Angular 8：为选择标签设置默认选择值

Question

我想为 select 标签设置一个默认选项值，这些值在我的组件中声明为表格并使用 ngFor 指令显示：

<form>
    <div class="form-group col-4">
      <span class="badge badge-theme mb-3">Quantité</span>
      <select class="form-control" id="exampleFormControlSelect1">
        <option *ngFor="let quantity of Quantities" [ngValue]="quantity">{{quantity}}</option>
      </select>
    </div>
    <div class="form-group col-4">
      <span class="badge badge-theme mb-3">Message personnalisé</span>
      <textarea class="form-control" id="exampleFormControlTextarea1" rows="3"></textarea>
    </div>
  </form>

组件.ts

  Quantities = Array(50).fill(0).map((x,i)=>i);

Answer 1

您可以通过以下方式执行此操作：

组件.html

 <select [(ngModel)]="seletedValue" class="form-control" id="exampleFormControlSelect1">
        <option *ngFor="let quantity of Quantities" [ngValue]="quantity">{{quantity}}</option>
 </select>

组件.ts

seletedValue = ''; // set some default value from Quantities

或者

component.html

 <select [(ngModel)]="seletedValue" class="form-control" id="exampleFormControlSelect1">
        <option value="" [disabled]="true">Select quantity</option>
        <option *ngFor="let quantity of Quantities" [ngValue]="quantity">{{quantity}}</option>
 </select>