我试图使用以下代码：

public static class LinkExtensions
{
    public static MvcHtmlString MyActionLink(
        this HtmlHelper htmlHelper,string linkText,string action,string controller)
    {
        var currentAction = htmlHelper.ViewContext.RouteData.GetrequiredString("action");
        var currentController = mlHelper.ViewContext.RouteData.GetrequiredString("controller");

        if (action == currentAction && controller == currentController)
        {
          var anchor = new TagBuilder("a");
          anchor.Attributes["href"] = "#";
          anchor.AddCssClass("currentPageCSS");
          anchor.SetInnerText(linkText);
          return MvcHtmlString.Create(anchor.ToString());
         }

         return htmlHelper.ActionLink(linkText,action,controller);
    }
}

从Custom ActionLink helper that knows what page you’re on

但我得到了

System.Web.Mvc.HtmlHelper’ does not contain a definition for
‘ActionLink’ and no extension method ‘ActionLink’ accepting a first
argument of type ‘System.Web.Mvc.HtmlHelper’ could be found (are you
missing a using directive or an assembly reference?