Question

As is asked in this post, I came up with an example that uses Delegate to speedup Refection in .NET/C#.

However, I got this error when running (compilation works fine). What might be wrong?

Unhandled Exception: System.ArgumentException: type is not a subclass of Multicastdelegate
  at System.Delegate.CreateDelegate (System.Type type, System.Object firstArgument, System.Reflection.MethodInfo method, Boolean throwOnBindFailure, Boolean allowClosed) [0x00000] in <filename unknown>:0 
  at System.Delegate.CreateDelegate (System.Type type, System.Reflection.MethodInfo method, Boolean throwOnBindFailure) [0x00000] in <filename unknown>:0 
  at System.Delegate.CreateDelegate (System.Type type, System.Reflection.MethodInfo method) [0x00000] in <filename unknown>:0 
  at EX.RefTest.DelegateTest () [0x00000] in <filename unknown>:0 
  at EX.RefTest.Main () [0x00000] in <filename unknown>:0 

ADDED

This is the (working) source code thanks to the help from Jon & ChaosPandion.

using System.Reflection;
using System;

namespace EX
{
    public class Hello
    {
        // properties
        public int Valx {get; set;}
        public int Valy {get; set;}
        public Hello()
        {
            Valx = 10; Valy = 20;
        }
        public int Sum(int x, int y)
        {
            Valx = x; Valy = y;
            return (Valx + Valy);
        }
    }
    public class RefTest
    {
        static void DelegateTest()
        {
            Hello h = new Hello();
            Type type = h.GetType();
            MethodInfo m = type.GetMethod("Sum");

            // Wrong! Delegate call = Delegate.CreateDelegate(type, m);
            Delegate call = Delegate.CreateDelegate(typeof(Func<int, int, int>), h, m);
            int res = (int) call.DynamicInvoke(new object[] {100, 200});
            Console.WriteLine("{0}", res);
            // This is a direct method implementation from Jon's post, and this is much faster
            Func<int, int, int> sum = (Func<int, int, int>) Delegate.CreateDelegate(typeof(Func<int, int, int>), h, m);
            res = sum(100, 200);
            Console.WriteLine("{0}", res);
        }
        static void Main()
        {
            DelegateTest();
        }
    }
}

ADDED2

Based on Jon’s answer, I did some performance test to use sum 1000 time.
Compared to the method of using (int) call.DynamicInvoke(new object[] {100, 200});, Func<int, int, int> sum = (Func<int, int, int>) Delegate.CreateDelegate(typeof(Func<int, int, int>), h, m); is 300 times faster.

Answer 1

Hello isn’t a delegate type – so you can’t pass it into Delegate.CreateDelegate as the first argument. You need a delegate type with the same parameter types and return type – in this case, something like:

delegate int Foo(int x, int y);

or

Func<int, int, int>

Also note that the overload of Delegate.CreateDelegate you’ve called is meant to be used for a static method – you ought to be using the overload which also takes the target of the delegate (in this case, h).

I have a blog post which shows using Delegate.CreateDelegate for speeding up access. Note that I wouldn’t expect DynamicInvoke to be significantly faster than calling the method directly with reflection… it’s still going to have to check the parameter types etc. Really you want a strongly-typed delegate type called statically (as opposed to dynamically) to make things really fast.