Detecting Windows shutdown

When Windows is shutting down, it sends a WM_QueryEndSession to all open applications. To detect (and prevent shutdown), you must define a message handler to this message. Put this definition on the private section of the main form:

procedure WMQueryEndSession(var Msg : TWMQueryEndSession); message WM_QueryEndSession;

And put this method in the implementation section of the unit:

procedure TForm1.WMQueryEndSession(var Msg : TWMQueryEndSession);

begin

  if MessageDlg('Close Windows ?', mtConfirmation, [mbYes,mbNo], 0) = mrNo then

    Msg.Result := 0

  else

    Msg.Result := 1;

end;