单击按钮值时不以角度js更新

This html code :

这个HTML代码：

<md-button class="md-primary " ng-click="setDevice('phone')">Phone           
        </md-button>
<md-button class="md-primary " ng-click="setDevice('tablet')">
           Tablet
        </md-button>

<div class="area-{{setDevice}}">
    <me-iphone tmp-url="{{appTemplateUrl}}"></me-iphone>
</div>
<md-button clas