如何在表单之外检查angular中输入的有效性，而不检查ng-invalid？

<form #myForm="ngForm">
  <input type="text" name="myInput" [(ngModel)]="myValue" required>
</form>

<button (click)="checkValidity()">检查有效性</button>

import { Component } from '@angular/core';

@Component({
  selector: 'app-my-component',
  templateUrl: './my-component.component.html',
  styleUrls: ['./my-component.component.css']
})
export class MyComponent {
  myValue: string;

  checkValidity() {
    const control = this.myForm.controls['myInput'];
    if (control.valid) {
      console.log('输入有效');
    } else {
      console.log('输入无效');
    }
  }
}

<form [formGroup]="myForm">
  <input type="text" formControlName="myInput" required>
</form>

<button (click)="checkValidity()">检查有效性</button>

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

@Component({
  selector: 'app-my-component',
  templateUrl: './my-component.component.html',
  styleUrls: ['./my-component.component.css']
})
export class MyComponent implements OnInit {
  myForm: FormGroup;

  constructor(private formBuilder: FormBuilder) { }

  ngOnInit() {
    this.myForm = this.formBuilder.group({
      myInput: ['', Validators.required]
    });
  }

  checkValidity() {
    const control = this.myForm.get('myInput');
    if (control.valid) {
      console.log('输入有效');
    } else {
      console.log('输入无效');
    }
  }
}