WPF ListBox Exception while using WCF

Hi.

I have a WCF service that retrieves information from a database. It does so as follows:

public List<string> ShowAllBooks()
        {
            List<string> booksList = new List<string>();
            try
            {

                using (bookcatalogueEntities context = new bookcatalogueEntities())
                {
                    // Fetch the product number of every product in the database
                    var books = from b in context.catalagues
                                   select b.Title;
                    booksList = books.ToList();
                }
            }
            catch
            {
                // Ignore exceptions in this implementation
            }
            // Return the list of product numbers
            return booksList;
        }
    }

When the WPF Client starts, the items (books) should be shown in a list box. I have this for the list box code behind:

private void ShowAllBooks()
        {
            CatalogueManagerClient.ServiceReference.BookCatalogueServiceClient proxy = new BookCatalogueServiceClient();
            try
            {



                lbBooks.Dispatcher.Invoke(new Action(() =>
                {

                    lbBooks.ItemsSource =  proxy.ShowAllBooks();
                }), DispatcherPriority.ApplicationIdle);
                //books = App.BookCatalogue.GetBook(query);
                //lbBooks.ItemsSource = books;
                txtBookPath.Foreground = Brushes.Black;
                txtBookPath.Text = "Ready";
            }
            catch (CommunicationException ex)
            {
                MessageBox.Show(proxy.State.ToString() + " ..."+ex.Message);

            }

        }

and for the xaml part, i have:

<ListBox Height="440"  KeyDown="lbBooks_KeyDown"  MouseDoubleClick="lbBooks_MouseDoubleClick"  Name="lbBooks" SelectionChanged="lbBooks_SelectionChanged"  Width="210" />

The problem is that when the client starts, it can show the books in the listbox. The problem is that when i select a book, it throws a run time error called:

InvalidOperationException

Stating:

Items collection must be empty before using ItemsSource.

I have tried googling for a solution and gone through articles and problems here but i cannot find a matching problem. Please assist on how to resolve this problem.

Tags: C# (C# 4.0)