In Swift 3
I found that the following works - here shown as an array of more than one barButtonItem
let barButtonItem1 = UIBarButtonItem( image: UIImage(named: "myImage")?.withRenderingMode(.alwaysOriginal) , style: .plain ,target: self, action: #selector(yourAction))
let barButtonItem2 = UIBarButtonItem(image: UIImage(named: "myImage")?.withRenderingMode(.alwaysOriginal) , style: .plain, target: self, action: #selector(yourAction))
navigationItem.rightBarButtonItems = [barButtonItem1, barButtonItem2]
This shows x2 barButtons on the rightHandSide.
To shown the left simply change to
navigationItem.leftBarButtonItem = [barButtonItem1, barButtonItem2]