/// <summary>
        /// Populate and show the listbox
        /// </summary>
        public virtual void ShowListBox()
        {
            OnDropDownOpen(EventArgs.Empty);

              using (ListBox l_ListBox = new ListBox())
              {
            l_ListBox.BorderStyle = BorderStyle.None;
            l_ListBox.HorizontalScrollbar = true;
            l_ListBox.IntegralHeight = false;
            if (Validator.StandardValues != null)
            {
              foreach (object o in Validator.StandardValues)
              {
            l_ListBox.Items.Add(Validator.ValueToDisplayString(o));
              }
            }

            // Calculate the height of the ListBox : l_ListBox.Height
            int defaultHeight = l_ListBox.ItemHeight * 3;
            int maximumHeight = (int)(Screen.PrimaryScreen.Bounds.Height / 2.1);
            l_ListBox.Height = Math.Max(defaultHeight, Math.Min(maximumHeight, l_ListBox.PreferredHeight)) + 2;

            using (DropDownCustom l_DropDown = new DropDownCustom(this, l_ListBox))
            {
              if (selectedItem >= 0 && selectedItem < l_ListBox.Items.Count)
              {
            l_ListBox.SelectedIndex = selectedItem;
              }
              l_ListBox.SelectedIndexChanged += new EventHandler(ListBox_SelectedChange);
              l_ListBox.Click += new EventHandler(ListBox_Click);
              l_DropDown.ShowDropDown();
              l_ListBox.Click -= new EventHandler(ListBox_Click);
              l_ListBox.SelectedIndexChanged -= new EventHandler(ListBox_SelectedChange);

              txtBox.Focus();

              OnDropDownClosed(EventArgs.Empty);
            }
              }
        }
 /// <summary>
 /// Displays the specified control in a drop down area below a value field of the property grid that provides this service.
 /// </summary>
 /// <param name="control">The drop down list <see cref="T:System.Windows.Forms.Control"></see> to open.</param>
 public virtual void DropDownControl(System.Windows.Forms.Control control)
 {
     this.dropDown = new DropDownCustom(this, control);
       this.dropDown.DropDownBehaviours = DropDownBehaviours.CloseOnEscape;
       this.dropDown.ShowDropDown();
       this.dropDown = null;
 }