Preview of Reactive Extensions for .NET Available

Microsoft announced the availability of a Reactive Extensions for .NET (Rx) preview on Wednesday, in conjunction with its Professional Developers Conference 2009, held this week in Los Angeles.

Rx is a .NET Framework extension library that developers can use to build “reactive applications”—applications that can react to changes to the collections in their environment. In the past, this event-based behavior has typically been handled via locks and event handlers. With Rx, developers can write declarative code that leverage changes in the properties of observable collections to fire off push-based, asynchronous behavior in their applications.

Using the Task Parallel library for concurrency, Rx builds on LINQ standard sequence operators in the .NET Framework 4 and Silverlight 4 to enable push-based notifications. Other .NET entities can leverage these notifications, greatly simplifying the creation of asynchronous applications.

Any .NET-compliant language can use Rx, from the familiar Visual Basic and C# to newer languages like F#.

An example of Rx in use is the Silverlight Toolkit. Microsoft used Rx to build the Silverlight Toolkit Drag and Drop Framework, which uses the Windows Presentation Foundation (WPF) to create and react to drag-and-drop operations within a Silverlight application. Rx was also used by Microsoft in the Silverlight unit testing framework to write reliable, readable asynchronous test code. Rx drastically reduced development and testing time for the Silverlight team.

In addition to the observable collection library extensions, there are a number of experimental items included in this release of Rx. These include types and namespaces to extend Rx functionality to enumerable collections, as well as a .NET Framework 3.5 version of PLINQ.

The MSDN DevLabs site provides Rx preview downloads for .NET Framework 3.5 SP1, .NET Framework 4 Beta 2, and Silverlight 3. Both Visual Studio 2008 SP1 and Visual Studio 2010 Beta 2 are supported development environments.

About the Author

Terrence Dorsey is a technical writer, editor and content strategist specializing in technology and software development. Over the last 25-plus years he has worked on developer-focused projects at ESPN, The Code Project, and Microsoft. Read his blog at or follow @tpdorsey on Twitter.

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