AngularJs ng-class活动不起作用

Question

HTML代码：在 li 标记

中无效的活跃课程

<ul class="list-group">
            <li class="list-group-item" ng-class="{'active': isSelectedBookmark(bookmark.id)}" ng-repeat="bookmark in bookmarks | filter:{category:currentCategory.name}">
                <button ng-click="setEditedBookmark(bookmark); startEditing();" type="button" class="btn btn-link">
                    <span class="glyphicon glyphicon-pencil"></span>
                </button>
                <a href="{{bookmark.url}}" target="_blank">{{bookmark.title}}</a>
            </li>
        </ul>

javascript文件：

$scope.bookmarks = [
    {'id':0, 'title':"AngularJs", 'url':"http://angularjs.org", 'category':"Development"},
    {'id':1, 'title':"Egghead.io", 'url':"http://angularjs.org", 'category':"Development"},
    {'id':2, 'title':"HTML", 'url':"http://w3schools.com", 'category':"Design"},
    {'id':3, 'title':"CSS", 'url':"http://w3schools.com", 'category':"Design"},
    {'id':4, 'title':"JavaScript", 'url':"http://w3schools.com", 'category':"Development"}
];
$scope.editedBookmark = null;
function setEditedBookmark(bookmark) {
    $scope.editedBookmark = angular.copy(bookmark);
}
function isSelectedBookmark(bookmarkId) {
    return $scope.editedBookmark !== null && $scope.editedBookmark.id === bookmarkId;
}
$scope.setEditedBookmark = setEditedBookmark;
$scope.isSelectedBookmark=isSelectedBookmark;

如何让活动类在这种情况下工作？