Feeds

Silverlight 2.0 data and web services explained

Mashups and large downloads challenge

Build a business case: developing custom apps

Mix 08 Microsoft Silverlight team member Eugene Osovetsky has explained to a packed Mix 08 session how Silverlight 2.0, released as beta on Wednesday, interacts with external data and web services.

No surprise: the first thing we saw was based on the Windows Communication Foundation (WCF), Microsoft's universal .NET web services API.

Presuming you use ASP.NET and Visual Studio, this involves creating a WCF service by marking up .NET code with attributes such as ServiceContract and DataContract, then consuming the service in a Silverlight application by adding a Service Reference and coding against it. Silverlight requires AJAX-style asynchronous calls to a proxy class, with the results processed in a callback event handler. Silverlight has rich bindable data controls including a listbox and a datagrid.

That's all well and good, but not everyone wants or can use end-to-end .NET. Fortunately Silverlight also supports standard SOAP by importing a WSDL, or generic web services using XML or JSON, though a little more code is needed. Once again, the Silverlight code involves asynchronous calls, this time using a generic WebClient class that will already be familiar to .NET programmers.

There are complications with REST, though. The problem is that Silverlight, like Adobe Systems' Flash, does not have its own networking stack but relies on the browser's plug-in API. This gets you benefits like sharing the browser's authenticated connections, but also brings limitations.

Apparently it is simply not possible to use HTTP PUT or DELETE methods, a problem that leads to hacks like HTTP POSTs that delete data, breaking the HTTP specification. This is not the fault of Silverlight, but it is unfortunate. For similar reasons, there is no access to SOAP fault messages.

There is also a big issue with cross-domain data sources, which poses a problem for mash ups. Cross-domain access is prevented by default for security reasons. Otherwise, a bad Silverlight application might hijack an existing authenticated connection to some other site.

Cross-domain data is the essence of mash ups, though. The solution with Silverlight is that services can opt in to being called cross domain by including a policy file. Silverlight has its own, or will observe a Flash policy file. Therefore, public services that work with Flash should also work with Silverlight. Cross-domain access over SSL is promised, but not supported in the current beta.

Osovetsky remarked that Silverlight 2.0 has moved away from JSON towards SOAP, saying that JSON has little advantage if the client code is not JavaScript, though he admitted that JSON has a smaller message size. Microsoft is investigating binary XML for Silverlight, but it seems unlikely this will make the first release.

This puts Silverlight at a disadvantage to Flash for downloading large amounts of data, since Flash can use Adobe's efficient ActionScript Message Format. In mitigation, Silverlight is inherently flexible and there is plenty of scope for custom solutions.®

Boost IT visibility and business value

More from The Register

next story
KDE releases ice-cream coloured Plasma 5 just in time for summer
Melty but refreshing - popular rival to Mint's Cinnamon's still a work in progress
Leaked Windows Phone 8.1 Update specs tease details of Nokia's next mobes
New screen sizes, dual SIMs, voice over LTE, and more
PEAK LANDFILL: Why tablet gloom is good news for Windows users
Sinofsky's hybrid strategy looks dafter than ever
Fiendishly complex password app extension ships for iOS 8
Just slip it in, won't hurt a bit, 1Password makers urge devs
Mozilla keeps its Beard, hopes anti-gay marriage troubles are now over
Plenty on new CEO's todo list – starting with Firefox's slipping grasp
Apple: We'll unleash OS X Yosemite beta on the MASSES on 24 July
Starting today, regular fanbois will be guinea pigs, it tells Reg
Another day, another Firefox: Version 31 is upon us ALREADY
Web devs, Mozilla really wants you to like this one
prev story

Whitepapers

Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Why and how to choose the right cloud vendor
The benefits of cloud-based storage in your processes. Eliminate onsite, disk-based backup and archiving in favor of cloud-based data protection.
The Essential Guide to IT Transformation
ServiceNow discusses three IT transformations that can help CIO's automate IT services to transform IT and the enterprise.
Maximize storage efficiency across the enterprise
The HP StoreOnce backup solution offers highly flexible, centrally managed, and highly efficient data protection for any enterprise.