public partial class Form1 : Form
      {
        public Form1()
        {
            InitializeComponent();
        }
        /// <summary>
        /// 全局变量,用来存放TXT路径
        /// </summary>
        private string txtPath = String.Empty;

        /// <summary>
        /// 打开文本文档
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Btn_Opne_Click(object sender, EventArgs e)
        {
            openFileDialog1.ShowDialog();

            //得到文本路径，显示出来
            txtPath = openFileDialog1.FileName;

            if (txtPath == "") return;
            StreamReader sr = new StreamReader(txtPath, System.Text.Encoding.Default);
            string strText = sr.ReadToEnd();
            sr.Close();
            sr.Dispose();
            textBox1.Text = strText;
        }

        /// <summary>
        /// 保存文本
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Btn_Save_Click(object sender, EventArgs e)
        {
            WriteTxt(textBox1.Text, txtPath);
        }


        /// <summary>
        /// 写入
        /// </summary>
        /// <param name="strMemo">写入的字符串</param>
        /// <param name="path">文本所在的路径</param>
        public void WriteTxt(string strMemo, string path)
        {
            StreamWriter sw = new StreamWriter(path, true);
            sw.WriteLine(strMemo);
            sw.Flush();
            sw.Close();
            sw.Dispose();
        }
    }