How to make a simple dynamic proxy in C#

Question

I want to build a dynamic proxy object to add certain functionality to an object.

basically i want to receive an object, wrap it with an object that looks identical to the original i got, and intercept all the calls.

class Wrapper : DynamicProxy// dynamic proxy is not a reall class, but i guess something like this exists...
{
    public static T Wrap(T obj)
    {
        return (T) new Wrapper(obj);
    }

    public override object InterceptCall(MethodInfo info, object[] args)
    {
        // do stuff
    }

}

---

Just to clarify, I want to do something similar to the WCF channel factory...

---

I'm adding a bounty, because I need a good way to proxy classes (not interfaces) and to handle non virtual methods (as if I inherited and added a methond under the "new" keyword). I'm sure all this is very possible as the .Net does it.

Answer 1

You could do this with a combination of DynamicObject and ImpromptuInterface but you will have to have an Interface that implements the functions and properties you want to proxy.

public interface IDoStuff
{
    void Foo();
}

public class Wrapper<T> : DynamicObject
{
    private readonly T _wrappedObject;

    public static T1 Wrap<T1>(T obj) where T1 : class
    {
        if (!typeof(T1).IsInterface)
            throw new ArgumentException("T1 must be an Interface");

        return new Wrapper<T>(obj).ActLike<T1>();
    }

    //you can make the contructor private so you are forced to use the Wrap method.
    private Wrapper(T obj)
    {
        _wrappedObject = obj;
    }

    public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result)
    {
        try
        {
            //do stuff here

            //call _wrappedObject object
            result = _wrappedObject.GetType().GetMethod(binder.Name).Invoke(_wrappedObject, args);
            return true;
        }
        catch
        {
            result = null;
            return false;
        }
    }
}

You could of course choose to lose the type-safety and go with a DynamicObject like I showed and then drop the duck-casting.

I made a transparant extendible version of this object proxy, and open-sourced it here.