html - 如何在选择下拉列表中应用占位符以及 Angular 6 中的 [ngmodel]？

Question

每当我使用 [(ngModel)] 时，第一个值变为空。但是当我删除 [(ngModel)] 时它工作正常。

 <select class="custom-select" id="campaignDropdown" [(ngModel)]="campaignInfo" placeholder="Select Campaign" (change)="hitApiFunction(campaignInfo)">
            <option value="" disabled selected>Select Campaign</option>
              <option *ngFor="let campData of campaigns" [ngValue]="campData"> 
                  {{campData.campaign_name}}
              </option>
            </select>

Answer 1

作者:@Krishna Rathore

可以使用[value]=""selected hidden

我已经在 Stackblitz 上创建了一个演示

<form role="form" class="form form-horizontal" (ngSubmit)="onSubmit()" #form="ngForm" ngNativeValidate>
    <div class="form-group row">
        <div class="col-xl-4 col-lg-6 col-md-12">
            <fieldset class="form-group">
                <label for="customSelect">Categories:</label>
                <select class="custom-select d-block w-100" id="Category" [(ngModel)]="Category" name="Category" required placeholder="d.ff">
                    <option hidden [value]=""  selected>Select one category </option>
                    <option *ngFor="let item of myBusinessList" [value]="item.id">{{item.name}}</option>
                </select>
            </fieldset>
        </div>
    </div>
    <button type="submit" class="btn btn-raised btn-danger">Save</button>
</form>