不能用组件角度6绑定表单组

Question

这是一个带有angular6的简单表单组：

import { Component, OnInit } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/observable/interval';
import { Subscription } from 'rxjs';
import { FormGroup, FormBuilder } from '@angular/forms';
import { User } from '../../commun/model/user.model';

@Component({
  selector: 'app-newcontact',
  templateUrl: './newcontact.component.html',
  styleUrls: ['./newcontact.component.css']
})
export class NewcontactComponent implements OnInit {

  userForm: FormGroup;

  constructor(private formBuilder: FormBuilder) { }

  ngOnInit() {
    this.initForm();
  }

  initForm() {
    this.userForm = this.formBuilder.group({
      firstName: '',
      lastName: '',
      email: ''
    });
}

onSubmitForm() {
  const formValue = this.userForm.value;
  const newUser = new User(
    formValue['firstName'],
    formValue['lastName'],
    formValue['email']
  );

}

   <form [formGroup]="userForm" (ngSubmit)="onSubmitForm()">
    </form>

这是我的模特用户：

export class User {
  constructor(
    public firstName: string,
    public lastName: string,
    public email: string
  ) {}
}

我有一个错误，firebug说无法绑定表单组，我在我的代码片段中忘记了什么？ 使用visual sudio，我没有错误。

谢谢你的回复