PraktikaGlava4/Form3.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 Praktika409
{
    public partial class Form3 : Form
    {
        public Form3()
        {
            InitializeComponent();
            comboBox1.SelectedIndexChanged += comboBox1_SelectedIndexChanged;

            List<Phone> phones = new List<Phone>
        {
            new Phone { Id=11, Name="Samsung Galaxy Ace 2", Year=2012},
            new Phone { Id=12, Name="Samsung Galaxy S4", Year=2013},
            new Phone { Id=13, Name="iPhone 6", Year=2014},
            new Phone { Id=14, Name="Microsoft Lumia 435", Year=2015},
            new Phone { Id=15, Name="Xiaomi Mi 5", Year=2015}
        };

            listBox1.DataSource = phones;
            listBox1.DisplayMember = "Name";
            listBox1.ValueMember = "Id";

            listBox1.SelectedIndexChanged += listBox1_SelectedIndexChanged;

        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            string selectedState = comboBox1.SelectedItem.ToString();
            MessageBox.Show(selectedState);
        }

        private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            // получаем id выделенного объекта
          //  int id = (int)listBox1.SelectedValue;

            // получаем весь выделенный объект
          //Phone phone = (Phone)listBox1.SelectedItem;
        //  MessageBox.Show(id.ToString() + ". " + phone.Name);
        }

        private void comboBox4_SelectedIndexChanged(object sender, EventArgs e)
        {
            Phone phone = (Phone)comboBox1.SelectedItem;
            listBox1.Items.Add(phone);
        }
    }
    class Phone
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Year { get; set; }
    }
}