1.添加NOPI

        引用->管理NuGet程序包->添加NOPI

2.相关程序集

3.添加命名空间

using NPOI.HSSF;
using NPOI.XSSF;
using System.IO;
using NPOI.XSSF.UserModel;
using NPOI.HSSF.UserModel;

4.从Excel导入的dgv样例

//NPOI读入dgv
private void button1_Click(object sender, EventArgs e)
{DataTable dtNpoi = new DataTable();string fileName = @"D:\desktop\tmp\test.xlsx";string sheetName = "sheet1";bool isColumnName = true;IWorkbook workBook;string fileExt = Path.GetExtension(fileName).ToLower(); //获取文件拓展名using (FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read)){if(fileExt == ".xlsx")  //新版{workBook = new XSSFWorkbook(fs);}else if(fileExt == ".xls")  //旧版{workBook = new HSSFWorkbook(fs);}else{workBook=null;}//实例化sheet（指定名称没加载出来就通过索引加载sheet）ISheet sheet = null;if(sheetName != null &&  sheetName.Length > 0) {sheet = workBook.GetSheet(sheetName);   //获取指定名称的工作表if(sheet == null ){sheet = workBook.GetSheetAt(0); //工作簿没有内容，通过索引0返回空worksheet对象，不会null报错}}else{sheet = workBook.GetSheetAt(0); //获取第一个工作表}//获取表头FirstRowNum第一行索引就是0IRow header = sheet.GetRow(sheet.FirstRowNum);  //获取第一行int startRow = 0;  //数据的第一行索引if(isColumnName)    //表示第一行是列名信息{startRow = sheet.FirstRowNum + 1;   //第一行应该是从1开始的//遍历第一行的单元格 列名 0for (int i = header.FirstCellNum; i < header.LastCellNum; i++){//获取指定索引单元格ICell cell = header.GetCell(i);if(cell != null){//获取列名的值string cellValue = cell.ToString();if(cellValue != null){DataColumn col = new DataColumn(cellValue); //记住可以这样子添加dtNpoi.Columns.Add(col);}else{DataColumn col = new DataColumn();dtNpoi.Columns.Add(col);}}}}//数据    LastRowNum最后一行的索引 如第九行索引是8for (int i = startRow; i <= sheet.LastRowNum; i++){IRow row = sheet.GetRow(i); //获取第i行if(row == null ){continue;}DataRow dr = dtNpoi.NewRow();//遍历每行的单元格for (int j = row.FirstCellNum; j < row.LastCellNum; j++){if(row.GetCell(j) != null)dr[j] = row.GetCell(j).ToString();}dtNpoi.Rows.Add(dr);}}this.dataGridView1.DataSource = dtNpoi;}

5.从dgv导入到Excel

DataTable dtTable = this.dataGridView1.DataSource as DataTable; //表1转换为DataTable
string sheetName = "sheet1";
//创建工作簿
IWorkbook wb = new HSSFWorkbook();
//这个创建sheet很巧妙
ISheet sheet = string.IsNullOrEmpty(sheetName) ? wb.CreateSheet("sheet1") : wb.CreateSheet(sheetName);
int rowIndex = 0;
if(dtTable.Columns.Count > 0)
{IRow header = sheet.CreateRow(rowIndex);    //创建第一行for (int i = 0; i < dtTable.Columns.Count; i++){ICell cell = header.CreateCell(i);  //给第一行赋值cell.SetCellValue(dtTable.Columns[i].ColumnName);}
}//添加数据
if(dtTable.Rows.Count > 0)
{for (int i = 0; i < dtTable.Rows.Count; i++){rowIndex++;IRow row = sheet.CreateRow(rowIndex);for (int j = 0; j < dtTable.Columns.Count; j++){ICell cell = row.CreateCell(j);cell.SetCellValue(dtTable.Rows[i][j].ToString());}}
}//列的大小为自动
for (int i = 0; i < dtTable.Columns.Count; i++)
{//sheet.AutoSizeColumn(i);
}string fileName = @"D:\desktop\tmp\NPOI导出.xls";
using(FileStream fs = new FileStream(fileName, FileMode.Create, FileAccess.Write))
{wb.Write(fs);   //这个workbook竟然可以直接写
}MessageBox.Show("导出成功！");