ถามเลื่อง export excel หน่อยครับ ผมตอ้งกาน format colum date นะครับ ต้องทำไง

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Excel = Microsoft.Office.Interop.Excel;
using System.Data;
using System.IO;

namespace MsExcel
{
    class InteropExcel : IDisposable
    {
        private object missing = Type.Missing;
        private object readOnly = true;

        private Excel.Application xlApp;
        private Excel.Workbook xlBook;
        private Excel.Range xlRange;

        private string filePath;
        private string message;
        private int sheetCount;
        private int rowCount;

        public InteropExcel(string FilePath)
        {
            filePath = FilePath;
            message = "Hello World!!!";
            sheetCount = 0;
            rowCount = 0;

            xlApp = new Excel.Application();
            xlApp.Visible = false;
            xlApp.ScreenUpdating = false;
            xlApp.DisplayAlerts = false;
        }

        public bool Export(DataSet DsData)
        {
            if(!Create())
                return false;

            foreach (DataTable DtData in DsData.Tables)
            {
                Excel.Worksheet xlSheet = (Excel.Worksheet)xlBook.Worksheets.Add(missing, missing, missing, missing);

                if(!FillData(xlSheet, DtData))
                    return false;

                sheetCount++;
            }

            if(!Save())
                return false;

            message = string.Format("Export '{0}' Success. ({1} Sheets, {2} Rows)", Path.GetFileName(filePath), sheetCount.ToString("#,##0"), rowCount.ToString("#,##0"));

            return true;
        }

        public bool Export(DataTable DtData)
        {
            if (!Create())
                return false;

            Excel.Worksheet xlSheet = (Excel.Worksheet)xlBook.Worksheets.Add(missing, missing, missing, missing);

            if (!FillData(xlSheet, DtData))
                return false;

            sheetCount++;

            if (!Save())
                return false;

            message = string.Format("Export '{0}' Success. ({1} Sheets, {2} Rows)", Path.GetFileName(filePath), sheetCount.ToString("#,##0"), rowCount.ToString("#,##0"));

            return true;
        }

        public bool Export(DataSet DsData, string TableName)
        {
            return Export(DsData.Tables[TableName]);
        }

        public bool Export(DataSet DsData, int TableIndex)
        {
            return Export(DsData.Tables[TableIndex]);
        }

        protected bool Create()
        {
            bool result = false;

            if (!File.Exists(filePath))
                File.Delete(filePath);

            try
            {
                xlBook = xlApp.Workbooks.Add(Microsoft.Office.Interop.Excel.XlWBATemplate.xlWBATWorksheet);
                result = true;
            }
            catch (System.Runtime.InteropServices.COMException ex)
            {
                message = ex.Message;
                Dispose();
            }

            return result;
        }

        protected bool Save()
        {
            bool result = false;

            try
            {
                xlBook.SaveAs(filePath, missing, missing, missing, missing, missing, Microsoft.Office.Interop.Excel.XlSaveAsAccessMode.xlNoChange, missing, missing, missing, missing, missing);
                result = true;
            }
            catch (System.Runtime.InteropServices.COMException ex)
            {
                message = ex.Message;
                Dispose();          
            }

            return result;       
        }

        protected bool FillData(Excel.Worksheet xlSheet, DataTable DtData)
        {
            int row = 2;
            int col = 1;

            xlSheet.Name = DtData.TableName;

            foreach (DataColumn Dc in DtData.Columns)
            {
                xlSheet.Cells[1, col] = string.Format("'{0}", Dc.ColumnName);
                xlRange = (Excel.Range)xlSheet.Cells[1, col];
                xlRange.Font.Name = "MS Sans Serif";
                xlRange.Font.Size = 10;
                xlRange.Interior.Color = System.Drawing.Color.LightYellow;
                xlRange.Borders.Color = System.Drawing.Color.LightGray;

                col++;
            }

            foreach (DataRow Dr in DtData.Rows)
            {
                col = 1;

                foreach (DataColumn Dc in DtData.Columns)
                {
                    xlRange = (Excel.Range)xlSheet.Cells[row, col];
                    xlRange.Font.Name = "MS Sans Serif";
                    xlRange.Font.Size = 10;
                    xlRange.Borders.Color = System.Drawing.Color.LightGray;

                    if (Dc.DataType == typeof(double) || Dc.DataType == typeof(float))
                    {
                        try
                        {
                            xlSheet.Cells[row, col] = Dr[col - 1];
                            xlRange.NumberFormat = "#,##0.00";
                        }
                        catch (System.Runtime.InteropServices.COMException ex)
                        {
                            message = ex.Message;
                            Dispose();

                            return false;
                        }
                    }
                    else if (Dc.DataType == typeof(int) || Dc.DataType == typeof(short) || Dc.DataType == typeof(ushort) ||
                        Dc.DataType == typeof(uint) || Dc.DataType == typeof(long) || Dc.DataType == typeof(ulong) ||
                        Dc.DataType == typeof(decimal))
                    {
                        try
                        {
                            xlSheet.Cells[row, col] = Dr[col - 1];
                            xlRange.NumberFormat = "#,##0";
                        }
                        catch (System.Runtime.InteropServices.COMException ex)
                        {
                            message = ex.Message;
                            Dispose();

                            return false;
                        }
                    }
                    else if (Dc.DataType == typeof(DateTime))
                    {
                        try
                        {
                            xlSheet.Cells[row, col] = Dr[col - 1];
                        }
                        catch (System.Runtime.InteropServices.COMException ex)
                        {
                            message = ex.Message;
                            Dispose();

                            return false;
                        }
                    }
                    else if (Dc.DataType == typeof(bool))
                    {
                        try
                        {
                            xlSheet.Cells[row, col] = Dr[col - 1];
                        }
                        catch (System.Runtime.InteropServices.COMException ex)
                        {
                            message = ex.Message;
                            Dispose();

                            return false;
                        }
                    }
                    else if (Dc.DataType == typeof(sbyte) || Dc.DataType == typeof(byte) || Dc.DataType == typeof(byte[]))
                    {
                        try
                        {
                            xlSheet.Cells[row, col] = null;
                        }
                        catch (System.Runtime.InteropServices.COMException ex)
                        {
                            message = ex.Message;
                            Dispose();

                            return false;
                        }
                    }
                    else
                    {
                        try
                        {
                            xlSheet.Cells[row, col] = (!string.IsNullOrEmpty(Dr[col - 1].ToString())) ? string.Format("'{0}", Dr[col - 1]) : null;
                        }
                        catch (System.Runtime.InteropServices.COMException ex)
                        {
                            message = ex.Message;
                            Dispose();

                            return false;
                        }
                    }

                    col++;
                }

                rowCount++;
                row++;
            }

            return true;
        }

        public string Message
        {
            get { return message; }
        }

        public void Dispose()
        {
            if (xlApp != null)
            {
                xlApp.Quit();

                System.Runtime.InteropServices.Marshal.ReleaseComObject(xlRange);
                System.Runtime.InteropServices.Marshal.ReleaseComObject(xlBook);
                System.Runtime.InteropServices.Marshal.ReleaseComObject(xlApp);

                GC.SuppressFinalize(xlRange);
                GC.SuppressFinalize(xlBook);
                GC.SuppressFinalize(xlApp);
                GC.Collect();

                xlRange = null;
                xlBook = null;
                xlApp = null;
            }
        }
    }
}