MSDN Magazine - November 2008 - (Page 34)

The method accepts two parameters, as you see here: public virtual object Invoke(string name, params object[] args) 6\QFKURQRXV&DOOVDQG6LOYHUOLJKW Silverlight 2 supplies a variety of APIs to make calls to remote endpoints, but all of them must be asynchronous. You can start the call on a background thread, but you can’t force the UI thread to sync up. If you block the UI thread on a sync object, you actually stop the UI thread indefinitely, and no command that resets the sync object can ever resume it. There’s a big debate in the community about synchronous calls in Silverlight. Nonetheless, synchronous calls from within the Silverlight API to a remote endpoint are simply not supported today because they are known and proven to have associated latency. Synchronous calls are an important feature in the browser environment, however. They’re supported in all browsers that support XmlHttpRequest. XmlHttpRequest is a browser object that enables AJAX scenarios. The object leverages the browser machinery to make a call to an endpoint within the same domain. By default, XmlHttpRequest operates asynchronously, and this is the way in which most AJAX frameworks use it. However, XmlHttpRequest can be quite easily configured to operate synchronously. By creating and controlling an instance of XmlHttpRequest from Silverlight, you can arrange synchronous calls and fix all those particular scenarios where a synchronous call would make coding much easier. (Personally, I’m not a big fan of the async-only nature of Silverlight remote calls. Async calls are sufficient most of the time, but I think that, especially when you’re adapting some The first argument indicates the name of the method to invoke on the scriptable object stored in the current instance of ScriptObject. The second argument is simply the list of arguments for the method to invoke. The method is responsible for correctly marshaling types across the two different runtime environments. On the way to the browser, it transforms managed objects into JavaScript-compatible types; on the way back, it does the reverse. There’s another method on HtmlWindow that deserves some attention here—the CreateInstance method: public ScriptObject CreateInstance( string typeName, params object[] args) The method allows you to create an instance of the specified JavaScript object. The type name parameter indicates the name of the JavaScript object to instantiate. Internally, the method prepares a dynamic JavaScript function that creates the specified object and then invokes the function from Silverlight: ScriptObject xhr = HtmlPage.Window.CreateInstance("XMLHttpRequest"); The method CreateInstance is useful for obtaining a scriptable reference to a JavaScript object. Next, you script it using the Invoke method. These features are incredibly helpful when you really need to make synchronous calls from Silverlight 2. The problem is that synchronous calls are not permitted in Silverlight 2. 34 msdn magazine Cutting Edge http://www.datadynamics.com

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

Contents MSDN Magazine - November 2008 Toolbox CLR Inside Out Data Points Cutting Edge Security Briefs Test Your Security IQ Agile SDL Access Control Utility Spotlight RIA Test Run Wicked Code Foundations Team System End Bracket

MSDN Magazine - November 2008

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