dataGridView读写入文本

   constant con = new constant();

        private void loadlistbox2()
        {
            dataGridView1.ColumnCount = 1;
            string z;
            if (File.Exists(".//allitems.txt"))
            {
                FileStream fs = new FileStream(".//allitems.txt", System.IO.FileMode.Open, System.IO.FileAccess.Read);

                StreamReader sr = new StreamReader(fs, System.Text.Encoding.GetEncoding("utf-8"));
                try
                {
                    while (true)
                    {
                        z = sr.ReadLine();
                        if (z == null) break;
                        dataGridView1.Rows.Add(z);
                    }
                }
                finally
                {
                    sr.Close();
                    fs.Dispose();
                    fs.Close();
                }
            }
        }
        string st = "";

private void savetestitem()
        {
           // dataGridView1.ColumnCount = 1;
            if (File.Exists(".//allitems.txt"))
            {
                FileStream fs = new FileStream(".//allitems.txt", System.IO.FileMode.Open, System.IO.FileAccess.Write);

                StreamWriter sr = new StreamWriter(fs, System.Text.Encoding.GetEncoding("utf-8"));
                try
                {
                    for (int i = 0; i < 22; i++)
                    {
                        for (int j = 0; j < 1; j++)
                        {
                            st = st + dataGridView1.Rows[i].Cells[j].Value;
                        }
                        sr.WriteLine(st);
                        st = "";

                        //for (int i = 0; i < dataGridView1.Rows.Count; i++)
                        //{
                        //        sr.WriteLine(dataGridView1.Rows[i].Cells);
                        //    }
                       }

                    }              
                finally
                {
                    sr.Close();
                    fs.Dispose();
                    fs.Close();
                }
            }
        }