Preventing Windows shut down

开发者_StackOverflow中文版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?

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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;

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

Regards

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This looks like a bug in Delphi. I suggest you to post this on Quality Central.

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Edit: Here's an approach that doesn't work. Thanks

Procedure TMyForm.FormClose(Sender: TObject;  Var Action: TCloseAction);
Begin
  Action := caNone;  //The form is not allowed to close, so nothing happens.
End;                 // Note: the OP says he tried this, doesn't help. See the comments.

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Are you testing on the same OS? There are some application shutdown changes in Vista. Read this: Application Shutdown Changes in Windows Vista

If you are testing on the same OS, maybe Delphi 2010 handles WM_ENDSESSION messages in a different way. In Delphi 7, WM_ENDSESSION message are handled in Application.WndProc.

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In all versions should you not be using the FormCloseQuery event?

procedure TForm3.FormCloseQuery(Sender: TObject; var CanClose: Boolean);
begin
  Canclose := Not StillDoingImportantStuff;
end;

Oops - just read comments to "this does not work" :( Is win 7 different?

In all my apps this gets called if windows is trying to shut down...

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ShutdownGuard is built with Delphi and it's open source, you can download it tweak it for your needs