Display Context

displayContext

    public static class HtmlHelperExtension
    {
        public static string ActiveCss<T>(this HtmlHelper helper, T pageId, string activeClass = "active")
        {
            var displayContext = helper.ViewData.DisplayContext<T>();
            if (EqualityComparer<T>.Default.Equals(displayContext, pageId))
            {
                return activeClass;
            }
            return string.Empty;
        }
    }