Angular - Can't resolve all parameters for service (?)

Question

I'm running into an issue with my simple Angular application that I am having trouble debugging. Whenever I try to inject a service into the constructor I get the an error saying Can't resolve all parameters for LoginService (?)

app.component.ts

import { Component, Injector } from '@angular/core';
import { LoginService } from './login.service';

@Component({
    selector: 'app-home',
    template: require('./app.component.html')
})
export default class AppComponent {

constructor(private loginService: LoginService) {}

}

login.service.ts

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

@Injectable()
export class LoginService {

constructor(private http: HttpClient) {
}

login() {
    // Do http requests here
}

}

app.module.ts

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

import { HttpClientModule, HttpClient } from '@angular/common/http';

// Components
import AppComponent from './app.component';

//Services
import { LoginService } from './login.service';

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

Seems to be a problem around the injection of the HttpClient but I cant figure out what exactly.

Any ideas what could be wrong here?

Answer 1

原来是缺少导入！

import 'core-js/es7/reflect';

Answer 2

This can also happen if you've upgraded to Angular 9+ but have disabled Ivy and you're using a library that was compiled with ngc with Ivy turned on. The solution is to upgrade to Ivy or to ask the library owner to produce a non-Ivy build as well.