WinForm c# GridView导出Excel

WinForm GridView导出Excel
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.IO;

namespace gridview导出excel
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        SqlConnection con = new SqlConnection("server=.;database=TestDB;uid=sa;pwd=");
        private void btnSelect_Click(object sender, EventArgs e)
        {
            string Sql = "SELECT UserName,UserAge,UserPhone,UserAddress From tb_userinfo";
            con.Open();
            SqlDataAdapter da;
            da = new SqlDataAdapter(Sql, con);
            DataSet ds = new DataSet();
            da.Fill(ds, "tb_userinfo");
            this.dataGridView1.DataSource = ds.Tables["tb_userinfo"].DefaultView;


            con.Close();
        }

        private void btnOut_Click(object sender, EventArgs e)
        {
            SaveFileDialog saveFileDialog = new SaveFileDialog();
            saveFileDialog.Filter = "Execl   files   (*.xls)|*.xls";
            saveFileDialog.FilterIndex = 0;
            saveFileDialog.RestoreDirectory = true;
            saveFileDialog.CreatePrompt = true;
            saveFileDialog.Title = "导出Excel文件到";

            DateTime now = DateTime.Now;
            saveFileDialog.FileName = now.Year.ToString().PadLeft(2)
            + now.Month.ToString().PadLeft(2, '0')
            + now.Day.ToString().PadLeft(2, '0') + "-"
            + now.Hour.ToString().PadLeft(2, '0')
            + now.Minute.ToString().PadLeft(2, '0')
            + now.Second.ToString().PadLeft(2, '0');

            saveFileDialog.ShowDialog();

            Stream myStream;
            myStream = saveFileDialog.OpenFile();
            StreamWriter sw = new StreamWriter(myStream, System.Text.Encoding.GetEncoding("gb2312"));
            string str = "";
            try
            {
                //写标题     
                for (int i = 0; i < dataGridView1.ColumnCount; i++)
                {
                    if (i > 0)
                    {
                        str += "\t";
                    }
                    str += dataGridView1.Columns[i].HeaderText;
                }

                sw.WriteLine(str);
                //写内容   
                for (int j = 0; j < dataGridView1.Rows.Count; j++)
                {
                    string tempStr = "";
                    for (int k = 0; k < dataGridView1.Columns.Count; k++)
                    {
                        if (k > 0)
                        {
                            tempStr += "\t";
                        }
                        tempStr += dataGridView1.Rows[j].Cells[k].Value.ToString();
                    }
                    sw.WriteLine(tempStr);
                }
                sw.Close();
                myStream.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
            finally
            {
                sw.Close();
                myStream.Close();
            }
        }

    }


}