I know - this question is between QT and winapi, but maybe someone have simillar problem. I would like to prevent inactived window. I find solution:
https://stackoverflow.com/questions/5142515/how-can-i-prevent-a-window-from-being-deactivated
( Collin Dauphinee answer )
It is bad solution for me because I can't lose activated for any milisecond ( in this solution I lose active and immediately get it ).

I try:

bool MainWindow::nativeEvent(const QByteArray &eventType, void *message, long *result)
{
  Q_UNUSED(result);
  Q_UNUSED(eventType);

  MSG *msg = static_cast<MSG*>(message);
  if(msg->message == WM_ACTIVATE && msg->wParam==WA_INACTIVE)
  {
     return true;
  }

  return false;
}

But I still lose activate...