Winform中datagridview导出Excel

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.Data.SqlClient;

namespace ExportExcel
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnExcel_Click(object sender, EventArgs e)
        {
            SaveAs();
        }
        private void SaveAs() //另存新档按钮   导出成Excel
        {    
            SaveFileDialog saveFileDialog = new SaveFileDialog();
            saveFileDialog.Filter = "Execl files (*.xls)|*.xls";
            saveFileDialog.FilterIndex = 0;
            saveFileDialog.RestoreDirectory = true;
            saveFileDialog.CreatePrompt = true;
            saveFileDialog.Title = "Export Excel File To";
            DialogResult result =  saveFileDialog.ShowDialog();
            Stream myStream;
            if (result == DialogResult.Cancel)
            {
                return;
            }
            else
            {
                myStream = saveFileDialog.OpenFile();
            }
           
            StreamWriter sw = new StreamWriter(myStream, System.Text.Encoding.GetEncoding(-0));
            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 e)
            {
                MessageBox.Show(e.ToString());
            }
            finally
            {
                sw.Close();
                myStream.Close();
            }
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            string sql = "select * from [user]";
            SqlConnection con = new SqlConnection(@"Data Source=.\sqlexpress;Initial Catalog=Test;Integrated Security=True");
            SqlCommand com = new SqlCommand(sql,con);
            DataSet ds = new DataSet();
            SqlDataAdapter sda = new SqlDataAdapter();
            sda.SelectCommand = com;
            sda.Fill(ds);
            this.dataGridView1.DataSource = ds.Tables[0];

this.dataGridView1.AllowUserToAddRows = false;//不允许用户添加行，如果设置为true，遍历DataGridView时会把最后一条允许用户添加的行算进去，容易导致空指针异常
            con.Close();
        }
    }
}