javascript - 组件中的 Angular 4 HttpClient 无法解析所有参数

Question

我开始学习 Angular 4 并学习了 HTTP 客户端部分。现在我正在尝试从组件进行 http 调用(是的，我知道我应该将它转移到服务，但仍然如此)

但出于某种原因，当我尝试将 HttpClient 注入(inject)我的组件时，出现了下一个错误:

Uncaught Error: Can't resolve all parameters for PromocodeComponent: (?).

这是我的组件的代码:

import { Ticket } from '../../classes/Ticket.class'
import { Component, Input } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'promocode',
  templateUrl: './promocode.template.html',
  styleUrls: ['./promocode.styles.scss']
})
export class PromocodeComponent {
  @Input() ticket: Ticket;
  state: String = "normal";
  promocode: String = "";

   constructor(private http: HttpClient) {}

  promocodeValidate(event): void{
    console.log(this.promocode);
    console.log(event);
    this.http.get('/promocode/asdasda').subscribe(data => {
      console.log(data);
    });
  }
}

还有我的 app.module.ts:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { AppComponent } from './app.component';
import { MovieBadgeComponent } from './movie-badge/movie-badge.component';
import { TicketComponent } from './ticket/ticket.component';
import { PromocodeComponent} from './promocode/promocode.component';
import { FormsModule } from '@angular/forms';
import { HttpClientModule } from '@angular/common/http';


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

Answer 1

事实证明，对我来说，我忘记了服务中的 @Injectable 装饰器。在早期的 Angular (>=2) 中，我记得 @Injectable 是可选的……猜猜是不是？