Qt 窗口标志设置为 Qt::WindowStaysOnTopHint 但不起作用

Question

I have create a 'flash' window to show an image during the application start-up. The image is displayed, in my derived QMainWindow constructor I set the flags:

setWindowFlags(Qt::CustomizeWindowHint
             | Qt::FramelessWindowHint                   
             | Qt::WindowStaysOnTopHint);

However, when another window is created I am able to drag this new window in-front of the splash window which I don't want. I want the dragged window to be behind the splash window until it is remove.

I search online and what I've set should work but it doesn't. I'm using Qt Creator 4.9.0 Based on Qt 5.12.2

My system is an iMAC (Retina 5K, 27-inch, Late 2015).

[Edit] I used the code below to test and prove the fault I'm having, my application window needs to be modal, but I want the splash window to be always on top.

    #include <QMainWindow>
    #include <QApplication>

    int main(int argc, char ** argv)
    {
       QApplication app(argc, argv);

       QMainWindow * mw = new QMainWindow();
       mw->setWindowFlags(Qt::CustomizeWindowHint | Qt::FramelessWindowHint | Qt::WindowStaysOnTopHint);
       mw->resize(500, 500);
       mw->show();

       QMainWindow * secondWindow = new QMainWindow();
       secondWindow->setWindowModality(Qt::ApplicationModal); // <- This breaks the always on top flag
       secondWindow->resize(500, 500);
       secondWindow->show();
       return app.exec();
    }

I've tried setting both windows to be modal, that doesn't help either.

Answer 1

The following program works for me; does it work for you? (on my Mac, running this program opens an empty gray window that is always in front of all other windows)

#include <QMainWindow>
#include <QApplication>

int main(int argc, char ** argv)
{
   QApplication app(argc, argv);

   QMainWindow * mw = new QMainWindow;
   mw->setWindowFlags(Qt::CustomizeWindowHint | Qt::FramelessWindowHint | Qt::WindowStaysOnTopHint);
   mw->resize(500, 500);
   mw->show();

   QMainWindow * secondWindow = new QMainWindow;
   secondWindow->resize(500, 500);
   secondWindow->show();
   return app.exec();
}

If this program does work for you, then you'll need to figure out how your own program differs from this one; OTOH if this program shows the same misbehavior you are seeing in your own program, then it may be there is a bug in the version of Qt that you are using. (I'm testing with Qt 5.12.2 on a 2018 Mac mini running OS/X 10.14.4, FWIW)