asp.net – DropDownList SelectedIndex值未在AutoPostback上更

第一个下拉列表填充：

Dim db As New linqclassesDataContext
Dim categories = (From c In db.faq_cats)

NewFaqDropDownCategory.DataSource = categories
NewFaqDropDownCategory.DataTextField = "category"
NewFaqDropDownCategory.DataValueField = "category_id"
NewFaqDropDownCategory.DataBind()
Unset(categories)
Unset(db)

填充第二个下拉列表：

Protected Sub NewFaqDropDownCategory_SelectedIndexChanged(ByVal sender As Object,ByVal e As System.EventArgs)
    Dim temp As Integer = CInt(Val(NewFaqDropDownCategory.SelectedIndex))
    MsgBox(theDrop.SelectedValue)
    Return

    'Dim db As New linqclassesDataContext
    'Dim faqs = (From f In db.faqs Where f.category = NewFaqDropDownCategory.SelectedValue)

    'NewFaqDropDownList.DataSource = faqs
    'NewFaqDropDownList.DataTextField = "question"
    'NewFaqDropDownList.DataValueField = "id"
    'NewFaqDropDownList.DataBind()
    'NewFaqLabel.Visible = True
    'NewFaqDropDownList.Visible = True
    'Unset(faqs)
    'Unset(db)
End Sub

第一个下拉列表的加价……

<asp:DropDownList ID="NewFaqDropDownCategory" AutoPostBack="true" runat="server" OnSelectedIndexChanged="NewFaqDropDownCategory_SelectedIndexChanged">
</asp:DropDownList>

第二个……

<asp:DropDownList ID="NewFaqDropDownList" runat="server" Visible="false">
</asp:DropDownList>

无论我尝试过什么,我总是得到“1”(第二个下拉列表中第一个项目的值).我之前提到的帖子说这与AutoPostBack有关,而服务器不知道列表是否已更新.

任何人都可以为我澄清这一点吗？