activateWindow() doesn't work

[roxton]

Yes, I've tried raise(), and setFocus for the widget, etc - nothing changed, focus stays on the secondary window until I click on the main window.
Now I have found a bad solution:

img_viewer->window.show();
hide();
show();

img_viewer->window.show();
hide();
show();

To copy to clipboard, switch view to plain text mode 

After that, the focus moves to the main window. But I want to move the focus without any window disappearing