C# winform写入和读取TXT文件

string str;

            str=this.textBox1.Text;

            StreamWriter sw = new StreamWriter(Application.StartupPath +"\\txtwriter.txt", false);

            sw.WriteLine(str);

            sw.Close();//写入

            string str;

            StreamReader sr = new StreamReader(Application.StartupPath +"\\txtreader.txt", false);

            str = sr.ReadLine().ToString();

            sr.Close();

            this.textBox1.Text = str;///读取