Tuesday, November 24, 2009

MEF Contrib for Silverlight 3 (Unofficial)

I’m happy to announce that I’ve completed porting the most recent MEF Contrib (0.7) project to SL3. The project has also been updated to use the most recent MEF release which is beta 2 (Preview 8) as of this writing. All the unit tests from the project pass in the SL environment, here are the screenshots:

image image image

Before I dig into the changes I had to make in order to make it work on SL3, I will focus on NUnit for SL.

As all of you probably know, it is possible to run NUnit tests in SL environment. Microsoft has released a library called Microsoft.Silverlight.Testing which enables developers to execute tests on SL’s CLR. This library ships out of the box with the implementation of MS Tests. However, its extensibility allows to write custom providers for other testing frameworks. Jeff Wilcox wrote a post about running NUnit tests in the SL environment here. He did two things: ported a subset of NUnit to SL, and wrote a provider which enables running NUnit tests using Microsoft.Silverlight.Testing framework. However, his NUnit implementation is very limited, so I googled a little and found a guy who ported NUnit 2.5.1 to SL (you can find his post here). So, for the testing purposes I used mentioned NUnit 2.5.1 SL port together with a provider developed by Jeff. I must admit here, that I’m not sure whether all the features from NU 2.5.1 work correctly in the SL environment. Hopefully, it seems that all the Assert methods including Assert.That and Throws work as expected.

As far as MEFContrib project is concerted, I didn’t have to introduce many modifications. MefContrib.Extensions.Generic project runs without any changes. MefContrib.Integration.Unity project didn’t need to be changed in terms of its implementation. However, all stubs used in unit tests were declared as internal, and it seems MEF for SL has some troubles while instantiating non public members (or SL policy doesn’t allow this?) so most tests were failing. Fortunately, changing access to public repaired everything :) The story is a bit different for the MefContrib.Models.Provider project. This project adds to MEF custom provider model with three programming models built on top of it. These three programming models are

  • Attributed – as it name suggest, parts are registered using attributes,
  • Configurable – parts get registered via App.config,
  • Fluent – parts are registered through method invocation.

The problem lays in the Configurable programming model, because it is implemented using System.Configuration namespace, which is not available to SL programmers. Thus, MefContrib.SIlverlight does not support this model.

The last trouble I had was with two test, which reside in MemberInfoServicesTests test fixture, namely

  • GetMemberInfoShouldReturnMemberIfMemberNameIsSupplied,
  • GetMemberInfoShouldReturnTypeIfMemberNameNotIsSupplied.

Both unit tests test MemberInfoServices class. Both were throwing an exception telling that the test assembly (MefContrib.Models.Provider.Tests) cannot be loaded or the assembly has already been loaded but the versions doesn’t match. To cut the long story short, it turned out that the following code was the root cause (code like the presented below is executed in MemberInfoServices.GetMemberInfo method in both tests) :

Type.GetType("MefContrib.Models.Provider.Tests.FakePropertyPart, MefContrib.Models.Provider.Testsl", false, true)
Don’t know why this doesn’t work. However, a simple modification like follows did the job :)

Type.GetType("MefContrib.Models.Provider.Tests.FakePropertyPart, MefContrib.Models.Provider.Tests, Version=, Culture=neutral, PublicKeyToken=null", false, true)
To maintain separate versions of both tests for regular CLR and SL, I used SILVERLIGHT compiler flag.

Please note that this version is an unofficial release, not available through codeplex.com site. However, I will put an effort to make this an official release or make next MefContrib release based on this one.

Full source code is available on my code gallery here.


Manager said...

Nice job Piotr. Thanks a lot, I'll test this soon !

Glenn Block said...

Good work Piotr, exciting to see contrib getting some new life blood.

wsxwhx694 said...

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