public void RemoveSelection(ProjectViewModel projectViewModel)
 {
     if (_selectedItems.Remove(projectViewModel))
     {
         projectViewModel.NotifyIsSelectedChanged();
         NotifySelectionChanged();
     }
 }
        public void AddSelection(ProjectViewModel projectViewModel)
        {
            if (projectViewModel == null)
            {
                return;
            }

            if (_selectedItems.Add(projectViewModel))
            {
                projectViewModel.NotifyIsSelectedChanged();
                NotifySelectionChanged();
            }
        }