private void AddNewBookButton_Click(object sender, RoutedEventArgs e)
        {
            var window = new DialogVM(null);
            var dialog = new Dialog()
            {
                Title       = "New Book",
                DataContext = window
            };

            if (dialog.ShowDialog() ?? false)
            {
                items.Add(window.Result);
            }
        }
 private void ShowEditDialog()
 {
     if (BookList.SelectedItems.Count == 1)
     {
         if (BookList.SelectedItem is Book book)
         {
             DialogVM model  = new DialogVM(book);
             Dialog   dialog = new Dialog()
             {
                 Title       = "Edit Book",
                 DataContext = model
             };
             dialog.ShowDialog();
         }
     }
     else if (BookList.SelectedItems.Count == 0)
     {
         MessageBox.Show("Select an item to edit.", "Warning");
     }
     else
     {
         MessageBox.Show("Select only one item to edit.", "Warning");
     }
 }