.NET and PB COM Server

[Petr Schreiber]

Hi all,

I was awaiting PB9 impatiently, as I was looking forward to have OOP tool ( no more "and it is not OOP right?" on university, heh ) able to produce COM servers to be used in other languages ... which would mean I could code in my precious PB and let others struggle with .NET languages.

So the thing I wanted to create is COM DLL to be used with C# ( MSVS 2005 Express ).

What I managed:

• Create DLL
• Use PBTYP to insert type library
• Register server using regsvr32
• In C# "Add reference / DummyCOM" succeeded without any complaints, intellisense sees methods

But the problem is C# does complain "The type does not have constructors declared".
What a weird thing? You can see I have constructor in my code:

Code Select Expand


#COMPILE DLL
#DIM ALL

#RESOURCE "COMServer.pbr"
#COM NAME "DummyCOM", 1.0
#COM TLIB ON
#COM DOC "DummyCOM"
#COM GUID GUID$("{9C41D1BB-3B61-4BA3-A1F1-6FC09A46D9BF}")

#INCLUDE "Win32API.inc"

GLOBAL ghInstance AS DWORD
FUNCTION LIBMAIN (BYVAL hInstance   AS LONG, _
                  BYVAL fwdReason   AS LONG, _
                  BYVAL lpvReserved AS LONG) AS LONG

    SELECT CASE fwdReason
        CASE %DLL_PROCESS_ATTACH
            ghInstance = hInstance
            FUNCTION = 1   'success!
        CASE %DLL_PROCESS_DETACH
            FUNCTION = 1   'success!
        CASE %DLL_THREAD_ATTACH
            FUNCTION = 1   'success!
        CASE %DLL_THREAD_DETACH
            FUNCTION = 1   'success!
    END SELECT
END FUNCTION

CLASS MYCLASS GUID$("{065A1E0F-ACFD-42F8-8DC7-B135168D7C91}") AS COM

  ' -- Isn't this nice example of constructor :")
  CLASS METHOD CREATE ALIAS "CREATE"()
    MSGBOX "Created, yahoo"
  END METHOD

  INTERFACE GREETINGS  GUID$("{AE6D5037-4C8C-471D-ACD5-2AAA664466B7}")
    INHERIT IUNKNOWN
    METHOD HELLO ALIAS "HELLO"()
      MSGBOX "Hello"
    END METHOD

    METHOD CIAO ALIAS "CIAO"()
      MSGBOX "CIAO"
    END METHOD
   
  END INTERFACE
 
END CLASS


But when I try following code in C# I get that silly error. Maybe it is because CREATE is out of INTERFACE so invisible somehow?

...

using DummyCOM;

...

MYCLASS x = new MYCLASS(); ' -- This fails
x.HELLO();  ' -- The hello method was correctly detected by intelisense

I am sorry I am bothering you with .NET stuff, but you can imagine I would be very happy coding everything in PB I trust, and let other use it from C# which I do not like.


Thanks,
Petr

[José Roca]

 
COM classes don't have a constructor. Its lifetime is controlled by the AddRef and Release methods of the IUnknown interface, and its creation by the IClassfactory interface. If PB classes have a constructor, a destructor, and private and hidden methods, is just to allow some OOP programming, but these methods aren't referenced in the virtual table. If C# complains about the class not having a constructor, maybe it is confusing it with a .NET class.

[Petr Schreiber]

Aha,

so maybe I should invoke it differentely.
Thanks a lot for your time José.


Petr

[Patrice Terrier]

Petr,

When using my GDImage.DLL with C#, i am just doing the same than calling the good old FLAT API 

If you compare the GDImage Carousel C# and PB's demo you will see no difference.

I am encapsulating my own API into a dedicated C# class, i put my Win32 DLL in the same folder than my managed EXE and i am done.

[Petr Schreiber]

Hi Patrice,

thanks. I know how to bind classic DLL, but I wanted to avoid the class definition on C# side.
That was the reason why to pick COM DLL instead of good old "normal" DLL under PowerBASIC.

Maybe it will be less work for me to provide C# wrapper class, but then the beauty of COM server is gone, will investigate further.


Petr

[Carlo Pagani]

Hi Petr

Maybe this link will be useful
http://msdn.microsoft.com/en-us/library/ms973274.aspx

Regards - Carlo

[Petr Schreiber]

Hi Carlo,

thanks for the help. That is very good article.

- I tried to create the same DLL as is in article like:

Code (thinbasic) Select Expand


#COMPILE DLL "MSDNCom.DLL"
#DIM ALL


#RESOURCE "COMServer.pbr"
#COM NAME "DummyCOM", 1.0
#COM TLIB ON
#COM DOC "DummyCOM"
#COM GUID GUID$("{9C41D1BB-3B61-4BA3-A1F1-6FC09A46D9BF}")

CLASS MSDNComServer GUID$("{065A1E0F-ACFD-42F8-8DC7-B135168D7C91}") AS COM

  INTERFACE IMSDNComServer GUID$("{AE6D5037-4C8C-471D-ACD5-2AAA664466B7}")
   
    INHERIT IDISPATCH
    METHOD SquareIt ALIAS "SquareIt"()
      MSGBOX "It should square it here"
    END METHOD

  END INTERFACE

END CLASS   


- I used TlbImp to create Interop.MSDNCom.DLL

- I used ildasm.exe to see everything looks the same as in article sample, it does

- I created sample similar to the provided, but still get that constructor problem


I will check the full C++ code again ( it looks very complex ), but so far I had no success.


Thanks,
Petr

[Gérôme Guillemin]

Hello,

True.
This DLL can not be instanciated from .NET as a New object :

Code Select Expand


Dim j As New DummyCOM.MSDNCOMSERVER '=>> Impossible because there is a Private internal mechanism unavailable for .NET


But this coce is possible :

Code Select Expand


Dim j As DummyCOM.MSDNCOMSERVER


But... when we try to invoke the SquareIt() method then .NET crashes.

Same problems appear in VB6 and in VBA as well...
And please I don't want to use the late binding aka CreateObject(""), but plain and direct IDispatch interface

[Edwin Knoppert]

The latest PB release has updated the typelib issue.
A comserver can now be instantiated using new just fine.
(Early binding)

[Petr Schreiber]

Hi Edwin,

thanks for letting us now - I can confirm I just recompiled code and now it works in MSVS C# 2008.


Petr

[Gérôme Guillemin]

Hi Edwin,

thanks for letting us now - I can confirm I just recompiled code and now it works in MSVS C# 2008.


Petr

May be this enhancement was (also) due to my remarks onto the PB forum...