在页面加载时将下拉选择选项设置为默认值

Question

下面是我的代码。我希望“选择文档类型”在最初加载表单时显示。因此，我将第一个设置为此，第二个是从后端获取日期。 Dropdownlist

<select class="custom-select" name="documentType" [(ngModel)]="myDocument.documentType.id"
                       #documentType="ngModel" [ngClass]="{'alert-border': documentType.errors?.emptyField}">
                 <option value="0" >Select the type of document</option>
                 <option [value]="documentType.id" *ngFor="let documentType of docTypes">{{documentType.denomination}}</option>
               </select>

我尝试过：

<option value="0" selected= "selected">Select the type of document</option>

没有运气。

Answer 1

您可以在TS文件中设置：

myDocument.documentType.id = "defaultValue"

Answer 2

尝试下面，

将ngModel属性更改为[（ngModel）] =“ selectedDocumentTypeId”

<select class="custom-select" name="documentType" [(ngModel)]="selectedDocumentTypeId"
   #documentType="ngModel" [ngClass]="{'alert-border': documentType.errors?.emptyField}">
     <option value="0" >Select the type of document</option>
     <option [value]="documentType.id" *ngFor="let documentType of docTypes">{{documentType.denomination}}</option>
</select>

在您的ts文件中

selectedDocumentTypeId: string = '';

ngOnInit() { 
  this.selectedDocumentTypeId  = docTypes[0].id; /* Hoping docTypes array exist before this statement*/
}

Answer 3

<option [ngValue]="0">Select the type of document</option>

*确保myDocument.documentType.id的初始值为0。