C#

OPC (OLE for Process Control) is a protocol as an interface between
applications and industry hardware drivers. It defines two main components (COM)
registered in opcserver category : OpcServer & OpcGroup.

I have written two corresponding classes as follows that implement the required
Interfaces as defined by OPC.

-----------------------

[Guid( "926EFA52-C020-4259-B879-203512901EAF" )]

[ProgId("FAHM OPC Server 1")]

[ComVisible( true )]

public class OpcServer: IOPCServer, IOPCCommon, IOPCItemProperties,
IOPCBrowseServerAddressSpace

{

//Implementd inteface methods

}





[Guid( "075A7104-076F-481f-8CCF-11BA9AE375EB" )]

[ProgId("FAHM OPC Group 1")]

[ClassInterface(ClassInterfaceType.None)]

public class OpcGroup: IOPCItemMgt, IOPCAsyncIO2, IOPCSyncIO, IOPCGroupStateMgt

{

//Implementd inteface methods

}



I can in a not managed programming language such as delphi or c++ create an
instance of them and call all methods of both of them and QueryInterface them to
all implemented Interfaces and see they are working by showing just a messagebox
for test.

The problem is that the IOPCServer Interface defines a method AddGroup as
follows that returns an instance of OPCGroup and has following signature in c++
and c#:

c++:

virtual HRESULT STDMETHODCALLTYPE AddGroup(

        /* [string][in] */ LPCWSTR szName,

        /* [in] */ BOOL bActive,

        /* [in] */ DWORD
dwRequestedUpdateRate,

        /* [in] */ OPCHANDLE hClientGroup,

        /* [in][unique] */ LONG __RPC_FAR *pTimeBias,

        /* [in][unique] */ FLOAT __RPC_FAR *pPercentDeadband,

        /* [in] */ DWORD dwLCID,

        /* [out] */ OPCHANDLE __RPC_FAR *phServerGroup,

        /* [out] */ DWORD __RPC_FAR *pRevisedUpdateRate,

        /* [in] */ REFIID riid,

        /* [iid_is][out] */ LPUNKNOWN __RPC_FAR
*ppUnk) = 0;

c# :

void AddGroup(

        [In, MarshalAs(UnmanagedType.LPWStr)]
string szName,

        [In, MarshalAs(UnmanagedType.Bool)]
bool bActive,

        [In] int dwRequestedUpdateRate,

        [In] int hClientGroup,

        [In] ref int pTimeBias,

        [In] ref float pPercentDeadband,

        [In] int dwLCID,

        [Out] out int phServerGroup,

        [Out] out int pRevisedUpdateRate,

        [In] ref Guid riid,

        [Out,
MarshalAs(UnmanagedType.IUnknown)] out object ppUnk);

When in the unmanged code call this method of IOPCServer, it seems to be ok, but
the returned object in ppUnk that supposed to be a IOPCItemMgt fails to execute
any of its methods and raises an memory exception.

I tried following implementation for OPCSerevr.AddGroup but all of them have the
same wrong result:

------------------------------------------

impl. 1:

    Type typeofGroup = Type.GetTypeFromProgID( "FAHM OPC Group 1"
);

    if( typeofGroup == null )

    throw new Exception("OPC Server Not Found");

    object grp = Activator.CreateInstance( typeofGroup );

    IntPtr pRes = IntPtr.Zero;

    IntPtr pUnk = Marshal.GetIUnknownForObject(obj);

    Marshal.QueryInterface(pUnk, ref riid, out pRes);

    Marshal.Release(pUnk);

    if (!pRes.Equals(IntPtr.Zero))

        ppUnk = pRes;

    else

       
Marshal.ThrowExceptionForHR(HResult.E_NOINTERFACE);



------------------------------------------

impl. 2:

    object grp = new OpcGroup();

    ppUnk = IntPtr.Zero;

    ppUnk = Marshal.GetComInterfaceForObject(grp,
typeof(IOPCItemMgt));



------------------------------------------

impl. 3:

    object grp = new OpcGroup();

    ppUnk = grp;

------------------------------------------

impl. 4:

    object grp = new OpcGroup();

    ppUnk = (IOPCItemMgt)grp;



And for each of mentioned lines in above implementaions I surrounded it with a
try-catch block and showed messageboxes after each successfull or failed block,
and it seems that none of them fails, but I don't know why the returned
IOPCItemMgt is incorrect.



Can anyone help me?

Special Regards

Umed Kurdistan

unmanaged code :
   1- Create an instance from OPCSerevr --> Is OK & can call all methods when
       casted to any interface
   2- Create an instance from OPCGroup --> Is OK & can call all methods when
       casted to any interface
   3- Call AddGroup method of OPCServer casted to IOPCServer that returns an
       OPCGroup and casting it to any interface is OK, but when i call the
       methods raises a memory error.

public interface IFoo
{
  string Bar {get;}
}

class Foo : IFoo
{
  public string Bar {get{...};set{...};}
}