一个通用的DataGridView导出Excel扩展方法(支持列数据格式化)

假如数据库表中某个字段存放的值“1”和“0”分别代表“是”和“否”，要在DataGridView中显示“是”和“否”，一般用两种方法，一种是在sql中直接判断获取，另一种是在DataGridView的CellFormatting事件中设置。
下面介绍的是第二种情况下的处理。
举个例子，DataGridView的第4列需要在金额后面加个“元”，在第14列根据1和0显示为相应的是和否，在显示的时候可以这样设置：

private void dgData_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
        {
       if (e.ColumnIndex == 3)
            {
                if (e.Value != null)
                    e.Value = e.Value.ToString() + "元";
            }
            if (e.ColumnIndex == 13)
            {
                if (e.Value != null)
                    e.Value = e.Value.ToString() == "1" ? "是" : "否";
            }
        }

 但是在循环行列导出Excel的时候并不会得到格式化后的数据，需要在循环列时判断是哪一列，再调用方法格式化列，如下：

private string FormatRMB(string s)
        {
            return s + "元";
        }
        private string FormatStatu(string s)
        {
            return s == "1" ? "已放款" : "未放款";
        }

        private void ToExcel(int columnIndex, string fileName)
        {
            List<int> indexList = dgData.CheckBoxSelect(0);
            if (indexList.Count == 0)
            {
                MessageBox.Show("请先选择！");
                return;
            }
            using (SaveFileDialog saveFileDialog = new SaveFileDialog())
            {
                saveFileDialog.Title = "导出Excel文件到";
                saveFileDialog.Filter = "Execl files(*.xls)|All Files(*.*)";
                saveFileDialog.FileName = fileName;
                saveFileDialog.AddExtension = true;
                saveFileDialog.RestoreDirectory = true;
                if (saveFileDialog.ShowDialog() == DialogResult.OK)
                {
                    IWorkbook workbook = new HSSFWorkbook();
                    ISheet sheet = workbook.CreateSheet();
                    IRow rowTitle = sheet.CreateRow(0);
                    for (int j = columnIndex; j < dgData.Columns.Count; j++)
                    {
                        string headerText = dgData.Columns[j].HeaderText;
                        rowTitle.CreateCell(j - 1).SetCellValue(headerText);
                    }
                    for (int i = 0; i < indexList.Count; i++)
                    {
                        int selRowIndex = indexList[i];
                        IRow row = sheet.CreateRow(i + 1);
                        for (int j = columnIndex; j < dgData.Columns.Count; j++)
                        {
                            string val = dgData.Rows[selRowIndex].Cells[j].Value == null ? "" : dgData.Rows[selRowIndex].Cells[j].Value.ToString();
                            //格式化列数据
                            if (j == 3)
                                val = FormatRMB(val);
                            else if (j == 13)
                                val = FormatStatu(val);
                         
                            row.CreateCell(j - 1).SetCellValue(val);
                        }
                    }
                    FileStream outFs = new FileStream(saveFileDialog.FileName, FileMode.Create);
                    workbook.Write(outFs);
                    outFs.Close();
                }
            }
        }

这里有一个缺点就是这个导出的方法失去了通用性，其它页面调用不了。
解决方法是在这个导出方法中再传一个字典参数，存放要格式化的列索引和委托，当循环到这一列时就执行这一个委托方法。
如下所示，现在已经是一个通用的方法，放在一个静态类中作为扩展方法，调用：

private void btnToExcel_Click(object sender, EventArgs e)
        {
            string fileName = string.Format("test_{0}.xls", DateTime.Now.ToString("yyyyMMddHHmmss"));
            Dictionary<int, Func<string, string>> dict = new Dictionary<int, Func<string, string>>();
            dict.Add(3, FormatRMB);
            dict.Add(13, FormatStatu);           
            dgData.ExportExcel(1, fileName, dict);          
        }

//引用NPOI.dll
//using NPOI.SS.UserModel;
//using NPOI.HSSF.UserModel;

    public static class Extenstions
    {
        /// <summary>
        /// Excel导出
        /// </summary>
        /// <param name="dgv">DataGridView控件ID</param>
        /// <param name="columnIndex">从哪一列开始导出(因为有些列是checkbox)</param>
        /// <param name="fileName">保存的文件名</param>
        /// <param name="dict">存储列数据格式化的列号与方法字典</param>
        public static void ExportExcel(this DataGridView dgv, int columnIndex, string fileName, Dictionary<int, Func<string, string>> dict)
        {
            List<int> indexList = dgv.CheckBoxSelect(0);
            if (indexList.Count == 0)
            {
                MessageBox.Show("请先选择！");
                return;
            }
            using (SaveFileDialog saveFileDialog = new SaveFileDialog())
            {
                saveFileDialog.Title = "导出Excel文件到";
                saveFileDialog.Filter = "Execl files(*.xls)|All Files(*.*)";
                saveFileDialog.FileName = fileName;
                saveFileDialog.AddExtension = true;
                saveFileDialog.RestoreDirectory = true;
                if (saveFileDialog.ShowDialog() == DialogResult.OK)
                {
                    IWorkbook workbook = new HSSFWorkbook();
                    ISheet sheet = workbook.CreateSheet();
                    IRow rowTitle = sheet.CreateRow(0);
                    for (int j = columnIndex; j < dgv.Columns.Count; j++)
                    {
                        string headerText = dgv.Columns[j].HeaderText;
                        rowTitle.CreateCell(j - 1).SetCellValue(headerText);
                    }
                    for (int i = 0; i < indexList.Count; i++)
                    {
                        int selRowIndex = indexList[i];
                        IRow row = sheet.CreateRow(i + 1);
                        for (int j = columnIndex; j < dgv.Columns.Count; j++)
                        {
                            string val = dgv.Rows[selRowIndex].Cells[j].Value == null ? "" : dgv.Rows[selRowIndex].Cells[j].Value.ToString();
                            //格式化列数据
                            if (dict.ContainsKey(j))
                            {
                                var v = dict.First(t => t.Key == j).Value;
                                val = v(val);
                            }
                            row.CreateCell(j - 1).SetCellValue(val);
                        }
                    }
                    FileStream outFs = new FileStream(saveFileDialog.FileName, FileMode.Create);
                    workbook.Write(outFs);
                    outFs.Close();
                }
            }
        }
   }