Angular 6:如何通过索引插值向动态反应表单添加验证？

import { FormsModule, ReactiveFormsModule } from '@angular/forms';

<form [formGroup]="myForm">
  <div formArrayName="dynamicControls">
    <div *ngFor="let control of dynamicControls.controls; let i = index">
      <input type="text" [formControlName]="i">
    </div>
  </div>
</form>

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

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

  constructor(private formBuilder: FormBuilder) { }

  ngOnInit() {
    this.myForm = this.formBuilder.group({
      dynamicControls: this.formBuilder.array([])
    });
  }

  get dynamicControls() {
    return this.myForm.get('dynamicControls') as FormArray;
  }

  addControl() {
    const control = this.formBuilder.control('', Validators.required);
    this.dynamicControls.push(control);
  }
}

<button (click)="addControl()">Add Control</button>

addControl() {
  const control = this.formBuilder.control('', Validators.required);
  this.dynamicControls.push(control);
}