Angular2在formGroup上取消订阅valueChanges

import { Component, OnInit, OnDestroy } from '@angular/core';
import { FormGroup, FormBuilder } from '@angular/forms';
import { Subscription } from 'rxjs';

@Component({
  selector: 'app-my-form',
  template: `
    <form [formGroup]="myForm">
      <!-- 表单控件 -->
    </form>
  `,
})
export class MyFormComponent implements OnInit, OnDestroy {
  myForm: FormGroup;
  valueChangesSubscription: Subscription;

  constructor(private formBuilder: FormBuilder) {}

  ngOnInit() {
    this.myForm = this.formBuilder.group({
      // 表单控件初始化
    });

    this.valueChangesSubscription = this.myForm.valueChanges.subscribe(() => {
      // 表单控件值变化时的回调函数
    });
  }

  ngOnDestroy() {
    if (this.valueChangesSubscription) {
      this.valueChangesSubscription.unsubscribe();
    }
  }
}