Here is what I used previously,
var barButtonItem = UIBarButtonItem(image: backImgs, style: UIBarButtonItemStyle.plain, target: self, action: Selector("menuButtonTapped:"))
But there is some syntax changes for Swift 3.
ex:-
navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Add", style: .plain, target: self, action: #selector(addTapped))