C# winform 如何实现在计算机指定路径保存和调取文件

比如这次用户输入一段文字，点击按钮就会在指定路径生成一个文件保存这段文字，然后下次打开软件这段文字也不会消失。
入门级菜鸟请教，请大神说仔细点，最好能举个小例子。小弟感激不尽！

 //引用 system.io
        string path = "e://测试.txt";//这是路径
        private void btnWrite_Click(object sender, EventArgs e)
        {
            if (txtWrite.Text != "")
            {
                using (FileStream fs = File.Open(path, FileMode.Create, FileAccess.Write))
                {
                    using (StreamWriter sw = new StreamWriter(fs, Encoding.Default))
                    {
                        sw.WriteLine(txtWrite.Text);//把文本框里东西写进去

                    }
                }
            }
        }

        private void btnRead_Click(object sender, EventArgs e)
        {
            using (FileStream fs = File.Open(path, FileMode.Open, FileAccess.Read))
            {
                using (StreamReader sr = new StreamReader(fs, Encoding.Default))
                {
                    while (!sr.EndOfStream)
                    {
                        txtRead.Text = sr.ReadLine();//读到txtread文本框
                    }
                }
            }
        }