c# npoi excel 如何获取单元格的公式VALUE

csharp
using System;
using System.IO;
using NPOI.SS.UserModel;
using NPOI.XSSF.UserModel;
using NPOI.HSSF.UserModel;
namespace excelFormulaValue
{
    class Program
    {
        static void MAIn(string[] args)
        {
            string filePath = "路径/文件名.xlsx";
            IWorkbook workbook;
            using (FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read))
            {
                if (Path.GetExtension(filePath) == ".xlsx")
                {
                    workbook = new XSSFWorkbook(fileStream);
                }
                else if (Path.GetExtension(filePath) == ".xls")
                {
                    workbook = new HSSFWorkbook(fileStream);
                }
                else
                {
                    throw new Exception("不支持的文件格式");
                }
            }
            ISheet sheet = workbook.GetSheetAt(0); // 获取第一个工作表
            int rowIndex = 1; // 行索引
            int columnIndex = 1; // 列索引
            IRow row = sheet.GetRow(rowIndex);
            ICell cell = row.Getcell(columnIndex);
            if (cell.CellType == CellType.Formula)
            {
                string formula = cell.CellFormula;
                cell = sheet.GetRow(rowIndex).Getcell(columnIndex);
                cell.SetcellType(CellType.String);
                string value = cell.StringCellValue;
                Console.WriteLine("公式：" + formula);
                Console.WriteLine("值：" + value);
            }
            else
            {
                string value = cell.ToString();
                Console.WriteLine("值：" + value);
            }
            Console.ReadLine();
        }
    }
}