我有一个指令，template里面的ng-class="{glyphicon-chevron-down:isOpened, glyphicon-chevron-right: !isOpened}", 给glyphicon-chevron-down和glyphicon-chevron-right加单引号和双引号都会报错，不加引号也会报错(ng-class里面的classname如果有 - 的话要加引号的)。这种情况该怎么办呢？

.directive('brandItem', function (){
    return {
        restrict: 'EA',
        require: '^brandList',
        transclude: true,
        replace: true,
        scope: {
            title: '='
        },
        template: '<li ng-click="toggle()" class="list-group-item">'
                    +'<label><span class="glyphicon" ng-class="{glyphicon-chevron-down:isOpened, glyphicon-chevron-right: !isOpened}"></span>&nbsp;{{name}}</label>'
                    +'<p ng-transclude></p>'
                +'</li>',
        link: function (scope, element, attrs, brandListCtrl){
            scope.isOpened = false;
            brandListCtrl.addItem(scope);
            scope.toggle = function (){
                this.isOpened = !this.isOpened;
                brandListCtrl.getOpened(scope);
            }
        }
    }
});