User-provided callback function to create a popup for a
GtkMenuButton on demand.
This function is called when the popup of menu_button is shown,
but none has been provided via [methodGtk.MenuButton.set_popover]
or [methodGtk.MenuButton.set_menu_model].
User-provided callback function to create a popup for a
GtkMenuButtonon demand.This function is called when the popup of
menu_buttonis shown, but none has been provided via [methodGtk.MenuButton.set_popover] or [methodGtk.MenuButton.set_menu_model].