C#: Change DropDownList value when Enter key is pressed

I have a windows form with a DropDownList with a fixed number of items. How do I make the DropDownList increment to the next item when I press Enter and whe开发者_如何学Cn it reaches the end of the items, return to the first item.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.KeyPreview = true;
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            this.comboBox1.DataSource = CreateItems();

        }


        private List<string> CreateItems()
        {
            List<string> lst = new List<string>();
            lst.Add("One");
            lst.Add("Two");
            lst.Add("Three");
            lst.Add("Four");
            return lst;
        }

        private void comboBox1_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyData == Keys.Enter)
            {
                if (comboBox1.SelectedIndex == comboBox1.Items.Count-1)
                {
                    comboBox1.SelectedIndex = 0;
                    return;
                }

                if (comboBox1.SelectedIndex >=0 & comboBox1.SelectedIndex< comboBox1.Items.Count-1)
                {

                    comboBox1.SelectedIndex = comboBox1.SelectedIndex+1;
                }

            }
        }

    }
}

You need to handle the KeyDown event and change the SelectedIndex property.