winform 向excel中追加sheet

/// <summary>
        /// 通过DataTable向一个现有的excel表中增加一个sheet
        /// </summary>
        /// <param name="dt">带有数据集的DataTable</param>
        /// <param name="toFileName">现有excel的路径以及名称</param>
        /// <param name="strSheetName">需要添加的Sheet的名字</param>
        private void doExport(DataTable dt, string toFileName, string strSheetName)
        {
            Microsoft.Office.Interop.Excel.Application excel = new Microsoft.Office.Interop.Excel.Application();  //Execl的操作类
            //读取保存目标的对象
            Microsoft.Office.Interop.Excel.Workbook bookDest = excel.Workbooks._Open(toFileName, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value);
            //打开要导出到的Execl文件的工作薄。--ps:关于Missing类在这里的作用，我也不知道...囧
            Microsoft.Office.Interop.Excel.Worksheet sheetDest = bookDest.Worksheets.Add(Missing.Value, Missing.Value, Missing.Value, Missing.Value) as Microsoft.Office.Interop.Excel.Worksheet;
            //给工作薄添加一个Sheet
            sheetDest.Name = strSheetName;//自己定义名字O(∩_∩)O哈哈~
            int rowIndex = 1;
            int colIndex = 0;
            excel.Application.Workbooks.Add(true);//这句不写不知道会不会报错
            Microsoft.Office.Interop.Excel.Range range = null;

            foreach (DataColumn col in dt.Columns)
            {

                colIndex++;
                sheetDest.Cells[1, colIndex] = col.ColumnName;//Execl中的第一列,把DataTable的列名先导进去
                sheetDest.get_Range(sheetDest.Cells[1, 1], sheetDest.Cells[1, dt.Columns.Count]).HorizontalAlignment = Microsoft.Office.Core.XlHAlign.xlHAlignCenterAcrossSelection;
                range = (Microsoft.Office.Interop.Excel.Range)sheetDest.Cells[1, colIndex];
                range.BorderAround(Microsoft.Office.Interop.Excel.XlLineStyle.xlContinuous, Microsoft.Office.Interop.Excel.XlBorderWeight.xlThin,
                               Microsoft.Office.Interop.Excel.XlColorIndex.xlColorIndexAutomatic, null);
                range.Font.Bold = true; //粗体
            }

            #region
            //导入数据行
            //foreach (DataRow row in dt.Rows)
            //{
            //    rowIndex++;
            //    colIndex = 0;
            //    foreach (DataColumn col in dt.Columns)
            //    {
            //        colIndex++;
            //        sheetDest.Cells[rowIndex, colIndex] = row[col.ColumnName].ToString();
            //    }
            //}
            #endregion
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                DataRow row = dt.Rows[i];
                for (int j = 0; j < dt.Columns.Count; j++)
                {
                    DataColumn col = dt.Columns[j];
                    sheetDest.Cells[i + 2, j + 1] = row[col.ColumnName].ToString();
                    range = (Microsoft.Office.Interop.Excel.Range)sheetDest.Cells[i + 2, j + 1];
                    range.BorderAround(Microsoft.Office.Interop.Excel.XlLineStyle.xlContinuous, Microsoft.Office.Interop.Excel.XlBorderWeight.xlThin,
                                   Microsoft.Office.Interop.Excel.XlColorIndex.xlColorIndexAutomatic, null);
                }
            }
            sheetDest.Columns.EntireColumn.AutoFit();//列宽自适应
            if (toFileName.ToLower().Contains("wish"))
            {
                sheetDest.get_Range(sheetDest.Cells[1, 1], sheetDest.Cells[dt.Rows.Count + 1, dt.Columns.Count - 5]).HorizontalAlignment = Microsoft.Office.Core.XlHAlign.xlHAlignCenterAcrossSelection;
            }
            else
            {
                sheetDest.get_Range(sheetDest.Cells[1, 1], sheetDest.Cells[dt.Rows.Count + 1, dt.Columns.Count - 4]).HorizontalAlignment = Microsoft.Office.Core.XlHAlign.xlHAlignCenterAcrossSelection;
            }
            bookDest.Saved = true; bookDest.Save();
            excel.Quit();
            excel = null;
            GC.Collect();//垃圾回收
        }