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.

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;

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);

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);
}

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.