How to make a simple dynamic proxy in C#

Solution 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.

Solution 2:

In addition to Castle.DynamicProxy, there is also LinFu.DynamicProxy on Github.

Solution 3:

I should have written this sooner, but never mind.

My issue had a special "gotcha" I needed to be able to proxy classes and not interfaces.

There are two solutions to this:

1. RealProxy and friends, basically means using .NET Remoting. Requires one to inherit from ContextBoundObject.

   • This approach takes advantage of "magic" provided by the .NET JIT compiler (which is hardcoded to specifically recognize RealProxy) to let you "override" non-virtual members.

2. Building a proxy using System.Reflection.Emit as done by spring you can also look at the code of their ProxyFactoryObject. Here are another three articles on the subject.

   • This approach has the crucial disadvantage of limiting you to overriding only virtual members.