C# 4 and .NET 4

1102 ❘ ChaPTer 38 silverliGht
neTWorKing
With Silverlight, networking is in some ways the same as from the .NET Framework stack, but it is also
different in important aspects. You have the socket classes HttpRequest and WebClient that you are
familiar with from Chapter 24. WCF (Chapter 43) and WCF Data Services (Chapter 32) are available as
well. However, only asynchronous methods are available to send and receive requests to and from the
network. The UI thread shouldn ’ t be blocked, as this can have a fatal effect for the user.
Before Silverlight 3.0, the only networking stack that could be used from Silverlight was the one that was
offered by the browser. Since Silverlight 3.0, this is different; you can use a different HTTP stack as well.
One important restriction for applications running inside a browser on the client was that the client
could only access networking services from the same server that the control came from. This has changed
since Adobe ’ s Flash technology, but the target server must support this. The Silverlight networking stack
checks to see if a Silverlight Policy File named clientaccesspolicy.xml exists on the server. If such
a fi le does not exist, Silverlight also accepts the fi le crossdomain.xml , which is the same fi le used with
Adobe Flash. The second fi le is not checked if the fi rst exists, and Silverlight doesn ’ t use all entries from the
crossdomain.xml fi le and requires that the entire domain be marked as public if this fi le is used.
A sample Silverlight Policy File, clientaccesspolicy.xml , is shown here. For the client domain
www.cninnovation.com , access is granted to all subpaths. You can restrict the resources that the grant
applies to, and also use an * for the domain URI to allow clients to come from anywhere.
< xml version="1.0" encoding="utf - 8" >
< access - policy >
< cross - domain - access >
< policy >
< allow - from http - request - headers="*" >
< domain uri="http://www.cninnovation.com"/ >
< /allow - from >
< grant - to >
< resource path="/" include - subpaths="true"/ >
< /grant - to >
< /policy >
< /cross - domain - access >
< /access - policy >
Let ’ s look at an example that uses networking stacks from
Silverlight. For this, an ADO.NET Entity Data Model is
created fi rst, to read and write to and from a database
across the network.
Creating an ado.neT entity data model
The sample Silverlight control is used to write attendee
registration information to a database. First, the user must
select from a list of events before he can register for an event.
The database EventRegistration defi nes three tables:
Events, Attendees, and RegistrationCodes, which are mapped
to the ADO.NET Entity Data Model entity classes Event ,
Attendee , and RegistrationCode , as shown in Figure 38 - 4.
figure 38-4
You can read about how to create and use ADO.NET Entity Data Models in
Chapter 31, “ADO.NET Entity Framework.”
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