/// <summary>
        /// Adds new tab item to the Tabs collection.
        /// </summary>
        public void AddItem(TabViewModel sender)
        {
            TabViewModel newTabItem = new TabViewModel(this);

            newTabItem.Header     = "New Tab";
            newTabItem.IsSelected = true;
            if (sender != null)
            {
                int insertIndex = this.Tabs.IndexOf(sender) + 1;
                this.Tabs.Insert(insertIndex, newTabItem);
            }
            else
            {
                this.Tabs.Add(newTabItem);
            }
        }
 /// <summary>
 /// Removes an item from the Tabs collection.
 /// </summary>
 /// <param name="tabItem">The tab item.</param>
 public void RemoveItem(TabViewModel tabItem)
 {
     this.Tabs.Remove(tabItem);
     tabItem.Dispose();
 }