string保存成TXT文件

// <summary>
        /// 检查是否存在文件夹
        /// </summary>
        public void change()
        {
            string path = Application.StartupPath + "\\" + DateTime.Now.ToString("yyyy-MM-dd") + "\\TextMessage.txt";
            if (!Directory.Exists(Application.StartupPath + "\\" + DateTime.Now.ToString("yyyy-MM-dd")))
            {
                Directory.CreateDirectory(Application.StartupPath + "\\" + DateTime.Now.ToString("yyyy-MM-dd"));
            }

            if (!File.Exists(path))
            {
                FileStream fs = File.Create(@"" + DateTime.Now.ToString("yyyy-MM-dd") + "\\TextMessage.txt");
                fs.Close();
            }

        }
        /// <summary>
        /// 写入文本文件
        /// </summary>
        /// <param name="value"></param>
        public void text(string value)
        {

            change();
            string path = Application.StartupPath + "\\" + DateTime.Now.ToString("yyyy-MM-dd") + "\\TextMessage.txt";
            FileStream f = new FileStream(path, FileMode.Append, FileAccess.Write, FileShare.ReadWrite);
            StreamWriter sw = new StreamWriter(f);
            sw.WriteLine(value);
            sw.Flush();
            sw.Close();
            f.Close();
        }