如何强制Angular 2重新检查验证器？

import { Component } from '@angular/core';
import { FormControl, FormGroup, Validators } from '@angular/forms';

@Component({
  selector: 'app-example',
  template: `
    <form [formGroup]="myForm">
      <input type="text" formControlName="myControl">
      <button (click)="forceValidation()">Force Validation</button>
    </form>
  `
})
export class ExampleComponent {
  myForm: FormGroup;

  constructor() {
    this.myForm = new FormGroup({
      myControl: new FormControl('', Validators.required)
    });
  }

  forceValidation() {
    const control = this.myForm.get('myControl');
    control.updateValueAndValidity();
  }
}