以下是按键创建动态表单控件的步骤/概念：
1.为answer控件创建一个FormGroup。
1.迭代rating数组并将FormControl（以question为键）添加到answerFormGroup。
1.使用*ngFor和keyvalue管道生成answerFormGroup的嵌套窗体控件。

ngOnInit() {
  this.form = this.fb.group({
    answer: this.fb.group({}),
    comments: this.fb.control(''),
  });

  for (let rate of this.rate.rating) {
    this.answer.addControl(rate.question.toString(), new FormControl());
  }
}

get answer(): FormGroup {
  return this.form.controls.answer as FormGroup;
}

answerControl(formControl: AbstractControl<any, any>): FormControl {
  return formControl as FormControl;
}

<div formGroupName="answer">
  <ng-container *ngFor="let control of answer.controls | keyvalue">
    <label>Question {{ control.key }}</label>
    <rating [max]="5" [formControl]="answerControl(control.value)"></rating>
    <br />
  </ng-container>
</div>

Demo @ StackBlitz