ASP.NET DataTable output problem

I can't for the life of me work out what I am doing wrong here, despite much searching on SO/Google.

Basically I have a simple DataTable which is held in ViewState and adjusted during postbacks. When I try to write out the values, it is just an empty string. Please find below an abbreviated example of what I have - the output in this case just winds up as a string of apostrophes (one for each execution) so it looks as though the rows are being added, but the ("Product") column is empty.

Thanks for your help.

    Dim dtItems As New DataTable
    If ViewState("Items") Is Nothing Then
        Dim dcColumn As DataColumn
        dcColumn = New DataColumn()
        dcColumn.DataType = Type.GetType("System.String")
        dcColumn.ColumnName = "Product"
        dtItems.Columns.Add(dcColumn)
        ViewState("Items") = dtItems
    End If
    dtItems = CType(开发者_运维问答ViewState("Items"), DataTable)
    Dim drRow As DataRow
    drRow = dtItems.NewRow()
    drRow("Product") = "The Product"
    dtItems.Rows.Add()
    For Each drRow In dtItems.Rows
        txtTestDT.Text += drRow(("Product")).ToString & "!"
    Next

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try replacing:

dtItems.Rows.Add()

with

dtItems.Rows.Add(drRow)