Angular 8动态复选框和来自api的数据的下拉列表

Question

这是我的堆叠闪电战https://stackblitz.com/edit/angular-w8g8ng?file=src%2Fapp%2Fapp.component.html

如果分区为空，我想隐藏下拉列表，并且还将下拉列表的值默认为第一个。我怎样才能做到这一点？请帮助。

<form [formGroup]='newEmployeeForm' class="w-60-l">
  <label [for]="i"  formArrayName="planDivList"
          *ngFor="let plan of newEmployeeForm.controls.planDivList.controls; let i = index"><br>

          <input [name]="i" [id]="i"  type="checkbox" [formControlName]="i">
          {{planDivList[i].planCode}}

          <label for="inputDiv">Divisions
            <select id="inputDiv" [(ngModel)]="division" (ngModelChange)="errMsg = ''"
              [ngModelOptions]="{standalone: true}" formcontrolName='divCtrl'>
              <option *ngFor="let division of planDivList[i].divisions">{{division.divisionName}}</option>
            </select>
          </label>

        </label>

        <div
          *ngIf="formInvalid && newEmployeeForm.controls.planDivList.hasError('required')">
        At least one plan must be selected
        </div>
</form>

这是我来自api的数据集，它在不断变化

 planDivList = [
    { planCode: "B3692", divisions: [] },
    { planCode: "B3693", divisions: [] },
    { planCode: "B67", divisions: [{ divisionCode: "2", divisionName: "Assisted Living " }, { divisionCode: "1", divisionName: "LILC" }] },
    { planCode: "B69", divisions: [{ divisionCode: "3", divisionName: "Four Seasons" }, { divisionCode: "2", divisionName: "Lakeside" }, { divisionCode: "1", divisionName: "Sunrise" }] }

  ];    

Answer 1

要隐藏下拉菜单，您需要在select标记中添加* ngIf，如下所示：

<select *ngIf="planDivList[i].divisions.length > 0" id="inputDiv"...

并且要选择下拉列表的第一个值，请在创建时设置formControl的值，例如：

divCtrl: new FormControl(this.planDivList[0].divisions[0], [Validators.required])