angular material单选按钮默认选中，不验证表单

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

@Component({
  selector: 'app-example',
  templateUrl: './example.component.html',
  styleUrls: ['./example.component.css']
})
export class ExampleComponent implements OnInit {
  form: FormGroup;
  
  constructor() { }
  
  ngOnInit() {
    this.form = new FormGroup({
      radioButton: new FormControl('option1') // 设置默认选中的值为'option1'
    });
  }
}

<form [formGroup]="form">
  <mat-radio-group formControlName="radioButton">
    <mat-radio-button value="option1">Option 1</mat-radio-button>
    <mat-radio-button value="option2">Option 2</mat-radio-button>
    <mat-radio-button value="option3">Option 3</mat-radio-button>
  </mat-radio-group>
</form>

import { Validators } from '@angular/forms';

// ...

this.form = new FormGroup({
  radioButton: new FormControl('option1', Validators.required)
});