จะเพิ่ม parent node ลงในไฟล์ xml ที่มีอยู่แล้วทำได้ไหมครับ

        public static void Write(string xmlPath, string tagName, DataTable dtData)
        {
            if (File.Exists(xmlPath))
            {
                File.Delete(xmlPath);
            }

            XmlTextWriter writer = new System.Xml.XmlTextWriter(xmlPath, System.Text.Encoding.UTF8);
            writer.WriteStartDocument();
            writer.WriteStartElement("dataroot");
            writer.WriteAttributeString("xmlns", "od", null, "urn:schemas-microsoft-com:officedata");
            writer.WriteAttributeString("generated", DateTime.Now.ToString("yyyy-MM-ddTHH:mm:ss"));

            writer.Indentation = 0;
            writer.Formatting = Formatting.Indented;

            foreach (DataRow dr in dtData.Rows)
            {
                writer.WriteStartElement(tagName);

                foreach (DataColumn dc in dtData.Columns)
                {
                    if (dc.DataType == typeof(DateTime))
                    {
                        writer.WriteElementString(dc.ColumnName, (dr[dc.ColumnName] != DBNull.Value) ? dr.Field<DateTime>(dc.ColumnName).ToShortDateString() : string.Empty);
                    }
                    else
                    {
                        writer.WriteElementString(dc.ColumnName, (dr[dc.ColumnName] != null) ? dr[dc.ColumnName].ToString() : string.Empty);
                    }
                }

                writer.WriteEndElement();
            }

            writer.WriteEndElement();
            writer.WriteEndDocument();

            if (writer != null)
            {
                writer.Flush();
            }

            if (writer.WriteState != WriteState.Closed)
            {
                writer.Close();
            }
        }

Public Class my_GridView_Generic
    Inherits GridView
...
...
    Protected Overrides Sub OnSorting(e As System.Web.UI.WebControls.GridViewSortEventArgs)
        If Not e.SortExpression.Equals(String.Empty) Then
            ViewState("SortDirection") = If(ViewState("SortDirection") = Nothing OrElse
                                            ViewState("SortDirection").Equals("") OrElse
                                            ViewState("SortDirection") = "0", "1", "0")
            Me._DataModel = SortColumnByLamda(e.SortExpression, ViewState("SortDirection"))
            Me.DataSource = Me._DataModel 'DirectCast(Me._DataModel, List(Of Any type))
            Me.DataBind()
            Me.HeaderRow.Cells(Me.GetColumnIndex(e.SortExpression)).CssClass = If(ViewState("SortDirection") = "0",
                                                                                  "sortasc-header", "sortdesc-header")
            'MyBase.OnSorting(e)
        End If
    End Sub

    Private Function SortColumnByLamda(ByVal colName As String, ByVal sortDirection As String) As Object
        Dim lstDyn = Enumerable.Cast(Of Object)(Me._DataModel)
        If sortDirection = "1" Then 'Descending
            lstDyn = lstDyn.OrderByDescending(Function(c) c.GetType().InvokeMember(colName, BindingFlags.GetProperty, Nothing, c, Nothing)).ToList()
        Else
            lstDyn = lstDyn.OrderBy(Function(c) c.GetType().InvokeMember(colName, BindingFlags.GetProperty, Nothing, c, Nothing)).ToList()
        End If
        Return lstDyn
    End Function

End Class