如何避免MEF中的多余导入？

Question

Here's the issue... if I use, say a directory catalog in MEF and have some.dll and copy of some.dll, i will get double the exports, even though they are defining the same type, is there a way to resolve this?

EDIT: the problem isn't with this particular issue, this is just an abstract example of a real issue, for instance, if i have an "extensions" folder, and a way to manually import... it's just something that would be nice to handle.

Answer 1

You can do this with a FilteredCatalog (not part of the core MEF distribution.) See the example here: http://mef.codeplex.com/wikipage?title=Filtering%20Catalogs

Rather than selecting from the inner catalogs via Where you may use Distinct . To compare ComposablePartDefinition s for equality the simplest option is to use ToString but casting to ReflectionComposablePartDefinition is also an option.

HTH, Nick

Answer 2

is there a way to resolve this?

Two options come to mind:

• remove the redundant copy of the assembly
• don't use a directory catalog. You can add assembly catalogs for each individual assembly, and just leave out the unwanted assemblies.