Angular6：未捕获的错误：无法解析HttpService的所有参数：（？）

Question

I am trying to read data from a web service using the HttpClientModule . I have created my own class HttpService where I want to do all the operations related to http. However, I am getting an error when creating the HttpService object.

Code in my main class:

httpS:HttpService;
this.httpS.getHttpData(this.urlS).subscribe(data => {
this.posts = data
});

HttpService class:

import { Observable } from 'rxjs';
import { Post } from '../Interfaces/Post';
import { HttpClient } from '@angular/common/http';

export class HttpService {

constructor(private httpC: HttpClient) { }

getHttpData(urlString: string): Observable<Post[]> {
  console.log(urlString);
  return this.httpC.get<Post[]>(urlString);
}
}

AppModule.ts:

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

import { AppComponent } from './app.component';
import { HttpService } from './classes/HttpService';

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

Would be very grateful for everyone who can help me with this problem :)

Answer 1

You need to add @Injectable() to your HttpService , since you are using Dependency Injection (HttpClient) in your service

@Injectable()

export class HttpService {

constructor(private httpC: HttpClient) { }

getHttpData(urlString: string): Observable<Post[]> {
  console.log(urlString);
  return this.httpC.get<Post[]>(urlString);
}
}

EDIT :

Well, as @ AJT_82 pointed out, You should add HttpService as a DI in your component, instead of creating a direct reference httpS:HttpService .

Add this to your component

constructor (private httpS : HttpService) { 
}