从多个复选框获取字符串形式的值

Question

我知道这个问题已被多次问及回答，但似乎无法弄清楚如何将其实现到我的应用程序中。我对Ionic和Angular还是很陌生。

我有一个下拉复选框列表，用户可以在其中选择一个或多个答案。我需要选择要作为字符串发送的值。提交表单时，出现此错误。无论是一个还是多个答案，都会发生此错误。

    <ion-item>
      <ion-label stacked>1. Type of Incident or Observation</ion-label>
      <ion-select multiple="true" formControlName="firstQuestionAnswer" required [(ngModel)]="stopCardRequest.firstQuestionAnswer">
        <ion-option *ngFor="let firstQuestionAnswer of firstQuestionOptions" value="{{firstQuestionAnswer.value}}">{{firstQuestionAnswer.name}}</ion-option>
      </ion-select>
    </ion-item>

TS

  firstQuestionOptions = [
    { name: "Near Miss", value: "Near Miss" },
    { name: "First Aid", value: "First Aid" },
    { name: "Medical Beyond First Aid (HSE will conduct investigation)", value: "Medical Beyond First Aid (HSE will conduct investigation)" },
    { name: "Lost Time", value: "Lost Time" },
    { name: "Environmental (spills / releases)" ,value: "Environmental (spills / releases)" },
    { name: "Security", value: "Security" },
    { name: "Vehicle / Equipment Incident", value: "Vehicle / Equipment Incident" },
    { name: "Fire", value: "Fire"  },
    { name: "Illness", value: "Illness" },
    { name: "General Observation", value: "General Observation" }
  ];

  public submitRequest(values) {
    this.showLoading().then(() => {
      this.stopCardProvider.save(this.stopCardRequest).subscribe(
        () => {
          this.logger.info("Stop Card sent");
          this.alertProvider.showSubmission();
          this.stopCardForm.reset();
          // Dismiss loading overlay.
          this.loading.dismiss();
        },
        error => {
          // Dismiss loading overlay.
          this.loading.dismiss();
          this.alertProvider.showError(error);
        });
    });
  }

在模型中，firstQuestionAnswer是一个字符串。我不确定其他人还需要回答什么，所以请让我知道，我会尽力而为。