Delegate.CreateDelegate ArgumentException not helpful!

I have some code that is supposed to return a delegate of a certain type:

private static RuleSet.RuleDelegate _GetMemberRuleMethodDelegate(string methodName, Type ruleType)
        {
            MethodInfo mi = ruleType.GetMethod(methodName);
            if (mi != null)
            {
                if (mi.IsPrivate)
                    throw new FastReflectorFailException(String.Format(
                        "Rule: '{0}' is private, and cannot be executed directly.", methodName));
                return (RuleSet.RuleDelegate)
                        Delegate.CreateDelegate(typeof(RuleSet.RuleDelegate), mi);
            }
            else
                throw new FastReflectorFailException(String.Format(
                       "Rule: '{0}' does not exist.", methodName));
        }

The idea is that I grab the method by it's string name (methodName), from the Type ruleType. It gets a MethodInfo object, and if the method isn't private, it tries to return a delegate of type RuleDelegate<>, whose signature the methodInfo variable matches (I know for certain it matches because this is a limited test case).

On this line, the code throws an ArgumentException error:

return (RuleSet.RuleDelegate)
                        Delegate.CreateDelegate(typeof(RuleSet.RuleDelegate), mi);

It says "Error binding to target method." Thanks, I can see that.

Anyway, in the metadata of the CreateDelegate method, I found this note about ArgumentException:

        //   System.ArgumentException:
        //     type does not inherit System.MulticastDelegate.-or-type is not a RuntimeType.
        //     See Runtime Types in Reflection. -or- method is not a static method, and
        //     the .NET Framework version is 1.0 or 1.1. -or-method cannot be bound.-or-method
        //     is not a RuntimeMethodInfo. See Runtime Types in Reflection.

I don't know how to tell whether the type inherits from System.MulticastDelegate.
I don't know how to tell whether it's a RuntimeType (but I suspect it is).
I'm using .NET 2.0, so that's not the issue.
I know why the method would be unable to bind.
I know how how to tell whether the method is a RuntimeMethodInfo.

I looked at "Runtime Types in Reflection" on msdn, and it's worthless.

Can someone point me in the right direction?

Hi.

The question is quite old but I faced the same problem and solved it. If you need to create a non-static method delegate, you must give the reference to the object the method belongs to. See the following example how to create a static and instance level method delegate:

    public class Test
    {
        public static void StaticMethod()
        {
            MessageBox.Show("Hello from static method!");
        }

        public void InstanceMethod()
        {
            MessageBox.Show("Hello from instance method!");
        }
    }

    public delegate void TestDelegate();

    public class Test2
    {
        public void CreateAndCallDelegates()
        {
            Test test = new Test();

            Type testType = test.GetType();

            MethodInfo staticMethodInfo = testType.GetMethod("StaticMethod");
            MethodInfo instanceMethodInfo = testType.GetMethod("InstanceMethod");

            TestDelegate staticMethodDelegate = (TestDelegate)Delegate.CreateDelegate(typeof(TestDelegate), staticMethodInfo);
            TestDelegate instanceMethodDelegate = (TestDelegate)Delegate.CreateDelegate(typeof(TestDelegate), test, instanceMethodInfo, true);

            staticMethodDelegate();
            instanceMethodDelegate();
        }
    }

1 Reply

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Antti18y ago
Hi.

The question is quite old but I faced the same problem and solved it. If you need to create a non-static method delegate, you must give the reference to the object the method belongs to. See the following example how to create a static and instance level method delegate:

    public class Test
    {
        public static void StaticMethod()
        {
            MessageBox.Show("Hello from static method!");
        }

        public void InstanceMethod()
        {
            MessageBox.Show("Hello from instance method!");
        }
    }

    public delegate void TestDelegate();

    public class Test2
    {
        public void CreateAndCallDelegates()
        {
            Test test = new Test();

            Type testType = test.GetType();

            MethodInfo staticMethodInfo = testType.GetMethod("StaticMethod");
            MethodInfo instanceMethodInfo = testType.GetMethod("InstanceMethod");

            TestDelegate staticMethodDelegate = (TestDelegate)Delegate.CreateDelegate(typeof(TestDelegate), staticMethodInfo);
            TestDelegate instanceMethodDelegate = (TestDelegate)Delegate.CreateDelegate(typeof(TestDelegate), test, instanceMethodInfo, true);

            staticMethodDelegate();
            instanceMethodDelegate();
        }
    }