CODEWITHSUNDEEP
c#.netmef
Venemo
Venemo

Reputation: 19067

MEF: What if I have multiple exports but need only one import?

I'm trying to wrap my mind around MEF. There is one thing I don't understand.

Assume that I have an interface, named ISomething, which is a contract, and I have more than one assemblies in a folder that contains my application, and I have no idea how many ISomething implementations are in them, or which one contains one.

If I create a host application in which I use MEF, and would like to get an ISomething, but only one, how does MEF decide which implementation it will give me?

Or, similarly to a common IoC container, how do I tell it which implementation should it use?

Thanks in advance for your answers.

Upvotes: 13

Views: 7806

Answers (2)

Daniel Plaisted
Daniel Plaisted

Reputation: 16744

See this blog post for a discussion of this issue and some of the options you have. Also, Glenn Block has a blog post describing how to customize the container behavior with defaults.

Upvotes: 14

Reed Copsey
Reed Copsey

Reputation: 564403

In the case of MEF, if you have many Exports that will satisfy an Import, you have two options:

  1. Change your Import around to use [ImportMany]. Decide, at runtime, which of the Imports to use for your contract, potentially just picking the first, or one at random.
  2. Use [ImportMany] in conjunction with Metadata in order to decide which Import to use.

Upvotes: 11

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