验证不适用于具有多个控件的formArray

Question

我正在研究mat-chip-list，其中声明了要输入的formArray控件。

当前行为： 当我只提交表单而没有填写任何表单字段时，mat-chip-list里面没有任何formcontrols，但是当我打印formGroup时，required：true验证显示，但是mat-chio-list框的红色边框没有显示显示。

预期行为： 表单验证必须显示带有红色边框的mat-chip-list

我的Component.ts：

this.composeMailForm = new FormGroup({
  to_emails: new FormArray([], Validators.required),
  cc_emails: new FormControl(),
  bcc_emails: new FormControl(),
  from_email: new FormControl(),
  subject: new FormControl('', Validators.required),
  body: new FormControl('', Validators.required),
});

onSubmit(){
  console.log("form controls after submit",this.composeMailForm);
  if(this.composeMailForm.valid){
   ------------
   ------------
  }else{
    this.composeMailForm.controls.body.markAsTouched();
    const ctrls = this.composeMailForm.get('to_emails') as FormArray;
    ctrls.markAsTouched();
    ctrls.controls.forEach(control => control.markAsTouched());
    this.composeMailForm.controls.subject.markAsTouched();
  }

add(event: MatChipInputEvent, email_type): void {
  const input = event.input;
  const value = event.value;
  if ((value || '').trim()) {
    if(email_type === 'to_email'){
      const to_emails = this.composeMailForm.get('to_emails') as FormArray;
      to_emails.push(this.fb.control(value.trim()));
    }
  }
}

remove(index: number, email_type): void {
  if(email_type === 'to_email'){
    const to_emails = this.composeMailForm.get('to_emails') as FormArray;
    if (index >= 0) {
      to_emails.removeAt(index);
    }
  }
}

HTML：

<mat-label>To</mat-label>
<mat-chip-list #chipList ngDefaultControl formArrayName="to_emails" >
  <mat-chip *ngFor="let email of composeMailForm.get('to_emails').controls; let i = index;" [selectable]="selectable" [removable]="removable"
                      (removed)="remove(i,'to_email')" ngDefaultControl >
 {{email.value}}
   <mat-icon matChipRemove *ngIf="removable">cancel</mat-icon>
  </mat-chip>
  <input [matChipInputFor]="chipList" [matChipInputSeparatorKeyCodes]="separatorKeysCodes"
                      [matChipInputAddOnBlur]="addOnBlur" (matChipInputTokenEnd)="add($event,'to_email')" >
</mat-chip-list>

如何实现这一目标，任何想法？谢谢。