// Swift 3
// The reason I'm passing a UINavigationController and UINavigationItem as parameters is so
// this method can be abstracted away from the view controller.

func showLogoInNavBar(_ navController: UINavigationController, navItem: UINavigationItem) {

    let banner = UIImage(named: "logo-nav-bar")
    let imageView = UIImageView(image: banner)

    let bannerWidth = navController.navigationBar.frame.size.width
    let bannerHeight = navController.navigationBar.frame.size.height

    let bannerX = bannerWidth / 2 - banner!.size.width / 2
    let bannerY = bannerHeight / 2 - banner!.size.height / 2

    imageView.frame = CGRect(x: bannerX, y: bannerY, width: 180, height: bannerHeight)
    imageView.contentMode = UIViewContentMode.scaleAspectFit

    navItem.titleView = imageView
}


// Call the funtion in viewDidLoad by passing in the navigationController and navigationItem
override func viewDidLoad() {
     super.viewDidLoad()
     showLogoInNavBar(self.navigationController!, navItem: self.navigationItem)
}