angular - Angular 6 中模块声明的意外值

Question

In this plunk我有一个 Angular 6 模块，其中包含包装 HttpClient 的相关服务。该模块由应用模块导入，主要应用组件调用服务。

问题是我收到以下错误:

Unexpected value 'MyHttpService' declared by the module 'CoreServiceModule'. Please add a @Pipe/@Directive/@Component annotation

我检查了所有的导入和声明，没有发现问题。哪里出错了？

模块:

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { HttpClientModule } from '@angular/common/http';
import { MyHttpService } from './http.service';

@NgModule({
  imports: [
    CommonModule,
    HttpClientModule
  ],
  declarations: [
    MyHttpService
  ],
  exports: [
    MyHttpService
  ]
})
export class CoreServiceModule {}

和服务:

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs/Observable';

@Injectable({
  providedIn: 'root'
})
export class MyHttpService {

  constructor(public httpx: HttpClient) {
        console.log("In the HttpClient constructor - " + this.httpx) 
  }

  call () {
        let data = { x: 1 };
        this.httpx.post('response.json', data).subscribe(result => {
            console.log("Http result = " + result);
          }, error => console.log('There was an error: '));
    }
}

Answer 1

通常如错误所述，services,pipes 应该在您的模块的提供者下，remove from declarations 并将其添加到 providers,

@NgModule({
  imports: [
    CommonModule,
    HttpClientModule
  ]
  declarations : [],
  providers:[ 
     MyHttpService
  ],
  exports: [

  ]
})