SaveFileDialog sfDialog = new SaveFileDialog();
            sfDialog.DefaultExt =".txt";
            string filename;
            if (sfDialog.ShowDialog() == DialogResult.OK)
            {
                filename = sfDialog.FileName;
                StreamWriter writer ;
                if (File.Exists(filename))
                {
                    writer = File.AppendText(filename);
                }
                else
                {
                    writer = File.CreateText(filename);
                }
                writer.WriteLine("hello world\n", Encoding.ASCII);
                writer.Flush();
                writer.Close();
            }


换行符号变成了乱吗.怎么改?谢谢高手