circular dependencies between dlls with visual studio

Question

I have a circular dependency between two functions. I would like each of these functions to reside in its own dll. Is it possible to build this with visual studio?

Answer 1

You need to decouple the two DLLs, placing the interfaces and implementation in two different DLLs, and then using late binding to instantiate the class.

---

// IFoo.cs: (build IFoo.dll)
    interface IFoo {
      void foo(int i);
    }

    public class FooFactory {
      public static IFoo CreateInstance()
      {
        return (IFoo)Activator.CreateInstance("Foo", "foo").Unwrap();
      }
    }

---

// IBar.cs: (build IBar.dll)
    interface IBar {
      void bar(int i);
    }

    public class BarFactory {
      public static IBar CreateInstance()
      {
        return (IBar)Activator.CreateInstance("Bar", "bar").Unwrap();
      }
    }

---

// foo.cs: (build Foo.dll, references IFoo.dll and IBar.dll)
    public class Foo : IFoo {
      void foo(int i) {
        IBar objBar = BarFactory.CreateInstance();
        if (i > 0) objBar.bar(i -i);
      }
    }

---

// bar.cs: (build Bar.dll, references IBar.dll and IFoo.dll)
    public class Bar : IBar {
      void bar(int i) {
        IFoo objFoo = FooFactory.CreateInstance();
        if (i > 0) objFoo.foo(i -i);
      }
    }

The "Factory" classes are technically not necessary, but it's much nicer to say:

IFoo objFoo = FooFactory.CreateInstance();

in application code than:

IFoo objFoo = (IFoo)Activator.CreateInstance("Foo", "foo").Unwrap();

because of the following reasons:

1. You can avoid a "cast" in application code, which is a good thing
2. If the DLL that hosts the class changes, you don't have to change all the clients, just the factory.
3. Code-completion still wroks.
4. Depending on your needs, you have to call culture-aware or key-signed DLLs, in which case you can add more parameters to the CreateInstance call in the factory in one place.

-- Kenneth Kasajian