c sharp listbox recherche

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;
using System.Collections;

namespace TriListe
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        int i,j;

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void textBox1_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyData == Keys.Enter)
            {
                listBox1.Items.Add(textBox1.Text);
                textBox1.Clear();

            }
        }

        private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {

        }

        private void Rechercher(object sender, EventArgs e)
        {
            for (i = 0; i < listBox1.Items.Count; i++)
            {
                string s = listBox1.Items[i].ToString();

                if (s.Contains(textBox2.Text))
                {
                    MessageBox.Show("Element trouvé " + i);

                }
            }
        }
    }
}