Change size of UIBarButtonItem (image) in Swift 3

Extension for Swift 4.2

Just a different way of implementation the answer provided by anoop4real

However using button type .system allows the global tint to be applied to your icon

Usage:

navigationItem.leftBarButtonItem = UIBarButtonItem.menuButton(self, action: #selector(presentSettings), imageName: "settings")

Implementation:

extension UIBarButtonItem {

    static func menuButton(_ target: Any?, action: Selector, imageName: String) -> UIBarButtonItem {
        let button = UIButton(type: .system)
        button.setImage(UIImage(named: imageName), for: .normal)
        button.addTarget(target, action: action, for: .touchUpInside)

        let menuBarItem = UIBarButtonItem(customView: button)
        menuBarItem.customView?.translatesAutoresizingMaskIntoConstraints = false
        menuBarItem.customView?.heightAnchor.constraint(equalToConstant: 24).isActive = true
        menuBarItem.customView?.widthAnchor.constraint(equalToConstant: 24).isActive = true

        return menuBarItem
    }
}

This is how I did it

iOS 10 and below

func setUpMenuButton(){
    let menuBtn = UIButton(type: .custom)
    menuBtn.frame = CGRect(x: 0.0, y: 0.0, width: 20, height: 20)
    menuBtn.setImage(UIImage(named:"menuIcon"), for: .normal)
    menuBtn.addTarget(self, action: #selector(vc.onMenuButtonPressed(_:)), for: UIControlEvents.touchUpInside)

    let menuBarItem = UIBarButtonItem(customView: menuBtn)
    self.navigationItem.leftBarButtonItem = menuBarItem
}

iOS 11 - Navigation bar come up with Autolayout so frame setting may not work

func setUpMenuButton(){
    let menuBtn = UIButton(type: .custom)
    menuBtn.frame = CGRect(x: 0.0, y: 0.0, width: 20, height: 20)
    menuBtn.setImage(UIImage(named:"menuIcon"), for: .normal)
    menuBtn.addTarget(self, action: #selector(vc.onMenuButtonPressed(_:)), for: UIControlEvents.touchUpInside)

    let menuBarItem = UIBarButtonItem(customView: menuBtn)
    let currWidth = menuBarItem.customView?.widthAnchor.constraint(equalToConstant: 24)
    currWidth?.isActive = true
    let currHeight = menuBarItem.customView?.heightAnchor.constraint(equalToConstant: 24)
    currHeight?.isActive = true
    self.navigationItem.leftBarButtonItem = menuBarItem
}