c#怎么选择多个文件——代码实现

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace selectFiles
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            OpenFileDialog dlg = new OpenFileDialog();
            dlg.Multiselect = true;
            dlg.DefaultExt = ".txt";
            dlg.Filter = "记事本文件|*.txt";
            if (dlg.ShowDialog() == DialogResult.OK)
            {
                var sb = new StringBuilder();
                foreach (string file in dlg.FileNames) {
                    sb.Append(file);
                    sb.Append("\r\n");
                }
                textBox1.Text = sb.ToString();
            }
        }
    }
}