angular 5中ng-multiselect-dropdown的验证

<form [formGroup]="myForm">
  <ng-multiselect-dropdown
    [placeholder]="'Select options'"
    [data]="dropdownOptions"
    formControlName="selectedOptions"
  ></ng-multiselect-dropdown>
</form>

import { Component, OnInit } from '@angular/core';
import { FormGroup, FormControl, 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;
  dropdownOptions: any[] = [
    { id: 1, name: 'Option 1' },
    { id: 2, name: 'Option 2' },
    { id: 3, name: 'Option 3' }
  ];

  ngOnInit() {
    this.myForm = new FormGroup({
      selectedOptions: new FormControl(null, Validators.required)
    });
  }
}

<form [formGroup]="myForm">
  <ng-multiselect-dropdown
    [placeholder]="'Select options'"
    [data]="dropdownOptions"
    formControlName="selectedOptions"
  ></ng-multiselect-dropdown>
  <div *ngIf="myForm.get('selectedOptions').invalid && myForm.get('selectedOptions').touched">
    Please select at least one option.
  </div>
</form>