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

Question

我翻译了 Jeremiah Clark 的 CheckBoxList Helper for MVC进入我的 VB.Net 项目，但是当我尝试在我的 View 中使用该方法时出现错误

'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？

辅助模块:

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 name As String, ByVal listInfo As List(Of ListItem), ByVal htmlAttributes As Object) As String
    Return htmlHelper.CheckBoxList(name, listInfo, DirectCast(New RouteValueDictionary(htmlAttributes), IDictionary(Of String, Object)))
  End Function

  <Extension()> _
  Public Function CheckBoxList(ByVal htmlHelper As HtmlHelper, ByVal name As String, ByVal listInfo As List(Of ListItem), 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

查看源代码:

<%@ 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>

Answer 1

您需要将包含自定义帮助程序类的命名空间导入您的 View 页面。您可以在页面本身或在所有页面的 web.config 文件中执行此操作。首先将代码放入命名空间。

<%@ Import Namespace="MyProject.Extensions" %>

或(在 web.config 中)

<pages>
   ...
   <namespaces>
       ...
       <add namespace="MyProject.Extensions" />
   </namespaces>
</pages>