using System;

using System.IO;

using System.Windows.Forms;

​

namespace WindowsFormsApp11

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

​

        private void Form1_Load(object sender, EventArgs e)

        {

            // enter default path

            string path = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);

            textBox1.Text = path;

        }

​

        private void buttonReadDir_Click(object sender, EventArgs e)

        {

            string path = textBox1.Text;

​

            //DirectoryInfo dir = new DirectoryInfo(path);

            //var files = dir.GetFiles();

            string[] files = Directory.GetFiles(path);

​

            foreach (var file in files)

            {

                var fi = new FileInfo(file);

                listBox1.Items.Add(fi);

            }

        }

​

        private async void button1_Click(object sender, EventArgs e)

        {

            var fi = listBox1.SelectedItem as FileInfo;

​

            if (fi == null) return;

​

            // use using(){...} instead of Close()

            //var sr = File.OpenRead(fi.FullName);

            using (var sr = fi.OpenText())

            {

                string text = await sr.ReadToEndAsync();

                textBox2.Text = text;

            }

        }

​

        private async void button2_Click(object sender, EventArgs e)

        {

            var fi = listBox1.SelectedItem as FileInfo;

​

            if (fi == null) return;

​

            string path = fi.FullName;

            string text = textBox2.Text;

​

            //var fs = new FileStream(path, FileMode.Open);

            //var bytes = Encoding.UTF8.GetBytes(text);

            //await fs.WriteAsync(bytes, 0, bytes.Length);

            //fs.Close();

​

            using (var sw = new StreamWriter(path))

                await sw.WriteAsync(text);

        }

    }

}

​