setFocus
If @focus is not the current focus widget, and is focusable, sets it as the focus widget for the root.
If @focus is null, unsets the focus widget for the root.
To set the focus to a particular widget in the root, it is usually more convenient to use method@Gtk.Widget.grab_focus instead of this function.
Parameters
focus
widget to be the new focus widget, or null to unset the focus widget