Invoking on the GUI Thread

As explained in the previous section, the notification is received by a background thread and not by the GUI thread on which the application is running. Although the refresh method cannot be run directly it can be invoked using a delegate.

1. In the MainWindow.xaml.cs code file, define a delegate type for refreshing the display that takes no parameters called RefreshDelegate and declare a member of this type.

   public partial class MainWindow: Window
   {
       private JoobContext context;
       private Bank bank;
       delegate void RefreshDelegate();
       RefreshDelegate refreshDelegate;

2. In the form constructor, point the refreshDelegate member to the refresh method.

   public MainWindow()
   {
       InitializeComponent();
       context = new JoobContext();
       bank = context.FirstInstance<Bank>();
       context.RegisterClassNotificationHandler(typeof(Customer), 
                                          NotificationEventConstants.SystemCreate, 
                                          customerCreatedNoteHandler);
       refreshDelegate = new RefreshDelegate(refresh);

3. In the customerCreatedNoteHandler notification event handler method, use the Invoke method to marshal the refresh method to the GUI thread.

   private void customerCreatedNoteHandler(object sender, NotificationEventArgs e)
   {
       MessageBox.Show("Customer added");
       Dispatcher.Invoke(refreshDelegate);
   }

4. Run the BankingApp application and then enter data for a new customer. Click the Add button to add the customer. After the message box is closed, the list of customers is refreshed automatically.