C++/CLI invoke: object does not match target type

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I'm trying to call a method of a class that was defined in a C# assembly. The calling code is C++/CLI. Problem: I keep getting a System.Reflection.TargetException with message "Object does not match target type."

The assembly has one public class, defined as follows:

C#

namespace CsWorker
{
    public class CsWorkerClass
    {
        public int VoidMethod()
        {
            return 777999;
        }
    }
}

This is a snippet of the calling code. On entry, the variable 'Object^ m_pWorker' contains a ref to an instance of CsWorkerClass and 'MethodInfo^ method' points to CsWorkerClass.VoidMethod. The intention is an equivalent to calling m_pWroker->VoidMethod(). Everything except the last 2 code lines were created to eliminate the more obvious reasons for the exception. The inline comments denote what the variables contain.

C++

auto objType = m_pWorker->GetType();
auto objClassName = objType->FullName; // CsWorker.CsWorkerClass
auto methodClass = method->DeclaringType;
auto methodName = method->Name; // VoidMethod
auto methodParams = method->GetParameters();
auto nParams = methodParams->Length; // 0
auto methodClassName = methodClass->FullName; // CsWorker.CsWorkerClass
_ASSERT(objType == methodClass); // passes
array<Object^>^ arg_dummy;
auto ret = method->Invoke(m_pWorker, arg_dummy/*arglist*/);

The Invoke call in the last line throws a System.Reflection.TargetException with message text "Object does not match target type."

What am I doing wrong here?

What I have tried:

This code fragment is boiled down from a more complex scenario where the method would take several parameters, so that I can rule out a mismatch of parameters.

Googled for a solution, but all solutions which I found say "you must supply the object as the first parameter to Invoke, not the object's type" - which I do.

Posted 12-Sep-23 1:11am

hans.sch

Updated 12-Sep-23 8:08am

Deeksha Shenoy

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Phil J Pearson · Answer 1 · 2023-09-12T04:13:00

Solution 1

Why are you passing a parameter (arg_dummy) to a method that takes no parameters?!

Posted 12-Sep-23 4:13am

Phil J Pearson

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hans.sch 12-Sep-23 12:50pm

@Phil J Pearson - arg_dummy is an empty array which corresponds to the empty parameter list. If I remove it, the compiler complains because Invoke requires 2 parameters. The second parameter to Invoke is of type 'object?[]?'. And in fact arg_dummy is null because I don't assign it a value.

Phil J Pearson 13-Sep-23 6:59am

Sorry; I see now.
I see nothing wrong with your code. I reproduced it in C# and it works. I tried both null and an empty object array as the second parameter to Invoke and both worked. I tried changing the return type of VoidMethod and it still worked without any other changes. I think the problem must be in some code you're not showing.

Maxim Kartavenkov · Answer 2 · 2023-09-13T03:23:00

I think you miss something around m_pWorker and the method also specify the nullptr or create an empty instance of the array arg_dummy
here is an example which will be useful - I made it with just C# but the reflection methods which you should follow is the same.

public class CsWorkerClass
{
    public int VoidMethod()
    {
        return 777999;
    }
}

static void Main(string[] args)
{
    {
        CsWorkerClass c = new CsWorkerClass();
        var t = typeof(CsWorkerClass);
        var m = t.GetMethod("VoidMethod");
        var res = m.Invoke(c, new object[] { });
        Console.WriteLine(res);
    }
    {
        object worker = null;
        {
            var assembly = Assembly.GetExecutingAssembly();
            foreach (var t in assembly.GetTypes())
            {
                if (t.IsClass && t.Name == "CsWorkerClass")
                {
                    worker = Activator.CreateInstance(t);
                    break;
                }
            }
        }
        if (worker != null)
        {
            CsWorkerClass c = new CsWorkerClass();
            var t = worker.GetType();
            MethodInfo mi = null;
            foreach (var m in t.GetMethods())
            {
                Console.WriteLine(m.Name);
                if (m.Name == "VoidMethod")
                {
                    mi = m;
                    break;
                }
            }
            if (mi != null)
            {
                var res = mi.Invoke(worker, null);
                Console.WriteLine(res);
            }
        }
    }
}

hans.sch · Answer 3 · 2023-10-01T09:16:00

Silly me.
In my question, I said that this line causes the exception:

C++

auto ret = method->Invoke(m_pWorker, arg_dummy/*arglist*/);

Further, I said that m_pWorker was declared as Object^. This, of course, wasn't true. Actually, the declaration was msclr::auto_gcroot<Object^>, and the Invoke call should read:

C++

auto ret = method->Invoke(m_pWorker.get(), arg_dummy/*arglist*/);

Sometimes it helps to switch the mind to completely different tasks and then return to the problem :-)

Thanks to you who tried to lead me into the correct direction!

C++/CLI invoke: object does not match target type

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