如何使用静态项创建ASP.NET MVC HTML.DropDownList?

我想创建一个包含两个项目的下拉列表:零件名称和 NSN .

此DropDownList将用作搜索框控件的一部分,该控件将作为母版页的一部分进行部分呈现。用户将输入搜索文本并从下拉列表中选择零件名称或NSN,然后单击提交。查询将基于搜索文本返回结果。我已经定义了PartsController,它的相关部分如下:

    Function Search(ByVal searchtext As String, ByVal SearchType As String) As ActionResult
        Dim searchlist As List(Of String) = New List(Of String)
        searchlist.Add("Part Name")
        searchlist.Add("NSN")
        ViewData("searchlist") = New SelectList(searchlist)

        If SearchType = "PARTNAME" Then
            Dim SearchResult = From p In _entities.PartList _
              Where p.PARTNAME = searchtext _
              Select p
            Return View(SearchResult)
        End If
        If SearchType = "NSN" Then
            Dim SearchResult = From p In _entities.PartList _
              Where p.NSN = searchtext _
              Select p
            Return View(SearchResult)
        End If
        Return View("UnknownType")
    End Function

partsform.ascx定义如下:

    <%@ Control Language="VB" Inherits="System.Web.Mvc.ViewUserControl(Of DielToolMVC.PartList)" %>
    <%=Html.ValidationSummary("Please correct the errors and try again")%>
    <%  Using (Html.BeginForm("Search", "PartsController"))%>
        <fieldset>
            <p>
                <label for="Parts">Please enter a part description or NSN.</label>
                <%=Html.TextBox("searchtext") %>
                <%=Html.DropDownList("searchlist")%>
                <%=Html.ValidationMessage("Part Name or NSN", "*")%>
            </p>
            <p>
                <input type="submit" value="Search" />
            </p>
        </fieldset>
    <% End Using%>

调试时,我收到以下错误消息:

没有键为“searchlist”且类型为“ienumerable”的ViewData项。

我有点困惑 MSDN 文档演示了类似的示例。然而,在下面这些例子之后,我得到了这个错误。我忽略了什么?