Hello,
I'm trying to build a line of business application using Silverlight. I felt like I was doing good then someone asked some questions. Immediately, I became really confused. I see discussions around Prism, Unity, and the Managed Extensibility Framework. However, they all look like they are trying to solve the same problem. Am I nuts? How do these three items compare / contrast with one another?
Thank you!
I recommend listening to the Herding Code podcasts with Glenn Block. (Part 1 and Part 2). He goes into this exactly subject, in much more detail than we can answer here.
That being said -
MEF and Unity are the two things that have quite a bit of overlap. Prism, in its default form, uses Unity for its dependency injection. You can use Prism with MEF, if you like, instead.
Prism is designed more for building composite applications. MEF, on the other hand, is about extensibility. There is definitely some overlap in goals here, but the basic driving factor is different.
The newest guidance I've seen, which I fully agree with, was just posted on Glenn Block's blog: "If you are starting fresh you can use MEF for modularity, and general aspects of your composite app. Where appropriate you can pull in Prism bits."
http://blogs.msdn.com/gblock/archive/2009/12/02/mef-and-prism-to-be-or-not-to-be.aspx
There was this post today that discusses two scenarios where MEF and Prism work together to provide solutions. Each scenario leverages features that are not found in each, with 80/20 rules for those features that they do share.
Although there is overlap, the essential differences from a 30,000 view are
Unity is a IOC container. Use it to make your app more loosely coupled
Prism is gear toward making your UI more loosely coupled. As Reed mentioned, it uses Unity to help do this.
MEF is meant to make your code extensible. This helpful when having to interoperate with code that will be written by someone else. An example is if your application will support plugins.