Form1.cs

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 WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            for (int i = 0; i < 10; ++i)
            {
                exampleListBox.Items.Add(i);
            }

        }

        private void exampleButton_Click(object sender, EventArgs e)
        {
            exampleListBox.Items[exampleListBox.SelectedIndex] = exampleListBox.Items[exampleListBox.SelectedIndex];
        }

        private void exampleListBox_SelectedIndexChanged(object sender, EventArgs e)
        {
            Console.WriteLine(exampleListBox.SelectedIndex);
        }
    }
}