Code Quality Rank: L2
Programming language: C#
License: MIT License
Latest version: v5.0.0

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Reactive Extensions

Channel Rx Ix
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  • NuGet v3 feed url (VS 2015+): https://pkgs.dev.azure.com/dotnet/Rx.NET/_packaging/RxNet/nuget/v3/index.json

System.Linq.Async / System.Interactive.Async / System.Interactive

v4.0 changes

Ix Async 4.0 has a breaking change from prior versions due to being the first LINQ implementation to support the new C# 8 async streams feature. This means for .NET Standard 2.1 and .NET Core 3 targets, we use the in-box interfaces for IAsyncEnumerable<T> and friends. On other platforms, we provide the implementation, so you can use await foreach and create async iterators as you would expect. The types will unify to the system ones where the platform provides it.

There are many breaking changes here; a full set of changenotes is on the way.


v5.0 changes

Rx.NET v5 is required for .NET 5 support of CSWinRT; earlier versions of Rx won't work correctly. To get the Windows API, you need to use the latest Windows SDK (19041), though you can target earlier versions of Windows.

Breaking changes In Windows, since the net5.0-windows10.0.19041 target now supports all Windows desktop object models, on UWP DispatcherObservable and releated SubscribeOn/ObserveOn were renamed to be CoreDispatcherObservable, SubscribeOnCoreDispatcher, and ObserveOnCoreDispatcher. This reflects the OS type names. Dispatcher refers only to the WPF type.

Supported Platforms

Rx 5.x supports the following platforms

  • .NET 5
  • .NET 5 with the Windows 10 19041 SDK (able to target earlier Windows versions)
  • .NET Framework 4.7
  • UWP 10.0.16299
  • .NET Standard 2.0

Support for UWP 10.0 has been removed.

v4.0 changes

Due to the overwhelming pain that fixing #205 - Implement assembly version strategy caused, we have refactored the libraries into a single library System.Reactive. To prevent breaking existing code that references the v3 libraries, we have facades with TypeForwarders to the new assembly. If you have a reference to a binary built against v3.0, then use the new System.Reactive.Compatibility package.

Supported Platforms

Rx 4.1 supports the following platforms

  • .NET Framework 4.6+
  • .NET Standard 2.0+ (including .NET Core, Xamarin and others)
  • UWP

Notably, Windows 8, Windows Phone 8 and legacy PCL libraries are no longer supported.

v3.0 breaking changes

The NuGet packages have changed their package naming in the move from v2.x.x to v3.0.0

This brings the NuGet package naming in line with NuGet guidelines and also the dominant namespace in each package. The strong name key has also changed, which is considered a breaking change. However, there are no expected API changes, therefore, once you make the NuGet change, no code changes should be necessary.

A Brief Intro

The Reactive Extensions (Rx) is a library for composing asynchronous and event-based programs using observable sequences and LINQ-style query operators. Using Rx, developers represent asynchronous data streams with Observables, query asynchronous data streams using LINQ operators, and parameterize the concurrency in the asynchronous data streams using Schedulers. Simply put, Rx = Observables + LINQ + Schedulers.

Whether you are authoring a traditional desktop or web-based application, you have to deal with asynchronous and event-based programming from time to time. Desktop applications have I/O operations and computationally expensive tasks that might take a long time to complete and potentially block other active threads. Furthermore, handling exceptions, cancellation, and synchronization is difficult and error-prone.

Using Rx, you can represent multiple asynchronous data streams (that come from diverse sources, e.g., stock quote, tweets, computer events, web service requests, etc.), and subscribe to the event stream using the IObserver<T> interface. The IObservable<T> interface notifies the subscribed IObserver<T> interface whenever an event occurs.

Because observable sequences are data streams, you can query them using standard LINQ query operators implemented by the Observable extension methods. Thus you can filter, project, aggregate, compose and perform time-based operations on multiple events easily by using these standard LINQ operators. In addition, there are a number of other reactive stream specific operators that allow powerful queries to be written. Cancellation, exceptions, and synchronization are also handled gracefully by using the extension methods provided by Rx.

Rx complements and interoperates smoothly with both synchronous data streams (IEnumerable<T>) and single-value asynchronous computations (Task<T>) as the following diagram shows:

Single return valueMultiple return values Pull/Synchronous/Interactive T IEnumerable<T> Push/Asynchronous/Reactive Task<T> IObservable<T>

Additional documentation, video, tutorials and HOL are available on MSDN, on Introduction to Rx, ReactiveX, and ReactiveUI.

Flavors of Rx

  • Rx.NET: (this repository) The Reactive Extensions (Rx) is a library for composing asynchronous and event-based programs using observable sequences and LINQ-style query operators.
  • RxJS: The Reactive Extensions for JavaScript (RxJS) is a library for composing asynchronous and event-based programs using observable sequences and LINQ-style query operators in JavaScript which can target both the browser and Node.js.
  • RxJava: Reactive Extensions for the JVM – a library for composing asynchronous and event-based programs using observable sequences for the Java VM.
  • RxScala: Reactive Extensions for Scala – a library for composing asynchronous and event-based programs using observable sequences
  • RxCpp: The Reactive Extensions for Native (RxCpp) is a library for composing asynchronous and event-based programs using observable sequences and LINQ-style query operators in both C and C++.
  • Rx.rb: A prototype implementation of Reactive Extensions for Ruby (Rx.rb).
  • RxPy: The Reactive Extensions for Python 3 (Rx.Py) is a set of libraries to compose asynchronous and event-based programs using observable collections and LINQ-style query operators in Python 3.

Interactive Extensions

  • Ix.NET: (included in this repository) The Interactive Extensions (Ix) is a .NET library which extends LINQ to Objects to provide many of the operators available in Rx but targeted for IEnumerable.
  • IxJS: An implementation of LINQ to Objects and the Interactive Extensions (Ix) in JavaScript.
  • IxCpp: An implementation of LINQ for Native Developers in C++


  • Tx: a set of code samples showing how to use LINQ to events, such as real-time standing queries and queries on past history from trace and log files, which targets ETW, Windows Event Logs and SQL Server Extended Events.
  • LINQ2Charts: an example for Rx bindings. Similar to existing APIs like LINQ to XML, it allows developers to use LINQ to create/change/update charts in an easy way and avoid having to deal with XML or other underneath data structures. We would love to see more Rx bindings like this one.


Source code


Some of the best ways to contribute are to try things out, file bugs, and join in design conversations.

Looking for something to work on? The list of up for grabs issues is a great place to start.

This project has adopted a code of conduct adapted from the Contributor Covenant to clarify expected behavior in our community. This code of conduct has been adopted by many other projects. For more information see the Code of conduct.

.NET Foundation

System.Reactive is part of the .NET Foundation. Other projects that are associated with the foundation include the Microsoft .NET Compiler Platform ("Roslyn") as well as the Microsoft ASP.NET family of projects, Microsoft .NET Core & Xamarin Forms.

Core Team

Geoffrey Huntley Sydney, Australia Claire Novotny New York, USA David Karnok Budapest, Hungary Daniel C. Weber Aachen, Germany