给li标签添加ng-repeat='x in provinceArr' 后，鼠标移入移出不

Question

给li标签添加ng-repeat指令后，ng-mouseenter="show = true" ng-mouseleave="show = false"居然不起作用，为什么啦？求解？代码如下：
<ul class="im-dropdown-ul">

    <li ng-repeat='x in provinceArr' ng-mouseenter="show = true" ng-mouseleave="show = false">
    <span><input type="checkbox"><span>{{x}}</span></span></li></ul><div ng-show="show">Hello!</div>