如何在angular中展平嵌套的formGroups

import { Directive, Input, OnInit } from '@angular/core';
import { FormGroup } from '@angular/forms';

@Directive({
  selector: '[flattenFormGroup]'
})
export class FlattenFormGroupDirective implements OnInit {
  @Input('flattenFormGroup') formGroup: FormGroup;

  constructor() { }

  ngOnInit() {
    this.flattenFormGroup(this.formGroup);
  }

  private flattenFormGroup(formGroup: FormGroup) {
    Object.keys(formGroup.controls).forEach(key => {
      const control = formGroup.get(key);
      if (control instanceof FormGroup) {
        this.flattenFormGroup(control);
        Object.keys(control.controls).forEach(innerKey => {
          const innerControl = control.get(innerKey);
          formGroup.addControl(innerKey, innerControl);
        });
        formGroup.removeControl(key);
      }
    });
  }
}

<form [formGroup]="myFormGroup" flattenFormGroup>
  <!-- 表单控件 -->
</form>