Count number of parts in a MEF container

I messed up in my code - I create lots of short-lifetime objects and use MEF to resolve dependencies. As anyone with some MEF experience knows, MEF holds onto a reference on these guys. The result is the short lifetime turns into LOOONNNGGG lifetime. So, this is easy enough to fix - use SatisfysImportsOnce on CompositionContainer.

But I'd like to make this x-check part of my unit tests now so that I don't accidently add an incorrect part into the container (or perhaps I missed one in the code search I just did). Sooo... how to do this?

My code, a bit abstracted, looks something like this:

        _catalog = new AggregateCatalog();
        _container = new CompositionContainer(_catalog);
        _batch = new CompositionBatch();

I then add parts to a batch, and call _container.Compose(_batch). I thought perhaps something like the following would work to get a count, but it always returns zero:

        int nParts1 = _container.开发者_如何转开发Parts.Count();
        int nParts2 = _container.Catalogs.Sum(c => c.Parts.Count());

However, both of those return zero. How can I get this count for tests? It is ok if perf isn't fantastic - this is part of the test, not the running app. Many thanks in advance!

There's not a simple way to do this. You'll need to go digging around in the internal implementation of MEF to find this information. Since the source code is available (mef.codeplex.com) this is quite possible, but still not too simple.