Question

I’ve created a COM object with Visual Studio that I want to use with Delphi.

[Guid("9D0CCD2D-75E9-46AC-BC40-C4D84669FC45")]
[InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
public interface IMyComClassDispatch
{
    string PropertyString { get; set; }
    string funcGetString();
    void funcSetString(string aString);
}

[ClassInterface(ClassInterfaceType.None)]
public class MyComClassDispatch : IMyComClassDispatch
{
    public string PropertyString { get; set; }


    public string varString;

    public string funcGetString()
    {
        return varString;
    }

    public void funcSetString(string aString)
    {
        varString = aString;
    }
}

Then I’ve generated the tlb file, and finally a pascal file corresponding to my COM object with tlibimp.exe bundled with Delphi 5:

C:\>tlibimp.exe -P+ mylib.tlb

and here is the generated code:

// *********************************************************************//
// DispIntf:  IMyComClassDispatch
// Flags:     (4096) Dispatchable
// GUID:      {9D0CCD2D-75E9-46AC-BC40-C4D84669FC45}
// *********************************************************************//
  IMyComClassDispatch = dispinterface
    ['{9D0CCD2D-75E9-46AC-BC40-C4D84669FC45}']
    property PropertyString: WideString readonly dispid 1610743808;
    function  funcGetString: WideString; dispid 1610743810;
    procedure funcSetString(const aString: WideString); dispid 1610743811;
  end;

The problem is that my property is marked as read only and I don’t really see why that is happening, because this tool can also generates C++ code and the property can be modified:

// *********************************************************************//
// Interface   : IMyComClassDispatch
// Indicateurs : (4096) Dispatchable
// GUID        : {9D0CCD2D-75E9-46AC-BC40-C4D84669FC45}
// *********************************************************************//
interface IMyComClassDispatch : public TDispWrapper<IDispatch>
{
  BSTR __fastcall get_PropertyString()
  {
    _TDispID _dispid(/* PropertyString */ DISPID(DISPID_UNKNOWN/*[1610743808]*/));
    TAutoArgs<0> _args;
    OlePropertyGet(_dispid, _args);
    return _args.GetRetVariant();
  }

  void __fastcall set_PropertyString(BSTR Param1/*[in]*/)
  {
    _TDispID _dispid(/* PropertyString */ DISPID(1610743808));
    TAutoArgs<1> _args;
    _args[1] = Param1 /*[VT_BSTR:0]*/;
    OlePropertyPut(_dispid, _args);
  }

  BSTR __fastcall funcGetString()
  {
    _TDispID _dispid(/* funcGetString */ DISPID(DISPID_UNKNOWN/*[1610743810]*/));
    TAutoArgs<0> _args;
    OleFunction(_dispid, _args);
    return _args.GetRetVariant();
  }

  void __fastcall funcSetString(BSTR aString/*[in]*/)
  {
    _TDispID _dispid(/* funcSetString */ DISPID(DISPID_UNKNOWN/*[1610743811]*/));
    TAutoArgs<1> _args;
    _args[1] = aString /*[VT_BSTR:0]*/;
    OleProcedure(_dispid, _args);
  }


  __property   BSTR            PropertyString = {read = get_PropertyString, write = set_PropertyString};
};

Does this means that I should avoid properties with COM objects or is there any options that I should change ? Is this a problem with tlibimp or a limitation of the compiler that cannot generate instructions to write on COM objects properties ?

Any help would be appreciated on this!

Answer 1

This is known defect in Delphi 5 & 6 tlibimp.exe. You shall upgrade to Delphi 7 or newer version to avoid it.