如何在primeng下拉列表中更改自定义错误消息

errorMessage: string;

<p-dropdown [(ngModel)]="selectedItem" [ngModelOptions]="{standalone: true, errorMessage: errorMessage}">
  <!-- 下拉列表选项 -->
</p-dropdown>

updateErrorMessage() {
  if (this.selectedItem === null) {
    this.errorMessage = '请选择一个选项';
  } else {
    this.errorMessage = '';
  }
}

<p-dropdown [(ngModel)]="selectedItem" [ngModelOptions]="{standalone: true, errorMessage: errorMessage}" (ngModelChange)="updateErrorMessage()">
  <!-- 下拉列表选项 -->
</p-dropdown>