Выпадающий список с сheckbox'ами

public partial class CheckComboBox : ComboBox
    {
        /// <summary>
        /// C'tor
        /// </summary>
        public CheckComboBox()
        {
            this.DrawMode = DrawMode.OwnerDrawFixed;
            this.DrawItem += new DrawItemEventHandler(CheckComboBox_DrawItem);
            this.SelectedIndexChanged += new EventHandler( CheckComboBox_SelectedIndexChanged );
            SelectedText = "Select Options";
        }
 
        /// <summary>
        /// Invoked when the selected index is changed on the dropdown.  This sets the check state
        /// of the CheckComboBoxItem and fires the public event CheckStateChanged using the 
        /// CheckComboBoxItem as the event sender.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void CheckComboBox_SelectedIndexChanged( object sender, EventArgs e )
        {
            CheckComboBoxItem item = (CheckComboBoxItem)SelectedItem;
            item.CheckState = !item.CheckState;
            if (CheckStateChanged != null)
                CheckStateChanged(item, e);
        }
 
        /// <summary>
        /// Invoked when the ComboBox has to render the drop-down items.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void CheckComboBox_DrawItem( object sender, DrawItemEventArgs e )
        {
            // make sure the index is valid (sanity check)
            if( e.Index == -1 )
            {
                return;
            }
 
            // test the item to see if its a CheckComboBoxItem
            if( !( Items[ e.Index ] is CheckComboBoxItem ) )
            {
                // it's not, so just render it as a default string
                e.Graphics.DrawString(
                    Items[ e.Index ].ToString(),
                    this.Font,
                    Brushes.Black,
                    new Point( e.Bounds.X, e.Bounds.Y ) );
                return;
            }
 
            // get the CheckComboBoxItem from the collection
            CheckComboBoxItem box = (CheckComboBoxItem)Items[ e.Index ];
 
            // render it
            CheckBoxRenderer.RenderMatchingApplicationState = true;
            CheckBoxRenderer.DrawCheckBox(
                e.Graphics,
                new Point( e.Bounds.X, e.Bounds.Y ),
                e.Bounds,
                box.Text,
                this.Font,
                ( e.State & DrawItemState.Focus ) == 0,
                box.CheckState ? CheckBoxState.CheckedNormal : CheckBoxState.UncheckedNormal );
        }
 
        /// <summary>
        /// Fired when the user clicks a check box item in the drop-down list
        /// </summary>
        public event EventHandler CheckStateChanged;
 
    }