C#

OuterPanel.HorizontalScroll.Value = e.NewValue;

ListBox1.Items[0]-->"City One"    ---------------- ListBox2.Items[0]=2500
ListBox1.Items[1]->"City Two"    ---------------- ListBox2.Items[1]=3000
ListBox1.Items[2]-->"City Three"  ---------------- ListBox2.Items[2]=1500

ListBox1.Items[0]->"City Two"    <----------------> ListBox2.Items[0]=3000
ListBox1.Items[1]-->"City One"   <----------------> ListBox2.Items[1]=2500
ListBox1.Items[2]-->"City Three" <----------------> ListBox2.Items[2]=1500

ListBox2.Items[0]=2500
ListBox2.Items[1]=3000
ListBox2.Items[2]=1500

ListBox1.Items[0]-->"City One"
ListBox1.Items[1]->"City Two"
ListBox1.Items[2]-->"City Three"

City One =2500
City Two=3000
City Three=1500

ListBox2.Sorted = true;

private Dictionary<string, int> PopCityDict;

private void Form1_Load(object sender, EventArgs e)
{
    PopCityDict = new Dictionary<string, int>
    {
        {"City One", 2500},
        {"City Two", 3000},
        {"City Three", 1500}
    };

    InitializeListBoxes();
}

private void InitializeListBoxes()
{
    listBox1.Items.Clear();
    listBox2.Items.Clear();

    foreach (var kvp in PopCityDict)
    {
        listBox1.Items.Add(kvp.Key);
        listBox2.Items.Add(kvp.Value);
    }
}

private void SortDescendingButton_Click(object sender, EventArgs e)
{
    listBox1.Items.Clear();
    listBox2.Items.Clear();

    foreach (var kvp in PopCityDict.OrderByDescending(criterion => criterion.Value))
    {
        listBox1.Items.Add(kvp.Key);
        listBox2.Items.Add(kvp.Value);
    }
}

InitializeListBoxes();

public class City
{
    public const int MinPopulation = 0;

    public event EventHandler PopulationChanged;

    private string name;
    private int population;

    public City(string name, int population)
    {
        if (string.IsNullOrEmpty(name))
            throw new ArgumentNullException("name", "Name cannot be null or empty");
        // Do more validation here for only whitespace etc

        if (population < MinPopulation)
            throw new ArgumentOutOfRangeException(
                "population",
                string.Format("Population cannot be less than {0}", MinPopulation));
        this.name = name;
        this.population = population;
    }

    public string Name
    {
        get { return name; }
    }
    public int Population
    {
        get { return population; }
        set
        {
            if (value < MinPopulation)
                throw new ArgumentOutOfRangeException(
                    "Population",
                    string.Format("Population cannot be less than {0}", MinPopulation));
            population = value;
            OnPopulationChanged(EventArgs.Empty);
        }
    }

    protected virtual void OnPopulationChanged(EventArgs e)
    {
        EventHandler eh = PopulationChanged;
        if (eh != null)
            eh(this, e);
    }
    public static int CompareName(City first, City second)
    {
        if (object.ReferenceEquals(first, second)) // same reference or both null
            return 0;
        if (object.ReferenceEquals(first, null)) // first null?
            return -1;
        if (object.ReferenceEquals(second, null)) // second null?
            return 1;
        return first.name.CompareTo(second.name); // neither null and different reference so compare
    }
    public static int ComparePopulation(City first, City second)
    {
        if (object.ReferenceEquals(first, second)) // same reference or both null
            return 0;
        if (object.ReferenceEquals(first, null)) // first null?
            return -1;
        if (object.ReferenceEquals(second, null)) // second null?
            return 1;
        return first.population.CompareTo(second.population); // neither null and different reference so compare
    }
}

using System;
using System.Collections.Generic;
using System.Windows.Forms;

public partial class FormMain : Form
{
    private const string SortByNameText = "&Sort by Name";
    private const string SortByPopulationText = "&Sort by Population";

    private List<City> cities;

    public FormMain()
    {
        InitializeComponent();
        cities = new List<City>();
        BuildCityList();
        listBox1.DataSource = cities;
        listBox1.DisplayMember = ("Name");
        listBox2.DataSource = cities;
        listBox2.DisplayMember = ("Population");
        buttonSort.Text = "&Sort by Name";
        buttonSort.Click += new EventHandler(buttonSort_Click);
    }

    void buttonSort_Click(object sender, EventArgs e)
    {
        if (buttonSort.Text == SortByNameText)
        {
            cities.Sort(new Comparison<City>(City.CompareName));
            buttonSort.Text = SortByPopulationText;
        }
        else
        {
            cities.Sort(new Comparison<City>(City.ComparePopulation));
            buttonSort.Text = SortByNameText;
        }
        listBox1.DataSource = null;
        listBox2.DataSource = null;
        listBox1.DataSource = cities;
        listBox1.DisplayMember = ("Name");
        listBox2.DataSource = cities;
        listBox2.DisplayMember = ("Population");
    }

    private void BuildCityList()
    {
        cities.Add(new City("City One", 2500));
        cities.Add(new City("City Two", 3000));
        cities.Add(new City("City Three", 1500));
    }
}

Thread.CurrentThread.Resume();