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This article mainly explains "how to consume WCF services in Silverlight3". The content of the explanation is simple and clear, and it is easy to learn and understand. Please follow the editor's ideas to study and learn "how to consume WCF services in Silverlight3".

Consumption of service

VS2008's Silverlight tool provides built-in functionality to create WCF services activated with Silverlight and consume WCF services without writing a lot of code. Silverlight 3 now supports binary XML, which can transfer data from the server to the client faster. Standard SOAP messages can also be transmitted if necessary.

If you have consumed an ASP.NET ASMX Web service before, you will find it easy to consume WCF services. VS2008's new service reference dialog box allows you to select the service and generate the client without writing a lot of code. Before generating the proxy, understand that Silverlight can only be called back to the original server, where the Silverlight XAP application file is provided by default.

If you need to invoke a WCF service, which may exist in different domains or different ports, the service must have a customer access policy file named clientaccesspolicy.xml, which is located at the low end of the server. Silverlight checks the file to see if it is allowed to make cross-domain calls.

Example 1 below shows a sample file:

< ?xml version="1.0" encoding="utf-8"?>

< access-policy>

< cross-domain-access>

< policy>

< allow-from>

< domain uri="*"/>

< /allow-from>

< grant-to>

< resource path="/" include-subpaths="true"/>

< /grant-to>

< /policy>

< /cross-domain-access>

< /access-policy>

Example 1: customer access policy files can be placed at the low end of the server to allow Silverlight clients to invoke services in different domains or running on different ports.

To create a WCF service proxy, you first need to create a Silverlight application project. Once the project has been created, you can right-click the project and select add Service reference. As shown below, the system provides an Add Service Reference dialog box, and figure 1 shows that the Add Service Reference dialog box can quickly and easily generate customer agents without a large amount of code.

Figure 1:

If the WCF service is in the same VS scheme, you can click the Discover button. Otherwise, you will have to enter the path to the Web Service Description Language (WSDL) file in the Address text box. Once the file is located, you can give the agent code a namespace and click the confirm button.

Once the client agent is created, you can invoke the service in the Silverlight application. Keep in mind that all network operations that occur with Silverlight are asynchronous, so the browser does not lock up when the service is invoked.

Example 2 shows an example of invoking services and binding data using client code:

Void MainPage_Loaded (object sender, RoutedEventArgs e) {/ / Create service proxy WcfService.Service1Client proxy = new WcfService.Service1Client (); / / Wire the proxy to a completed handler to allow the async operation to be handled proxy.GetCustomerCompleted + = new EventHandler

< WcfService.GetCustomerCompletedEventArgs>

(proxy_GetCustomerCompleted); / / Call the service asynchronously proxy.GetCustomerAsync (id);} void proxy_GetCustomerCompleted (object sender, SilverlightApplication1.WcfService.GetCustomerCompletedEventArgs e) {/ / Bind the returned data to the DataContext this.DataContext = e.Result;}

Example 2: use a client proxy object to invoke the WCF service in Silverlight.

Looking at the code in example 2, you can see that the proxy object is created and then bundled by an asynchronous event handler called proxy_GetCustomerCompleted through an event-driven pattern. The service is invoked asynchronously by invoking the GetCustomerAsync method. Once the service returns data, the recall method is automatically invoked and the GetCustomerCompletedEventArgs parameter is accessed to retrieve the data. In this example, the data is directly bound to the DataContext property of the application. Note that no additional operations are required to set the data delivery route. The agent will take care of everything automatically.

Silverlight applications cannot call a database directly, but they can access data from a range of services such as WCF services, ASMX services, and other standards-compliant services.

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