MSDN Magazine - September 2008 - (Page 30)

Figure 6 ListBox XAML the values in rows and columns (the ListBox was initially shown in Figure 1). By setting the ItemSource property of the ListBox, we indicate that the ListBox will get its values from a bound data source as shown by the following markup: push its values to the target (the ListBox and any items bound within it) both on initial load and when anything changes in the source (see the Binding Modes section for more details on Modes). Asynchronous Communication Notice that the ItemSource property simply indicates that it will be bound, but not to any specific object or property. Since no source is specified, the ListBox will refer to any inherited DataContext object sources in the XAML. The DataContext can be inherited from The binding Mode property determines the frequency and direction of binding. any parent FrameworkElement. The sample application sets the DataContext of the ListBox named lbProducts in the codebehind after the WCF service has returned the list of products: lbProducts.DataContext = productList; Before the binding can occur, the product list must be fetched from the WCF service. All WCF service calls from Silverlight are made through asynchronous communications. The sample WCF service publishes an OperationContract named FindProductList. Since the communication with Silverlight is asynchronous, this contract is implemented in the generated proxy with an asynchronous method that kicks off the communication and an event that is raised when the operation has completed. The following code creates an instance of the service proxy: private void FindProductList() { this.Cursor = Cursors.Wait; var proxy = new NWServiceGatewayClient(); proxy.FindProductListCompleted += new EventHandler ( FindProductListCompleted); proxy.FindProductListAsync(); } Once this code has been executed, the ListBox is bound to the list of products and each ListBoxItem in the DataTemplate is bound to an individual product in the list. Figure 6 shows the XAML used to create the ListBox and bind the items represented in the DataTemplate to the source. Notice that the individual controls that are bound to the source use the binding markup extensions to indicate which property of the Product they will be bound to, as well as to use the OneWay binding mode. For example: Text="{Binding ProductName, Mode=OneWay}" After the proxy has been created, an event handler is added to the FindProductListCompleted event. This is the method that will receive the result of the asynchronous WCF service call. Finally, the FindProductListAsync method is executed. When the asynchronous WCF service call has completed, the event handler is executed. The following code shows the event handler FindProductListCompleted receiving the list of products and binding them to the ListBox’s DataContext: private void FindProductListCompleted(object sender, FindProductListCompletedEventArgs e) { ObservableCollection productList = e.Result; lbProducts.DataContext = productList; if (lbProducts.Items.Count > 0) lbProducts.SelectedIndex = 0; this.Cursor = Cursors.Arrow; } The binding mode for all of the bound TextBox controls is set to OneWay. This indicates that the source (the Product instance) should 30 msdn magazine Data Points

Table of Contents Feed for the Digital Edition of MSDN Magazine - September 2008

MSDN Magazine - September 2008 Contents Toolbox CLR Inside Out Data Points Advanced Basics Office Space Cutting Edge Hierarchy ID New Features for Microsoft SQL Server 2008 Prism Data Services Advanced WPF Test Run Security Briefs Foundations { End Bracket }

MSDN Magazine - September 2008

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