unit DllClass;

interface

uses
  ActiveX, ComObj;

const
  CLSID_TDllNumber: TGUID =
  '{84960F62-1D49-11D1-854E-444553540000}';

type
  INumber = interface
    ['{ECD5DAE3-1D37-11D1-854E-444553540000}']
    function GetValue: Integer; stdcall;
    procedure SetValue(New: Integer); stdcall;
    procedure Increase; stdcall;
    function RefCount: Integer; stdcall;
  end;

type
  TDllNumber = class(TComObject, INumber)
  private
    Value: Integer;
  public
    function GetValue: Integer; virtual; stdcall;
    procedure SetValue(New: Integer); virtual; stdcall;
    procedure Increase; virtual; stdcall;
    function RefCount: Integer; stdcall;
    procedure Initialize; override;
    destructor Destroy; override;
  end;

implementation

uses
  Windows, ComServ, SysUtils;

procedure TDllNumber.Initialize;
begin
  inherited;
  Value := 10;
end;

destructor TDllNumber.Destroy;
begin
  inherited;
  MessageBox(0,
    PChar('Object ' + IntToStr(Value) + ' Destroyed'),
    'TDLLNumber', mb_OK); // API call
end;

function TDllNumber.GetValue: Integer;
begin
  Result := Value;
end;

procedure TDllNumber.SetValue(New: Integer);
begin
  Value := New;
end;

procedure TDllNumber.Increase;
begin
  Inc(Value);
end;

function TDllNumber.RefCount: Integer;
begin
  Result := inherited RefCount;
end;

initialization
  TComObjectFactory.Create(
    ComServer, TDllNumber, CLSID_TDllNumber,
    'Md3.FirstCom', 'Md3 First COM Server',
    ciMultiInstance);
end.