Delphi in a Nutshell

Name

DispCallByIDProc Variable

Syntax

var DispCallByIDProc: Pointer;

type
  PDispRec = ^TDispRec;
  TCallDesc = packed record
    CallType: Byte;
    ArgCount: Byte;
    NamedArgCount: Byte;
    Args: array[0.255] of Byte;
  end;
  TDispDesc = packed record
    Dispid: Integer;
    ResultType: Byte;
    CallDesc: TCallDesc;
  end;
procedure CallProc(Result: Pointer; const Dispatch: IDispatch;
  DispDesc: PDispDesc; Params: Pointer); cdecl;

DispCallByIDProc := @CallProc;

Description

Delphi calls the DispCallByIDProc procedure to call a dispatch method that is identified by dispatch identifier in a dispinterface. Delphi fills the DispDesc record with the necessary information about the dispatch identifier and the method’s formal parameters. Params points to the actual arguments for the method call. The procedure must store the result in the memory buffer pointed to by Result. The type of Result’s buffer is dictated by the dispatch descriptor.

The default value of DispCallByIDProc is a procedure that raises runtime error 17 (EVariantError).

Tips and Tricks

• The ComObj unit sets DispCallByIDProc to a procedure that implements the necessary code to call IDispatch.Invoke. ComObj also declares the TCallDesc and TDispDesc types.

• Writing your own DispCallByIDProc is a major undertaking. Consult the ComObj.pas source code to learn how.

See Also

Cdecl Directive, Dispid Directive, Dispinterface Keyword, IDispatch Interface, VarDispProc Variable