Angular 9 FormArray条件验证-订阅问题

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

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

  ngOnInit() {
    this.myForm = new FormGroup({
      items: new FormArray([])
    });

    // 订阅FormArray的valueChanges事件
    this.myForm.get('items').valueChanges.subscribe((value) => {
      // 根据特定条件对表单控件进行验证
      const formArray = this.myForm.get('items') as FormArray;
      formArray.controls.forEach((control) => {
        if (control.value === 'example') {
          control.setErrors({ invalid: true });
        } else {
          control.setErrors(null);
        }
      });
    });
  }

  addItem() {
    const formArray = this.myForm.get('items') as FormArray;
    formArray.push(new FormControl(''));
  }

  removeItem(index: number) {
    const formArray = this.myForm.get('items') as FormArray;
    formArray.removeAt(index);
  }
}

<form [formGroup]="myForm">
  <div formArrayName="items">
    <div *ngFor="let item of myForm.get('items').controls; let i = index">
      <input type="text" [formControlName]="i">
      <button (click)="removeItem(i)">Remove</button>
    </div>
  </div>
  <button (click)="addItem()">Add</button>
</form>