将项目插入下拉菜单时出现问题

Question

Seems to be a trivial problem, but can't pinpoint a solution.

I have a drop down bound to a datatable. I'm trying to insert a new item at position 0, but when the control is loaded, I don't see the new listitem or any errors.

Public Sub Page_Load(ByVal sender As Object, ByVal e As eventargs) Handles Me.Load
    If Not Page.IsPostBack Then
        loadRegistrantAbstracts()
    End If
End Sub
Public Sub loadRegistrantAbstracts()
    Dim obj As New Lookups
    Dim dtAbstracts As DataTable

    dtAbstracts = obj.getAbstracts()

    If dtAbstracts.Rows.Count > 0 Then
        With ddlAbstracts
            .DataSource = dtAbstracts
            .DataTextField = "DisplayName"
            .DataValueField = "AbstractID"
            .DataBind()
            .Items.Insert(0, New ListItem("Select Abstract..", "0"))
        End With
    End If
End Sub

Answer 1

Since the DropDownList is bound, it will render the "stuff" in the DataTable. You'll want to add the option for "Select Abstract ..." as a DataRow in the DataTable. When you change the source of the .DataSource, it will reflect in the DropDownList.

Most likely you are loading this from a database, so you may decide to include the "Select ..." option in the query:

SELECT 0 AS id, 'Select Abstract ...' AS abstract_name, 0 AS sort_order
UNION
SELECT dbo.abstracts.id, dbo.abstracts.name AS abstract_name, 1 as sort_order FROM dbo.abstracts
ORDER BY sort_order, abstract_name

Answer 2

The answer, thanks in part to HardCode, was the following:

Public Sub Page_Load(ByVal sender As Object, ByVal e As eventargs) Handles Me.Load
    If Not Page.IsPostBack Then
        loadRegistrantAbstracts()
    End If
End Sub
Public Sub loadRegistrantAbstracts()
    Dim obj As New Lookups
    Dim dtAbstracts As DataTable

    dtAbstracts = obj.getAbstracts()

    Dim row As DataRow = dtAbstracts.NewRow

    row("DisplayName") = "Select Abstract..."
    row("AbstractID") = "0"

    dtAbstracts.Rows.InsertAt(row, 0)

    If dtAbstracts.Rows.Count > 0 Then
        With ddlAbstracts
            .DataSource = dtAbstracts
            .DataTextField = "DisplayName"
            .DataValueField = "AbstractID"
            .DataBind()
        End With
    End If
End Sub