Preventing Windows shut down

Question

To detect and prevent shutdown the computer I use very simple program. It has only one form and one private procedure like below:

TForm3 = class(TForm)
private
  procedure WMQueryEndSession(var Msg : TWMQueryEndSession) ;
         message WM_QueryEndSession;
end;

and the implementation

procedure TForm3.WMQueryEndSession(var Msg: TWMQueryEndSession);
begin
  Msg.Result := 0; //so I don't want to shutdown while my program is running
end;

I compiled it Delphi 5 and Delphi 2010. Both of them detect shutdown. But when I compiled in Delphi 2010; after preventing shutdown my program closes. (PC doesn't shutdown)

How do I get the same result from both of them?

Answer 1

EDIT: changed to intercept WM_ENDSESSION instead of WM_QUERYENDSESSION.

As you cannot directly change the behaviour of TApplication, you can install a TApplication message hook instead that neutralizes the WM_ENDSESSION message.

Installing such a hook is quite simple, you only have to add a method similar to the following to your mainform and register the hook in FormCreate.

function TForm25.HookEndSession(var Message: TMessage): Boolean;
begin
  result := false;
  if Message.Msg = WM_ENDSESSION then begin
    Message.Result := 0;
    result := true;
  end;
end;

procedure TForm25.FormCreate(Sender: TObject);
begin
  Application.HookMainWindow(HookEndSession);
end;

Answer 2

I usually run "shutdown -a" command. You can do the same from your code to interrupt Windows from shutdown.

Regards