角度8中的动态复选框

Question

我正在使用Angular 8中的动态复选框...我正在将复选框名称列表形成一种方法，该方法导致我将其设置为数组..并且我已经将该数组绑定为HTML ..但是当我提交ngform时，它返回null值。我在这里添加我的代码

additionalCoverArray: Array<AdditionalCovers> = [];
GetQueryAdditionalCovers() {
    this._getCheckboxvalueService.getCheckBoxValues("GetAdditionalCovers").then(result => {
      this.checkBoxes = result;
      this.additionalCoverArray = this.checkBoxes;
      console.log(this.additionalCoverArray);
    });
  }
in html
div class="additionalcovers-form">
    <form #additionalCoversForm="ngForm" class="col-md-12" (ngSubmit)="onSubmit(additionalCoversForm.value)">
      <div class="row" *ngIf="additionalCoverArray">
        <div class="col-md-6">
          <div class="row">
            <div class="col-md-6" *ngFor="let objCheckbox of additionalCoverArray; let i=index">
              <input type="checkbox"   [(ngModel)]="objCheckbox.isMandatory" id="{{objCheckbox.displayValue}}" name="{{objCheckbox.displayValue}}" value="{{objCheckbox.displayValue}}" (change)="toggleVisibility($event)">
              <label>{{ objCheckbox.displayValue }}</label>
            </div>
            <div class="col-md-6">
              <label>No Years</label>
              <select (change)="change($event)" [(ngModel)]="noYearsArray.noYears" name="noYears" [ngModelOptions]="{standalone: true}">
                <option *ngFor="let objNoYears of noYears" [value]="objNoYears.displayValue">{{objNoYears.displayValue}}</option>
              </select>
            </div>
          </div>
        </div>