Attaches the menu to the widget and provides a callback function that will be invoked when the menu calls 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.
| this |
a Menu |
| attach_widget |
the Widget that the menu will be attached to |
| detacher |
the user supplied callback function that will be called when the menu calls detach |