New Post: Use MEF to allow only 2 instances at max per application

Hi there,

Creation policy (e.g. sharing) applies to parts, while one part may have many exports. This is just how the MEF component model works - in most situations this turns out to be useful.

To achieve what you want in a more MEF-like way:

1. Don't make MyClass a part at all:
   

public class MyClass { }

1. Create a separate class that holds and exports the two instances as properties:
   

public class MyClassConfig
{
   MyClass _inst1 = new MyClass();
   MyClass _inst2 = new MyClass();

   [Export("Condition-1")]
   public MyClass Inst1 { get { return _inst1; } }

   [Export("Condition-2")]
   public MyClass Inst2 { get { return _inst2; } }
}

This is the basic approach, anyway - you can tinker with MyClassConfig to implement lazy construction etc. if this is needed.

Hope this simplifies things!
Nick