C# COM => pointer => delphi interface

Question

Couple of days I cant make solution to solve my problem. I have interface and class in C# which visible as COM server. And I have Delphi application where I need to access this interface. But in my case I need in C# side to return 32 bit pointer to interface and at Delphi side - to convert pointer to interface. What is done? c# side. All attributes written well, source code is cutted because original class is much bigger, but idea is understandable:

[ComVisible(true)]
[CLSCompliant(true)]
[Guid("C1A57BD0-AAA2-4AB8-BA2F-ADFA04275AD5")]
[ClassInterface(ClassInterfaceType.None),
 ComSourceInterfaces(typeof(IProcPreviewEndArgs))]
public class ProcPreviewEndArgs : IProcPreviewEndArgs
{

   [ComVisible(true), PreserveSig]
   public IntPtr CreateNew()
   {
       var obj = new ProcPreviewEndArgs();
       GC.SuppressFinalize(obj);
       return Marshal.GetComInterfaceForObject(obj, typeof (IProcPreviewEndArgs));
   }
}

delphi side:

type
  PIProcPreviewEndArgs = ^IProcPreviewEndArgs;

 Index, Res: Integer;
 ppa : IProcPreviewEndArgs;
 pppa : PIProcPreviewEndArgs;

  ppa := CoProcPreviewEndArgs.Create;   // Creates COM object via Delphi services
  ppa.CreateNew(Res);                   // Creates object of the same type, returns as Ret (Integer)
  pppa := PIProcPreviewEndArgs(Res);    // Trying to cast Intereger to interface
  pppa^.CreateNew(Res); // just to test calling posibility

On pppa^ (getting instance by pointer) ACCESS VIOLATION exception is thrown. pointer Res is not null. It is about 60 000 000. Basicly it is kernel space area.

UPD

[CLSCompliant(true), ComVisible(true),
 InterfaceType(ComInterfaceType.InterfaceIsIUnknown),
 Guid("10572D64-B612-468F-86B3-D12F0B6E3CD2")]
public interface IProcPreviewEndArgs
{
    IntPtr CreateNew();
    IntPtr Get(int aMin, int aMax, uint cMin, uint cMax);
    void ToAngle(int x, int y, int w, int h, out int nx, out int ny, out int nw, out int nh);
    IntPtr GetImage();
}

Delphi (generated by Delphi and working well when using standard Delphi methods to manipulate COM objects):

 IProcPreviewEndArgs = interface(IUnknown)
    ['{10572D64-B612-468F-86B3-D12F0B6E3CD2}']
    function CreateNew(out pRetVal: Integer): HResult; stdcall;
    function Get(aMin: Integer; aMax: Integer; cMin: LongWord; cMax: LongWord; out pRetVal: Integer): HResult; stdcall;
    function ToAngle(x: Integer; y: Integer; w: Integer; h: Integer; out nx: Integer; 
                     out ny: Integer; out nw: Integer; out nh: Integer): HResult; stdcall;
    function GetImage(out pRetVal: Integer): HResult; stdcall;
  end;

Delphi version: Delphi XE2

You aren't showing enough code. What is `IProcPreviewEndArgs`? On both sides. And what is `CoProcPreviewEndArgs`? Did that come from your TLB import? — David Heffernan, Sep 03 '12 at 20:04

David Heffernan · Accepted Answer · 2012-09-03T21:04:33.597

I believe that CreateNew returns IProcPreviewEndArgs rather than ^IProcPreviewEndArgs. So your code should read:

var
  ppa1, ppa2: IProcPreviewEndArgs;
....
ppa1 := CoProcPreviewEndArgs.Create;   
ppa1.CreateNew(Res);                   
ppa2 := IProcPreviewEndArgs(Res);    
ppa2.CreateNew(Res);

If I were you I'd declare those Integer return values that map to C# IntPtr as Pointer in Delphi. That way your code will work if ever you compile a 64 bit version.

I'd also contemplate using safecall rather than stdcall and so get the compiler to convert any errors from HRESULT to Delphi exception.

IProcPreviewEndArgs = interface(IUnknown)
  ['{10572D64-B612-468F-86B3-D12F0B6E3CD2}']
  function CreateNew: Pointer; safecall;
  function Get(aMin: Integer; aMax: Integer; cMin: LongWord; cMax: LongWord): Pointer; safecall
  procedure ToAngle(x: Integer; y: Integer; w: Integer; h: Integer; out nx: Integer; 
                    out ny: Integer; out nw: Integer; out nh: Integer); safecall;
  function GetImage: Pointer; safecall;
end;

I also wonder why you have to return untyped pointers in, for example, CreateNew. Why can't you declare that function to return IProcPreviewEndArgs on both sides?

Thank you for your answer. Now it works fine! :) I was confused using Delphi pointers. For future investigations I need to remember that there is no diffenerce between languages in pointers using :) Thank you — Alexus, Sep 04 '12 at 04:18
Main reason why pure pointers, but not Interface pointers is using Win32API to transfer pointers from one library to another (dont ask why, just customer desire) — Alexus, Sep 04 '12 at 04:48

score 1 · Answer 2 · answered Sep 03 '12 at 20:08

Delphi fully supports COM/ActiveX, regardless of where the pointer is coming from.

Q: What version of Delphi are you using?

SUGGESTION:

1) Create a C# test client to test your ProcPreviewEndArgs.CreateNew() method. See if it works.

2) Review this article:

http://delphi.about.com/library/weekly/aa121404a.htm

Change your Delphi code to use COM/ActiveX classes and GUIDS (as opposed to Delphi pointers). Make it work the same as the C# test client you got working in Step 1. Make sure you're doing all the "basics", including calling CoInitialize() somewhere in your Delphi .exe before you start using COM/ActiveX.

3) Please consider if you need COM/ActiveX at all. Perhaps your design can use PInvoke without COM/ActiveX?

Thank you for your reply. Yes, its totally easier to use your way but in my case I need to send pointer via Windows messaging queue (WndProc and so on), where in lParam Im trying to send pointer — Alexus, Sep 03 '12 at 20:11
@Alexus I hope you realise that you cannot send pointers across processes. In other words, the recipient of the message cannot live in a different process. — David Heffernan, Sep 03 '12 at 20:29

C# COM => pointer => delphi interface

2 Answers2