VisualComponents/VisualComponentsLib/MyListBox.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 VisualComponentsLib.CustomListBox
{
    [DefaultEvent(nameof(TextChanged))]
    public partial class MyListBox : UserControl
    {
        [Browsable(true)]
        public string selectedString
        {
            get => listBox.SelectedItem.ToString();
            set => listBox.SelectedItem = value;
        }

        public MyListBox()
        {
            InitializeComponent();
        }

        [Browsable(true)]
        public new event EventHandler? TextChanged
        {
            add => listBox.Items.Add(value);
            remove => listBox.Items.Clear();
        }

        private void ButtonAdd_Click(object sender, EventArgs e)
        {
            if (!string.IsNullOrEmpty(textBox.Text))
            {
                listBox.Items.Add(textBox.Text);

                textBox.Text = string.Empty;
            }
        }

        private void ButtonRemove_Click(object sender, EventArgs e)
        {
            listBox.Items.Clear();
        }
    }
}