我们如何在角度2中设置单选按钮的默认值 [英] How can we set the default value of radio button in angular 2

问题描述

我有一个模型驱动的表单，想显示基于无线电输入的字段.代码:-

I have a Model driven form and want to show the fields based on radio input. Code :-

       <div class="form-group">
          <md-radio-group class="form-control"  id="radio1" formControlName="selection">
            <md-radio-button  [value]="A" >A</md-radio-button>
            <md-radio-button  [value]="B">B</md-radio-button>
          </md-radio-group>
        </div>

        <div class="form-group" *ngIf="selection.value=='A'">
          <md-input-container>
              <textarea md-input placeholder="A" class="form-control"
                        formControlName="A"
                        style="border:none;"></textarea>
          </md-input-container>
        </div>
        <div class="form-group" *ngIf="selection.value=='B'">
          <md-input-container>
            <input md-input placeholder="B" class="form-control"
                   formControlName="B"
                   style="border:none;">
          </md-input-container>            
        </div>

由于无法读取未定义的属性'值'"而出现错误由于未选择任何广播.

Getting error as "Cannot read property 'value' of undefined" As no radio is selected.

我如何指定选择第一个作为默认值.

How can I specify to select the first one as default.

推荐答案

您需要传递 string 作为收音机的值.现在，Angular试图找到名称为 A 的变量.

You need to pass a string as a value for the radio. Right now Angular tries to find a variable with the name A.

<md-radio-group class="form-control" [(ngModel)]="selection.value" 
                id="radio1" formControlName="selection">
  <md-radio-button [value]="'A'">A</md-radio-button>
  <md-radio-button [value]="'B'">B</md-radio-button>
</md-radio-group>

您在对相应组件中的 selection.value 分配值时初始化无线电:

You initialize the radio as you assign a value to selection.value in the according component:

class MyRadioComponent {
  selection = {"value":"A"};
}

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