how to import gridview data to excel in asp.net?

DataTable DataTabledt = new DataTable("Employee");
       Microsoft.Office.Interop.Excel.Application excel = null;
       Microsoft.Office.Interop.Excel.Workbook workbook1 = null;
       object missing = Type.Missing;
       Microsoft.Office.Interop.Excel.Worksheet worksheet1 = null;
       Microsoft.Office.Interop.Excel.Range range = null;
private void cmdExport_Click(object sender, RoutedEventArgs e)
     {
         string p = "C:\\Documents and Settings\\divyar\\My Documents\\Visual Studio 2010\\Projects\\prjCTM\\WpfApplication1\\Excel\\ex.xlsx";
             //System.Reflection.Assembly.GetExecutingAssembly().Location;
             //System.IO.Directory.GetCurrentDirectory();
         try
         {
             excel = new Microsoft.Office.Interop.Excel.Application();
             workbook1 = excel.Workbooks.Add();
             worksheet1 = (Microsoft.Office.Interop.Excel.Worksheet)workbook1.ActiveSheet;
             for (int index = 0; index < DataTabledt.Columns.Count; index++)
             {
                 worksheet1.Range["A1"].Offset[0, index].Value = DataTabledt.Columns[index].ColumnName;
             }
             for (int index = 0; index < DataTabledt.Rows.Count; index++)
             {
                 worksheet1.Range["A2"].Offset[index].Resize[1, DataTabledt.Columns.Count].Value = DataTabledt.Rows[index].ItemArray;
             }
             workbook1.Activate();
             workbook1.SaveAs(p);
             excel.Quit();
             MessageBox.Show(p);
         }
         catch (Exception ex)
         {
             MessageBox.Show("Error" + ex.ToString());
         }


     }