Hello all,
i have problems to implement a structure including a callback function
pointer correctly in C# .NET.
The structure is used as a parameter for a initializing function, which
is implemented in a C++ dll (unmanaged code) i want to use.

THEME: calling a DLL-function from .NET including a function pointer
within a class/structure - interop / marshal

First i made a declaration for the function:

        [DllImport("mydll.dll", CharSet = CharSet.Ansi)]
        private static extern System.Int32 Initialize(ref PARAM para);

        //in the dll-documentation it is declared like this. long must now be
a int, the datatypes increased in .NET
        //long Initialize( PARAM *para );

        // and the structure is originally
       //typedef struct
       //{
       //    DWORD   MacNo;
       //    DWORD   OwnPort;
       //    DWORD   IpAddr;
       //    DWORD   Port;
       //    VOID (*CallBack)(DWORD, DWORD, VOID *);
                                   /* Call back routine */
       //    WORD    Timeout[20];
       //    WORD    retry[20];
       //} PARAM ;

then i defined the structure in my code as follows:

        [StructLayout(LayoutKind.Sequential)]
            public class PARAM
        {
            public System.Int32 nMacNo;
            public System.Int32 nOwnPort;
            public System.Int32 nIpAddr;
            public System.Int32 nNCPort;

            [MarshalAsAttribute(UnmanagedType.FunctionPtr)]
            public CallbackFunctionHandler cb;

            [MarshalAs(UnmanagedType.ByValArray, SizeConst=PARA_ARR_LEN)]
            public System.Int16[] arrTimeout = new System.Int16[PARA_ARR_LEN];

            [MarshalAs(UnmanagedType.ByValArray, SizeConst=PARA_ARR_LEN)]
            public System.Int16[] arrRetry = new System.Int16[PARA_ARR_LEN];
        }

and i created a delegate as a funtion pointer:

         // member
        public delegate void CallbackFunctionHandler(System.UInt32 iHandle,
System.UInt32 iEvent, IntPtr arg);
        CallbackFunctionHandler callBackFunctionHandler = new
CallbackFunctionHandler(CallBack);

later on in my code i fill the structure with values and try to call
the initialize function

    // PARAM para = new PARAM(); member
    para.cb = callBackFunctionHandler;
    //...and all other values

    // call the function seems not be ok, but i get no error
    int nResult = Initialize(ref para);

    // and the function which should be called if data arrived
    public static void CallBack(System.UInt32 iHandle, System.UInt32
iEvent, IntPtr arg)

I've tried now so many things and attributes, also with keyword
"unsafe", but i don't get it to work, the tread within the dll is not
started after invoking the initialize function.
It would be nice to know how a callback function pointer must be
marshalled to the unmanaged dll.
Any help would be appreciated.
Martin