Attaches the menu to the widget and provides a callback function
that will be invoked when the menu calls Menu.detach during
its destruction.
If the menu is attached to the widget then it will be destroyed
when the widget is destroyed, as if it was a child widget.
An attached menu will also move between screens correctly if the
widgets moves between screens.
Attaches the menu to the widget and provides a callback function that will be invoked when the menu calls Menu.detach during its destruction.
If the menu is attached to the widget then it will be destroyed when the widget is destroyed, as if it was a child widget. An attached menu will also move between screens correctly if the widgets moves between screens.