datagridview导出Excel(以流的方式)

 private void ExportToExcel()
        {
            SaveFileDialog saveFileDialog = new SaveFileDialog();
            saveFileDialog.Filter = "Execl files (*.xls)|*.xls";
            saveFileDialog.FilterIndex = 0;
            saveFileDialog.RestoreDirectory = true;
            saveFileDialog.CreatePrompt = true;
            saveFileDialog.Title = "保存为Excel文件";
            saveFileDialog.ShowDialog();

            if (saveFileDialog.FileName.IndexOf(":") < 0) return; //被点了"取消"

            Stream myStream;
            myStream = saveFileDialog.OpenFile();
            StreamWriter sw = new StreamWriter(myStream, System.Text.Encoding.GetEncoding(-0));
            string columnTitle = "";
            try
            {
                //写入列标题
                for (int i = 0; i < dgvGF_IN_INFO.ColumnCount; i++)
                {
                    if (i > 0)
                    {
                        columnTitle += "\t";
                    }
                    columnTitle += dgvGF_IN_INFO.Columns[i].HeaderText;
                }
                sw.WriteLine(columnTitle);

                //写入列内容
                for (int j = 0; j < dgvGF_IN_INFO.Rows.Count; j++)
                {
                    string columnValue = "";
                    for (int k = 0; k < dgvGF_IN_INFO.Columns.Count; k++)
                    {
                        if (k > 0)
                        {
                            columnValue += "\t";
                        }
                        if (dgvGF_IN_INFO.Rows[j].Cells[k].Value == null)
                            columnValue += "";
                        else
                            columnValue += dgvGF_IN_INFO.Rows[j].Cells[k].Value.ToString().Trim();
                    }
                    sw.WriteLine(columnValue);
                }
                sw.Close();
                myStream.Close();
            }
            catch (Exception e)
            {
                MessageBox.Show(e.ToString());
            }
            finally
            {
                sw.Close();
                myStream.Close();
            }
        }