c# 使用NPOI将DataTable 写入Excel 中的数据类型转换

using System;
using System.Data;
using NPOI.SS.UserModel;
using NPOI.XSSF.UserModel;

public class ExcelWriter
{
    public static void WriteDataTableToExcel(DataTable dataTable, string filePath)
    {
        // 创建一个新的工作簿
        IWorkbook workbook = new XSSFWorkbook();
        // 创建一个工作表
        ISheet sheet = workbook.CreateSheet("Sheet1");

        // 创建标题行
        IRow headerRow = sheet.CreateRow(0);
        for (int i = 0; i < dataTable.Columns.Count; i++)
        {
            headerRow.CreateCell(i).SetCellValue(dataTable.Columns[i].ColumnName);
        }

        // 填充数据行
        int rowIndex = 1;
        foreach (DataRow row in dataTable.Rows)
        {
            IRow dataRow = sheet.CreateRow(rowIndex++);
            for (int i = 0; i < dataTable.Columns.Count; i++)
            {
                DataColumn column = dataTable.Columns[i];
                ICell cell = dataRow.CreateCell(i);

                switch (column.DataType.Name.ToLower())
                {
                    case "string":
                        cell.SetCellValue(row[i].ToString());
                        break;
                    case "int32":
                    case "int64":
                        cell.SetCellValue(Convert.ToInt32(row[i]));
                        break;
                    case "double":
                        cell.SetCellValue(Convert.ToDouble(row[i]));
                        break;
                    case "datetime":
                        cell.SetCellValue(Convert.ToDateTime(row[i]));
                        break;
                    case "boolean":
                        cell.SetCellValue(Convert.ToBoolean(row[i]));
                        break;
                    default:
                        cell.SetCellValue(row[i].ToString());
                        break;
                }
            }
        }

        // 将工作簿写入文件
        using (var fs = new FileStream(filePath, FileMode.Create, FileAccess.Write))
        {
            workbook.Write(fs);
        }
    }
}

或者：

public static void CreateSheet(IWorkbook workbook, DataTable dt, int num)
{
    ISheet sheet = string.IsNullOrEmpty(dt.TableName) ? workbook.CreateSheet("Sheet" + num) : workbook.CreateSheet(dt.TableName);

    ICellStyle style = workbook.CreateCellStyle();//设置表格样式
    style.BorderBottom = BorderStyle.Thin;//下边框线（给表格加入背景颜色后，就会覆盖原来的边框，直接设置边框样式可以解决这一问题）
    style.BorderLeft = BorderStyle.Thin; //左边框线
    style.BorderRight = BorderStyle.Thin;//右边框线
    style.BorderTop = BorderStyle.Thin;//上边框线

    sheet.PrintSetup.PaperSize = 9;//A4纸张打印
    sheet.PrintSetup.Landscape = true;//横向打印（默认为false即竖向）

    //设置自动调整为一页宽度
    sheet.Autobreaks = false;//必须设置
    sheet.FitToPage = true; //一页宽   
    sheet.PrintSetup.FitWidth = 1;
    sheet.PrintSetup.FitHeight = short.MaxValue;

    //表头  
    IRow row = sheet.CreateRow(0);
    for (int i = 0; i < dt.Columns.Count; i++)
    {
        ICell cell = row.CreateCell(i);
        cell.SetCellValue(dt.Columns[i].ColumnName);
        cell.CellStyle = style;
    }

    //数据  
    for (int i = 0; i < dt.Rows.Count; i++)
    {
        IRow row1 = sheet.CreateRow(i + 1);
        for (int j = 0; j < dt.Columns.Count; j++)
        {
            ICell cell = row1.CreateCell(j);
            cell.CellStyle = style;

            if (dt.Columns[j].DataType.Equals(typeof(bool)) && bool.TryParse(dt.Rows[i][j].ToString(), out bool b))
            {
                cell.SetCellValue(b);
            }
            else if (double.TryParse(dt.Rows[i][j].ToString(), out double d))//数字格式
            {
                cell.SetCellValue(d);
            }
            else
            {
                cell.SetCellValue(dt.Rows[i][j].ToString());
            }
        }
    }

    for (int columnIndex = 0; columnIndex < dt.Rows.Count; columnIndex++)
    {
        sheet.AutoSizeColumn(columnIndex); //列宽自适应
    }

}