Reactive.EventAggreator

This is an update of a blog post from José F. Romaniello about using Reactive Extensions to implement an event aggregator. source

Usage

To install it, just run this from the Package Manager Console:

Install-Package Reactive.EventAggregator

Why bring it back?

Three reasons:

• I wanted a simple event aggregator, without taking a dependency on an MVVM framework
• It should be available on NuGet
• Demonstrate Portable Class Libaries and targetting different platforms from one codebase

Portable Class Libraries All The Things (kinda)

I use this project as an excuse to investigate how to use PCL with NuGet, but hit some issues which made the experience less-than-appealing.

Yes, NuGet supports installing packages into PCL projects.

While the NuGet docs only mention two profiles, I've seen at least three different ones in the wild:

• portable-windows8+net45 - a small profile encompassing the modern APIs
• portable-sl4+wp71+windows8 - the biggest range of profiles, and thus the smallest set of available APIs
• portable-win+net40+sl50+wp8 - this is what the Autofac 3.0 beta supports

Why does this matter? Because if you try and install something from NuGet into a PCL project, you may see an error like this:

Could not install package 'Rx-Interfaces 2.0.21114'. You are trying to install this package into a project that targets 
'portable-win+net45+sl50+wp80', but the package does not contain any assembly references or content files that are 
compatible with that framework. For more information, contact the package author.

Hopefully in a future version of NuGet it gets better at indicating to the user which PCL profiles a package supports - so that it doesn't even show you these incompatible packages...

Anyway, where were we? Ah yes, Rx.

The Reactive Extensions are a dependency for this package and only supports the first profile (portable-windows8+net45) and has separate profiles for the other platforms. If you look inside the package for Rx-Linq you see it supports these profiles:

• Net40
• Net45
• Portable-Net45-WinRT45
• SL4-WindowsPhone71
• SL5
• WinRT45

So the solution structure for this project becomes:

• Portable-Net45-WinRT45
• Net40
• SL4-WindowsPhone71
• SL5

Which generates these profiles:

• Net40
• Net45 (reusing portable profile)
• Portable-Net45-WinRT45
• SL4-WindowsPhone71
• SL5
• WinRT45 (reusing portable profile)

And that's it!

Footnote: You may notice the lack of WP8 in that list - when NuGet cannot find a specific windowsphone8 profile in a package, it will fall back to the Windows Phone 7.1 (Mango) profile SL4-WindowsPhone71 instead. I tested Rx-Linq and Reactive.EventAggregator in the WP8 simulator and didn't spot any issues. Please log an issue here if you find something odd.

Here's some samples:

Subscribing to an event

// arrange
var eventWasRaised = false;
var eventPublisher = new EventAggregator();

// act
eventPublisher.GetEvent<SampleEvent>()
              .Subscribe(se => eventWasRaised = true);

eventPublisher.Publish(new SampleEvent());

// assert
eventWasRaised.ShouldBe(true);

Disposing of the event

// arrange
var eventWasRaised = false;
var eventPublisher = new EventAggregator();

// act
var subscription = eventPublisher.GetEvent<SampleEvent>()
                                 .Subscribe(se => eventWasRaised = true);

subscription.Dispose();
eventPublisher.Publish(new SampleEvent());

// assert
eventWasRaised.ShouldBe(false);

Selectively subscribing to an event

// arrange
var eventWasRaised = false;
var eventPublisher = new EventAggregator();

// act
eventPublisher.GetEvent<SampleEvent>()
              .Where(se => se.Status == 1)
              .Subscribe(se => eventWasRaised = true);

eventPublisher.Publish(new SampleEvent { Status = 1 });

// assert
eventWasRaised.ShouldBe(true);