private void AddTabItemViewModel()
        {
            var vm = new DirectoryTabItemViewModel();

            DirectoryTabItems.Add(vm);

            CurrentDirectoryTabItem = vm;
        }
        private void CloseTab(DirectoryTabItemViewModel vm)
        {
            var isCurrent = CurrentDirectoryTabItem == vm;

            DirectoryTabItems.Remove(vm);
            if (isCurrent)
            {
                CurrentDirectoryTabItem = DirectoryTabItems.LastOrDefault();
            }
        }