

我试图重写一个在 Angular 2 中运行良好的服务，我试图用 Angular 6 重写。

以下是服务：

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));
}
}

这是我的应用程序.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，我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)

我做错了什么？

谢谢！

更新：感谢您的帮助。 现在，当我的服务运行时，我收到此错误消息：

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

这是怎么回事？

Answer 1

从声明中删除HttpClientModule，它应该在导入下

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

Answer 2

HttpClientModule应该在导入数组而不是声明数组中添加。

imports 数组用于导入模块，如 BrowserModule、AppRoutingModule、HttpClientModule

声明数组用于您的应用程序组件、主页组件、 ContentHeaderComponent， FullDataComponent， HttpClient

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

对于请求的资源上不存在"访问控制允许源"标头。

尝试在服务器端添加标头

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