Angular FormGroup在ngAfterViewInit上变得无效

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

@Component({
  selector: 'app-example',
  template: `
    <form [formGroup]="myForm">
      <!-- form controls here -->
    </form>
  `,
})
export class ExampleComponent implements OnInit {
  myForm: FormGroup;

  ngOnInit() {
    this.myForm = new FormGroup({
      // form controls initialization
    });
  }
}