System.NullReferenceException in Interop

[sergi]

Hi there,

I am getting a System.NullReference exception when calling an unmanaged
method CreateClassEnumerator. I am really new to Interop, so that I am
having trouble finding out a solution. The code is the following :

<code>

using System;

using System.Runtime.InteropServices;

using System.Collections;

namespace COMInterop1

{

/*
[

object,

uuid(29840822-5B84-11D0-BD3B-00A0C911CE86),

pointer_default(unique)

]
interface ICreateDevEnum : IUnknown

{

import "oaidl.idl";

HRESULT CreateClassEnumerator(

[in] REFCLSID clsidDeviceClass,

[out] IEnumMoniker ** ppEnumMoniker,

[in] DWORD dwFlags);

}*/
[//System device Enumerator Import, implements ICreateDevEnum
Guid("62BE5D10-60EB-11d0-BD3B-00A0C911CE86"),ComImport]

public class SystemDeviceEnumerator

{

}

//Managed declaration of ICreateDevEnum

[Guid("29840822-5B84-11D0-BD3B-00A0C911CE86"),
InterfaceType(ComInterfaceType.InterfaceIsIUnknown )]

interface ICreateDevEnum {

void CreateClassEnumerator([In] Guid clsidDeviceClass, [Out] out
UCOMIEnumMoniker ppEnumMoniker, [In] UInt32 dwFlags);

}

public class Tester

{
static void Main ()

{

Guid deviceClass = new Guid("860BB310-5D01-11d0-BD3B-00A0C911CE86");
UCOMIEnumMoniker EnumMon;
UInt32 dFlag = 0;
SystemDeviceEnumerator de = new SystemDeviceEnumerator();

ICreateDevEnum Ide = (ICreateDevEnum)de;

try

{

Ide.CreateClassEnumerator(deviceClass, out EnumMon, dFlag);
}

catch (Exception e)

{

Console.WriteLine(e.ToString());

Console.Read();

}

}

}

}

</code>