wpf/c# COM being called from C

See more:

C

C#

COM

WPF

I am using c# with wpf to create a class library, I am exporting this as COM interface. I am trying to call this com object from plain C. I have managed to get it working in C++ but am struggling to get it working in plain C.

so I am using the follwing code in c# to create the com interface.

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Windows.Interop;
using System.Linq;
using System.Text;


namespace WPF_TEST
{
    [ComVisible(true)]
    [Guid("92ce2a56-c61f-486c-8854-4d8d88626ba9")]
    public interface ITestWPFInterface
    {
        [DispId(1)]
        void TestWPF();
    }
    [ComVisible(true)]
    [Guid("62e2ed3c-5c2a-48c5-851b-e0b1f6daa9cd"),
    ClassInterface(ClassInterfaceType.None)]

    public class TestWPFInterface : ITestWPFInterface
    {
        public void TestWPF()
        {
            WPF_TEST.MainWindow window = new WPF_TEST.MainWindow();
            window.ShowDialog();
        }


    }

}  

this code is then packaged into a class library and "register for com interop" is ticked.

I am following the jeff glatt tutorial using the following code in plain c to try and pick up this COM object
Header file

#ifndef _ITESTWPFINTERFACE_H_
#define _ITESTWPFINTERFACE_H_

#include <initguid.h>


// Our IExample object's GUID
// original {6899A2A3-405B-44d4-A415-E08CEE2A97CB}
// porting guid ("62e2ed3c-5c2a-48c5-851b-e0b1f6daa9cd")
DEFINE_GUID(CLSID_ITestWPFInterface, 0x62e2ed3c, 0x5c2a, 0x48c5, 0x85, 0x1b, 0xe0, 0xb1, 0xf6, 0xda, 0xa9, 0xcd);

// Our IExample VTable's GUID
// original {74666CAC-C2B1-4fa8-A049-97F3214802F0}
// porting Guid("92ce2a56-c61f-486c-8854-4d8d88626ba9")
DEFINE_GUID(IID_ITestWPFInterface, 0x92ce2a56, 0xc61f, 0x486c, 0x88, 0x54, 0x4d, 0x8d, 0x88, 0x62, 0x6b, 0xa9);

// Defines IExample's functions (in a way that works both for our COM DLL
// and any app that #include's this .H file
#undef  INTERFACE
#define INTERFACE   ITestWPFInterface

/*PROBLEM HERRREEEEE */

DECLARE_INTERFACE_ (INTERFACE, IUnknown)
{
   STDMETHOD  (QueryInterface)      (THIS_ REFIID, void **) PURE;
   STDMETHOD_ (ULONG, AddRef)       (THIS) PURE;
   STDMETHOD_ (ULONG, Release)      (THIS) PURE;
   STDMETHOD  (TestWPF)         (THIS) PURE;

};

#endif 

C file

i initialise and get as far as creating the instance and releasing the class factory

#include <stdio.h>
#include <windows.h>
#include <objbase.h>
#include "ITestWPFInterface.h"

int main( int argc, const char* argv[] )
{
	ITestWPFInterface		*exampleObj;
	IClassFactory	*classFactory;
	HRESULT			hr;
   HRESULT			hres;
   int result;
   if (!CoInitialize(0))
	{
          result = GetLastError();
          // Get WPF.DLL's IClassFactory
	  if ((hr = CoGetClassObject(&CLSID_ITestWPFInterface,CLSCTX_INPROC_SERVER,0,&IID_IClassFactory,&classFactory)))

MessageBox(0, "Can't get IClassFactory", "CoGetClassObject error", MB_OK|MB_ICONEXCLAMATION);
      else
		{
        
			// Create a wpf object
	     if ((hr = classFactory->lpVtbl->CreateInstance(classFactory,0,&IID_ITestWPFInterface,&exampleObj)))
			{
		classFactory->lpVtbl->Release(classFactory);
				MessageBox(0, "Can't create ITestWPFInterface object", "CreateInstance error", MB_OK|MB_ICONEXCLAMATION);
			}
         else
         {
           result = GetLastError();
            // Release the IClassFactory. We don't need it now that we have the one
				hr  =classFactory->lpVtbl->Release(classFactory);
          
            // HERE IS WHERE THE PROBLEM OCCURS RETURNS A E_POINTER
            // the com object definitely is available as i have accessed it from a C++ project
           // Call SetString to set the test wpf
           hres = exampleObj->lpVtbl->TestWPF(exampleObj);
           
           
           
           // Release the com now that we're done with it
          
           exampleObj->lpVtbl->Release(exampleObj);
          
         }
         
      }
               // When finally done with OLE, free it
		CoUninitialize();
	}
       else
		MessageBox(0, "Can't initialize COM", "CoInitialize error", MB_OK|MB_ICONEXCLAMATION);
	        return(0);

}
// this builds ok but this returns an E_POINTER error and I get an error that says that 'The value of ESP was not properly saved across a function call. This is usually a result of calling a function declared with one calling convention with a function pointer declared with a different calling convention.'

ANY IDEAS?