Angular 2设置选择的开始值 [英] Angular 2 Set begin value of select

问题描述

这是我的选择代码:

   <select class="form-control" [(ngModel)]="selectedPrototypeSelector" (ngModelChange)="onPrototypeChange()">
       <option *ngFor="#p of prototypes" [value]="p.selector">
             {{ p.selectorName }}
       </option>
   </select>

如何为该 select选项设置标准开始值?我以为我必须设置此变量:

How do I set a standard begin value to this select option I thought i have to set this variable:

 selectedPrototypeSelector: string;

为此: selectedPrototypeSelector:string ="Test";

但是"Test" 不在选择框中首先显示.begin值为空，我如何将其设置为:选择您的选项.

But the "Test" is not showing first in the select box The begin value is empty, how do I set this for example to: Select your option.

这里是 PLUNKER

如您所见，当我将值设置为 p.selector 时，选择框为空；对于第二个选择，当我给出 constraint 的值时，选择框也为空:

as you can see the select box is empty while i set the value p.selector and the same for the second select where i give the value of constraint:

 <select class="form-control" [(ngModel)]="expression.constraint">
     <option *ngFor="#constraint of prototype.constraints" [value]="constraint">
         {{ constraint }}
     </option>
 </select>

我想将每个选择框的开始值设置为静态 string ="Select a option";

I want to set the begin value of every select box to a static string = "Select an option";

推荐答案

与 ngValue

<select class="form-control" [(ngModel)]="selectedPrototypeSelector" (ngModelChange)="onPrototypeChange()">
   <option *ngFor="let p of prototypes" [ngValue]="p">
         {{ p.id }}
   </option>
</select>    

只需将 selectedPrototypeSelector 设置为您要选择的值即可.

Just set selectedPrototypeSelector to the value you want to have selected.

柱塞示例

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