MEF vs. PRISM. What is the difference? What will be supported in the future?

Question

What I want to create is a Silverlight app with a few tabs/modules that will all be separate DLLs.

I see PRISM has the Shell/Module concepts that seem directed towards doing UI and I find a nice demo (showing how to search digg/twitter).

But it sounds like MEF will be included in VS2010 so I would like to go with that option.

Can anyone somehow clearly explain the differences? (I am not a advanced programmer)

Answer 1

MEF and Prism serve two very distinct goals.

Prism is basically guidance for designing composite applications - where you have a shell and "regions" that are dynamically assigned, and integrated. It includes an IoC container (Unity) that it uses for it's injection.

MEF is a dependency injection framework - it's main goal is to "fill in" depedencies at runtime for an application. In this respect, it's filling the same goal as Unity does within Prism (and, in fact, you could pretty easily rework Prism to use MEF instead of Unity).

Prism fills a broader scope, in some respects, but is also really limited to GUI applications. MEF is just doing one thing (Dep. Injection), but geared to be more general purpose, for any type of application.

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As for the lifetime of these products -there is no answer here, but this is kind of how they're being developed:

Prism was developed by the Patterns and Practices team. The goal isn't to necessarily make software, but to provide guidance. As such, they update (although somewhat infrequently) the Prism library and sample, but Prism isn't a core part of the framework shipped by Microsoft. It's really a third party library (even though MS funds a lot of it, most of the P&P people aren't MS FTE).

MEF, from the blog posts, sounds like it is planned to be integrated into the framework, and be used directly inside of MS projects. As such, it's getting heavy development, directly from Microsoft, and being used in their products.

I, personally, have read through the Prism documentation (and have the book), and have gone through the samples. It is very helpful to understand how to break apart an application, but it really is guidance more than a complete, usable framework. The samples are very good at doing what they're designed to do - educate an architect in how to design a composite application.

If your goal is to just keep a clean separation of concerns in a silverlight application, I'd focus more on learning MVVM than necessarily just using Prism.

If you want to use MEF, there are other good options. For example, the WPF Application Framework is an entire MVVM framework built on top of using MEF, and fairly nice.