将datagridview数据保为xml或txt文件

using System.IO
public void SaveFile()
        {
            //实例化一个保存文件对话框
            SaveFileDialog sf = new SaveFileDialog();
            //设置文件保存类型
            sf.Filter = "txt文件|*.txt|xml";
            //如果用户没有输入扩展名，自动追加后缀
            sf.AddExtension = true;
            //设置标题
            sf.Title = "写文件";
            //如果用户点击了保存按钮
            if (sf.ShowDialog() == DialogResult.OK)
            {
                //实例化一个文件流--->与写入文件相关联
                FileStream fs = new FileStream(sf.FileName, FileMode.Create);
                //实例化一个StreamWriter-->与fs相关联
                StreamWriter sw = new StreamWriter(fs);
                //开始写入
                if (this.dataGridView1.Rows.Count < 1)
                {
                    MessageBox.Show("没有数据！导出失败！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);

}
                else
                {
                    for (int i = 0; i < this.dataGridView1.Rows.Count - 1; i  )
                    {
                        sw.WriteLine(this.dataGridView1.Rows[i].Cells[0].Value.ToString());
                    }
                    //sw.Write(this.textBox1.Text);
                    //清空缓冲区
                    sw.Flush();
                    //关闭流
                    sw.Close();
                    fs.Close();
                    MessageBox.Show("保存成功！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
                }
            }
        }