Underlining Headers from WPF Datagrid when printing using Excel print function

Question

Currently using the Excel print function to Export data from a WPF Datagrid and print it. Below is the code I am using:

 private void OnDataGridPrinting(object sender, RoutedEventArgs e)
    {
        System.Windows.Controls.PrintDialog Printdlg = new System.Windows.Controls.PrintDialog();
        if ((bool)Printdlg.ShowDialog().GetValueOrDefault())
        {
            // creating Excel Application  
            Microsoft.Office.Interop.Excel._Application app = new Microsoft.Office.Interop.Excel.Application();
            // creating new WorkBook within Excel application  
            Microsoft.Office.Interop.Excel._Workbook workbook = app.Workbooks.Add(Type.Missing);
            // creating new Excelsheet in workbook  
            Microsoft.Office.Interop.Excel._Worksheet worksheet = null;
            // see the excel sheet behind the program  
            app.Visible = false;
            // get the reference of first sheet. By default its name is Sheet1.  
            // store its reference to worksheet  
            worksheet = workbook.Sheets["Sheet1"];
            worksheet = workbook.ActiveSheet;
            // changing the name of active sheet  
            worksheet.Name = SelectedCustomer.CustName;
            // storing header part in Excel  

            CollectionViewSource itemCollectionViewSources;
            itemCollectionViewSources = (CollectionViewSource)(FindResource("ItemCollectionViewSources"));



            for (int i = 1; i < dgEndOfYear.Columns.Count + 1; i++)
            {
                **worksheet.Cells[1, i] = dgEndOfYear.Columns[i - 1].Header;**

            }
            // storing Each row and column value to excel sheet  
            for (int i = 0; i < CustomerEOYTotals.Count - 0; i++)
            {
                absvwEndOfYearTotal1 line = CustomerEOYTotals[i];
                worksheet.PageSetup.CenterHeader = "&UEnd Of Year Report " + CurrentYear;
                worksheet.Cells[i + 2, 1] = line.CalendarYear;
                worksheet.Cells[i + 2, 2] = line.CustName;
                worksheet.Cells[i + 2, 3] = line.MonthName;
                worksheet.Cells[i + 2, 4] = line.SumGal.Value.ToString();
                worksheet.Cells[i + 2, 5] = line.Manifest;
               
                worksheet.Columns.Cells.Font.FontStyle = Microsoft.Office.Interop.Excel.XlUnderlineStyle.xlUnderlineStyleSingle;
                worksheet.Cells.Style.HorizontalAlignment = Microsoft.Office.Interop.Excel.XlHAlign.xlHAlignCenter;
                worksheet.Columns.ColumnWidth = 14;

            }
           

            // Print the workbook
            workbook.PrintOut();

The line "worksheet.Cells[1, i] = dgEndOfYear.Columns[i - 1].Header" are the headers from the data grid I have made several attempts to style the headers so they are underlined like the below example when printed out but have had no luck any help would be appreciated: 

Answer 1

Try this:

worksheet.Cells[1, i] = dgCountyEOY.Columns[i - 1].Header;
                worksheet.Cells[1, i].Characters.Font.Underline = true;