如何在Angular2中为模型驱动表单编写自定义验证器指令？

import { Directive } from '@angular/core';
import { NG_VALIDATORS, Validator, AbstractControl, ValidationErrors } from '@angular/forms';

@Directive({
  selector: '[customValidator]',
  providers: [{ provide: NG_VALIDATORS, useExisting: CustomValidatorDirective, multi: true }]
})
export class CustomValidatorDirective implements Validator {
  static validate(control: AbstractControl): ValidationErrors | null {
    // 在这里编写自定义的验证逻辑
    // 如果验证通过，返回 null；否则返回一个包含错误信息的对象
    return null;
  }
}

<form>
  <input type="text" name="myField" [(ngModel)]="myValue" customValidator>
  <div *ngIf="myForm.controls.myField.errors">验证错误：{{ myForm.controls.myField.errors | json }}</div>
</form>

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

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

  constructor() {
    this.myForm = new FormGroup({
      myField: new FormControl('', CustomValidatorDirective.validate)
    });
  }
}