asp.net-mvc – 自定义HtmlHelper扩展方法在View中不可用？

'CheckBoxList' is not a member of 'System.Web.Mvc.HtmlHelper(Of Attenda.Stargate.Web.UserRolesViewModel)'.

谁能告诉我哪里出错了？

助手模块：

Imports System.Runtime.CompilerServices

Public Module InputExtensions

  <Extension()> _
  Public Function CheckBoxList(ByVal htmlHelper As HtmlHelper,ByVal name As String,ByVal listInfo As List(Of ListItem)) As String
    Return htmlHelper.CheckBoxList(name,listInfo,DirectCast(Nothing,IDictionary(Of String,Object)))
  End Function

  <Extension()> _
  Public Function CheckBoxList(ByVal htmlHelper As HtmlHelper,ByVal listInfo As List(Of ListItem),ByVal htmlAttributes As Object) As String
    Return htmlHelper.CheckBoxList(name,DirectCast(New RouteValueDictionary(htmlAttributes),ByVal htmlAttributes As IDictionary(Of String,Object)) As String
    If String.IsNullOrEmpty(name) Then
      Throw New ArgumentException("The argument must have a value","name")
    End If
    If listInfo Is Nothing Then
      Throw New ArgumentNullException("listInfo")
    End If
    If listInfo.Count < 1 Then
      Throw New ArgumentException("The list must contain at least one value","listInfo")
    End If
    Dim sb As New StringBuilder()
    For Each info As ListItem In listInfo
      Dim builder As New TagBuilder("input")
      If info.Selected Then
        builder.MergeAttribute("checked","checked")
      End If
      builder.MergeAttributes(Of String,Object)(htmlAttributes)
      builder.MergeAttribute("type","checkbox")
      builder.MergeAttribute("value",info.Value)
      builder.MergeAttribute("name",name)
      builder.InnerHtml = info.Text
      sb.Append(builder.ToString(TagRenderMode.Normal))
      sb.Append("<br />")
    Next
    Return sb.ToString()
  End Function

End Module

查看来源：

<%@ Page Title="" Language="VB" MasterPageFile="~/Views/Shared/TwoColumn.Master" Inherits="System.Web.Mvc.ViewPage(Of Attenda.Stargate.Web.UserRolesViewModel)" %>

<asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
  Edit User Roles
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
  <h2>Edit Roles for
    <%=Html.Encode(Model.User.UserName)%></h2>
    <div>
    <%=Html.CheckBoxList("Roles",Model.Roles)%>
    </div>
</asp:Content>
<asp:Content ID="Content3" ContentPlaceHolderID="cphLeftPanel" runat="server">
</asp:Content>