What do u call a person who only notices you or talks to you because of something they want or need from you

People like this are usually referred as "blackholes" people who a person might give attention to but that person that you give attention to don't notice you unless they need you to do something for them.  

huck's relationship with food is a prominent theme throughout the novel, and during his time on jackson's island and working his way down river, huck revels in and enjoys his ad hoc dining. in the first chapter, we observe huck is ironically trapped in a "civilized" world, when he would prefer to live freely in nature.