ng-model如何绑定二选一的单选项框？

Question

Answer 1

<label>
    <input type="radio" ng-model="sex" value="male">
    <span>男</span>
</label>
<label>
    <input type="radio" ng-model="sex" value="female">
    <span>女</span>
</label>
{{sex}}

至于name属性，我试了一下只要ng-model绑定的值一样就认为是一组

Answer 2

用ng-checked来

<label class="">
    <input type="radio" ng-checked="option==1" ng-click="option=1">
    <span>a</span>
</label>
<label class="">
    <input type="radio" ng-checked="option==2" ng-click="option=2">
    <span>b</span>
</label>

Answer 3

单选框少了name属性，浏览器怎么知道你是一组单选框，angular怎么知道是一组单选框？