如何根据angular 6中的条件验证表单？

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

@Component({
  selector: 'app-your-component',
  templateUrl: './your-component.component.html',
  styleUrls: ['./your-component.component.css']
})
export class YourComponent {
  form: FormGroup;

  constructor(private formBuilder: FormBuilder) {
    this.form = this.formBuilder.group({
      // 在这里定义表单控件和验证规则
    });
  }
}

<form [formGroup]="form">
  <div>
    <label for="name">姓名：</label>
    <input type="text" id="name" formControlName="name">
    <div *ngIf="form.get('name').invalid && (form.get('name').dirty || form.get('name').touched)">
      <div *ngIf="form.get('name').errors.required">姓名是必填项。</div>
      <div *ngIf="form.get('name').errors.minlength">姓名长度不能少于2个字符。</div>
    </div>
  </div>

  <div>
    <label for="age">年龄：</label>
    <input type="number" id="age" formControlName="age">
    <div *ngIf="form.get('age').invalid && (form.get('age').dirty || form.get('age').touched)">
      <div *ngIf="form.get('age').errors.required">年龄是必填项。</div>
      <div *ngIf="form.get('age').errors.min">年龄必须大于等于0。</div>
      <div *ngIf="form.get('age').errors.max">年龄不能超过150。</div>
    </div>
  </div>

  <div>
    <label for="email">邮箱：</label>
    <input type="email" id="email" formControlName="email">
    <div *ngIf="form.get('email').invalid && (form.get('email').dirty || form.get('email').touched)">
      <div *ngIf="form.get('email').errors.required">邮箱是必填项。</div>
      <div *ngIf="form.get('email').errors.email">请输入有效的邮箱地址。</div>
    </div>
  </div>

  <button type="submit" [disabled]="form.invalid">提交</button>
</form>