這應該是剛開始學ASP.NET MVC 常犯的錯誤，一般我們會新增一個資料夾”Helpers”來放 HtmlHelper的程式，如在資料夾新增一個class，如:HMTLHelperExtensions.cs。
using System;
using System.Web.Mvc;
namespace DemoCustomIndentity.Helpers
{
public static class HMTLHelperExtensions
{
public static string IsSelected(this HtmlHelper html, string controller = null, string action = null, string cssClass = null)
{
if (String.IsNullOrEmpty(cssClass))
cssClass = "active";
string currentAction = (string)html.ViewContext.RouteData.Values["action"];
string currentController = (string)html.ViewContext.RouteData.Values["controller"];
if (String.IsNullOrEmpty(controller))
controller = currentController;
if (String.IsNullOrEmpty(action))
action = currentAction;
return controller == currentController && action == currentAction ?
cssClass : String.Empty;
}
public static string PageClass(this HtmlHelper html)
{
string currentAction = (string)html.ViewContext.RouteData.Values["action"];
return currentAction;
}
}
}