test for FormatTypes in DatasetTable.PopulateTable about excellibrary HOT 3 OPEN

Workbook book = Workbook.Load(filename);
                Worksheet sheet = book.Worksheets[0];
                if (sheet.Cells.Rows.Count > 0)
                {
                    DataTable tab = new DataTable();
                    Row HeadRow = sheet.Cells.GetRow(0);
                    DataColumn dc;

                    //把第一行当成列标题  the First Row is ColumName
                    for (int a = 0; a < HeadRow.LastColIndex; a++)
                    {
                        dc = new DataColumn(HeadRow.GetCell(a).StringValue);
                        tab.Columns.Add(dc);
                    }
                    for (int rowIndex = sheet.Cells.FirstRowIndex + 1; rowIndex <= sheet.Cells.LastRowIndex; rowIndex++)
                    {
                        DataRow dr = tab.NewRow();
                        Row row = sheet.Cells.GetRow(rowIndex);
                        for (int colIndex = row.FirstColIndex; colIndex <= row.LastColIndex; colIndex++)
                        {
                            //Can not use row.GetCell(colIndex).Format.FormatType 
                            if (HeadRow.GetCell(colIndex).StringValue.IndexOf("日期") >= 0)
                            {
                                Double df = double.Parse(row.GetCell(colIndex).StringValue);
                                DateTime dt= DateTime.FromOADate(df);
                                dr[colIndex] = dt.ToString("yyyy-MM-dd HH:mm:ss");
                            }

                            else { dr[colIndex] = row.GetCell(colIndex).StringValue; }
                        }
                        tab.Rows.Add(dr);
                    }
                    book = null;
                    sheet = null;
                    dgv.DataSource = tab;