Creating a Delegate from methodInfo in Mono 2.8.2

Question

Hi I am trying to create a messenger in Mono 2.8.2 - the subset used by Unity3d. I thought it would be nifty to create a helper to auto subscribe methods to the messenger when they are decorated with a "subscribe" attribute.

I've been scratching my head over this and have read many of the other related stack questions without a solution to my problem. Frankly, I don't know if I am doing something wrong or if this is a bug in Mono.

foreach (var methodInfo in methods)
        {
            var attr = methodInfo.GetAttribute<SubscribeAttribute>();
            if (attr == null)
                continue;

            var parmas = methodInfo.GetParameters();
            if (parmas.Length != 1)
            {
                Debug.LogError("Subscription aborted. Invalid paramters.");
                continue;
            }

            var type = parmas[0].ParameterType;

            // Crashes here
            // ArgumentException: method argument length mismatch
            // I have tried many combinations.. 
            // Direct typing of the message type and dynamic typing

            var action = (Action<object>)Delegate.CreateDelegate(typeof(Action<object>), methodInfo);

             // also does not work
             // var dt = Expression.GetActionType(parmas.Select(o => o.ParameterType).ToArray());
             // var action = Delegate.CreateDelegate(dt, methodInfo);

            Subscribe(type, action, instance);
        }

Any suggestions or work around would be appreciated.

Edit The method signature looks like :

[Subscribe]
void OnMessage(object message){
  // Hello World
}

Though, it was originally...

[Subscribe]
void OnTestMessage(TestMessage message){
  // Hello World
}

Answer 1

It's a non-static method and you didn't provide a target object. Therefore Delegate.CreateDelegate will create an "open delegate" with an explicit this argument.

Because of the required this argument, it no longer matches the signature.