Share code between projects in a solution in Visual Studio 2008, when building a common assembly is impossible

I create an add-on for the product Foo. There are different versions of Foo, namely version 1, 2, 3 and 4.

These versions have a mostly compatible API, but not fully.

I currently have 5 projects:

• DotNetCommon - here are the common methods which could be used if I create an add-on or something other than the Foo product.
• FooOne
• FooTwo
• FooThree
• FooFour

The Foo*-projects contains the add-in for version 1-4 of Foo.

There are a lot of duplicated files in the Foo*-projects, as there are a lot of things in the API which are identical for all versions of Foo. It would be nice to separate out everything which is common for all Foo-versions.

Why not just create a common assembly for开发者_JAVA技巧 all versions of Foo called FooCommon?

If I would put all classes which are common for all versions of Foo into a new library project, I would still have to choose which version of Foo the new FooCommon should reference. As said, they are not identical.

---

Create an interface containing the common methods:

public interface IFoo
{
   void CommonMethod1();
   void CommonMethod2();
}

Create an abstract base class from IFoo:

public abstract class FooBase : IFoo
{
   // Implement the common calls here
   public void CommonMethod1()
   {
      // concrete shared code goes here
   }
   public void CommonMethod2()
   {
      // concrete shared code goes here
   }
}

Create your one-off code from the FooBase:

public class FooOne : FooBase 
{    
   // concrete code specific to FooOne goes here 
}



public class FooTwo : FooBase 
{    
   // concrete code specific to FooTwo goes here 
}