ItemChangedEventArgs 这个类中包含一个Index属性,MSDN中是这么叙述的"更改项的从零开始的索引。"但是在实际代码中我看到有一个判断是 if (index == -1),如:

void OnManagerItemChanged(object sender, ItemChangedEventArgs e)

        {

                if (e.Index == -1)

                {

                    this.ContextMenu = myContextMenu;

                    this.ContextMenu.MenuItems.Clear();

                    foreach (object s in manager.List)

                    {

                        PropertyDescriptor pd = this.manager.GetItemProperties()[this.dataMember];

                        if (pd != null)

                        {

                            this.ContextMenu.MenuItems.Add(Convert.ToString(pd.GetValue(s)), new EventHandler(MyMenuClicked));

                        }

                    }

                }

这里的Index等于-1指的是什么意思?