使用NPOI从Excel中的单元格获取完整的日期和时间值

using System;
using NPOI.HSSF.UserModel; // For xls files
using NPOI.XSSF.UserModel; // For xlsx files
using NPOI.SS.UserModel;

public class ExcelReader
{
    public DateTime GetDateTimeValueFromCell(string filePath, string sheetName, int rowIndex, int columnIndex)
    {
        IWorkbook workbook;
        ISheet sheet;
        IRow row;
        ICell cell;

        using (var fs = new FileStream(filePath, FileMode.Open, FileAccess.Read))
        {
            // Determine the format of the Excel file (xls or xlsx) and create the appropriate workbook instance
            if (Path.GetExtension(filePath) == ".xls")
                workbook = new HSSFWorkbook(fs);
            else if (Path.GetExtension(filePath) == ".xlsx")
                workbook = new XSSFWorkbook(fs);
            else
                throw new ArgumentException("Invalid file format");

            // Get the specified sheet by name
            sheet = workbook.GetSheet(sheetName);

            // Get the specified row and cell
            row = sheet.GetRow(rowIndex);
            cell = row.GetCell(columnIndex);

            // Get the cell's value
            object cellValue = null;

            if (cell.CellType == CellType.Numeric && DateUtil.IsCellDateFormatted(cell))
            {
                cellValue = cell.DateCellValue; // Get the date value from the cell
            }
            else
            {
                throw new ArgumentException("Cell does not contain a date and time value");
            }

            return (DateTime)cellValue;
        }
    }
}