Export number type and string type of columns to excel

Hi

I use the following code for exporting data to excel,it works fine and fast,but there is a issue, that all columns exported as string type,I have string and number type data in datagrid,

how can I change this code for resolve that problem?

Thanks in Advance.

    public static void Export(this DataGrid dg)
    {
        ExportDataGrid(dg);
    }

    public static void ExportDataGrid(DataGrid dGrid)
    {
        
        SaveFileDialog objSFD = new SaveFileDialog() { DefaultExt = "xml", Filter = "Excel XML (*.xml)|*.xml", FilterIndex = 1 };
        if (objSFD.ShowDialog() == true)
        {
            string strFormat = objSFD.SafeFileName.Substring(objSFD.SafeFileName.IndexOf('.') + 1).ToUpper();
            StringBuilder strBuilder = new StringBuilder();
            if (dGrid.ItemsSource == null) return;
            List<string> lstFields = new List<string>();
            if (dGrid.HeadersVisibility == DataGridHeadersVisibility.Column || dGrid.HeadersVisibility == DataGridHeadersVisibility.All)
            {
                foreach (DataGridColumn dgcol in dGrid.Columns)
                lstFields.Add(FormatField(dgcol.Header.ToString(), strFormat));
                BuildStringOfRow(strBuilder, lstFields, strFormat);
            }
            foreach (object data in dGrid.ItemsSource)
            {
                lstFields.Clear();
                foreach (DataGridColumn col in dGrid.Columns)
                {
                    string strValue = "";                    
                    Binding objBinding = null;
                    if (col is DataGridBoundColumn)
                        objBinding = (col as DataGridBoundColumn).Binding;
                    if (col is DataGridTemplateColumn)
                    {
                        //This is a template column... let us see the underlying dependency object
                        DependencyObject objDO = (col as DataGridTemplateColumn).CellTemplate.LoadContent();
                        FrameworkElement oFE = (FrameworkElement)objDO;
                        FieldInfo oFI = oFE.GetType().GetField("TextProperty");
                        if (oFI != null)
                        {
                            if (oFI.GetValue(null) != null)
                            {
                                if (oFE.GetBindingExpression((DependencyProperty)oFI.GetValue(null)) != null)
                                    objBinding = oFE.GetBindingExpression((DependencyProperty)oFI.GetValue(null)).ParentBinding;
                            }
                        }
                    }
                    if (objBinding != null)
                    {
                        if (objBinding.Path.Path != "")
                        {
                            PropertyInfo pi = data.GetType().GetProperty(objBinding.Path.Path);
                            if (pi != null) strValue = pi.GetValue(data, null).ToString();
                        }
                        if (objBinding.Converter != null)
                        {
                            if (strValue != "")
                                strValue = objBinding.Converter.Convert(strValue, typeof(string), objBinding.ConverterParameter, objBinding.ConverterCulture).ToString();
                            else
                                strValue = objBinding.Converter.Convert(data, typeof(string), objBinding.ConverterParameter, objBinding.ConverterCulture).ToString();
                        }
                    }
                    lstFields.Add(FormatField(strValue,strFormat));
                }
                BuildStringOfRow(strBuilder, lstFields, strFormat);
            }
            StreamWriter sw = new StreamWriter(objSFD.OpenFile());
            if (strFormat == "XML")
            {
                //Let us write the headers for the Excel XML
                sw.WriteLine("<?xml version=\"1.0\" encoding=\"utf-8\"?>");
                sw.WriteLine("<?mso-application progid=\"Excel.Sheet\"?>");
                sw.WriteLine("<Workbook xmlns=\"urn:schemas-microsoft-com:office:spreadsheet\">");
                sw.WriteLine("<DocumentProperties xmlns=\"urn:schemas-microsoft-com:office:office\">");
                sw.WriteLine("<Author>Arasu Elango</Author>");
                sw.WriteLine("<Created>" +  DateTime.Now.ToLocalTime().ToLongDateString() + "</Created>");
                sw.WriteLine("<LastSaved>" + DateTime.Now.ToLocalTime().ToLongDateString() + "</LastSaved>");
                sw.WriteLine("<Company>Atom8 IT Solutions (P) Ltd.,</Company>");
                sw.WriteLine("<Version>12.00</Version>");
                sw.WriteLine("</DocumentProperties>");
                sw.WriteLine("<Worksheet ss:Name=\"Export\" xmlns:ss=\"urn:schemas-microsoft-com:office:spreadsheet\">");
                sw.WriteLine("<Table>");
            }
            sw.Write(strBuilder.ToString());
            if (strFormat == "XML")
            {
                sw.WriteLine("</Table>");
                sw.WriteLine("</Worksheet>");
                sw.WriteLine("</Workbook>");
            }
            sw.Close();
        }
    }
    private static void BuildStringOfRow(StringBuilder strBuilder, List<string> lstFields, string strFormat)
    {
        switch (strFormat)
        {
            case "XML":
                strBuilder.AppendLine("<Row>");
                strBuilder.AppendLine(String.Join("\r\n", lstFields.ToArray()));
                strBuilder.AppendLine("</Row>");
                break;
            case "CSV":
                strBuilder.AppendLine(String.Join(",", lstFields.ToArray()));
                break;
        }
    }
    private static string FormatField(string data, string format)
    {
        switch (format)
        {
            case "XML":
                return String.Format("<Cell><Data ss:Type=\"String\">{0}</Data></Cell>", data);
            case "CSV":
                return String.Format("\"{0}\"", data.Replace("\"", "\"\"\"").Replace("\n", "").Replace("\r", ""));
        }
        return data;
    }