public protocol LKTabBarButtonView {
    var selected: Bool { get set }
    var index: Int { get set }
    var delegate: LKButtonBarIndexDelegate? { get set }
}

public protocol LKButtonBarIndexDelegate {
    func buttonTapped(index: Int)
    var index: Int { get set }
}

public typealias TabButtonViewPair = (button: LKTabBarButtonView, viewController: UIViewController)

class ButtonView: UIView, LKTabBarButtonView {

    // required elements

    // The button doesn't do anything to set these, just have them available for the tab bar to set up
    // The delegate is set when it is set as a button/view pair in the LKTabBarController's init function
    var delegate: LKButtonBarIndexDelegate?
    // The index is also set up when it is initialized
    var index: Int = 0

    // The actions that can happen when the button's state is changed by the LKTabBarController.
    var selected: Bool = false {
        didSet {
            if selected {
                button.setTitleColor(self.color, forState: .Normal)
                button.enabled = false
                colorBar.backgroundColor = self.color
            } else {
                button.setTitleColor(UIColor.grayColor(), forState: .Normal)
                button.enabled = true
                colorBar.backgroundColor = UIColor.grayColor()
            }
        }
    }

    // user elements    
    @IBAction func buttonTapped() {

        // This is the action that will set the LKTabBarController's index and will change the view
        delegate?.buttonTapped(index)
    }
    ... 
}

let buttonViewPairs: [LKTabBarController.TabButtonViewPair] = []
let viewController = SomeViewController()
let button = ButtonView()

buttonViewPairs.append((button, viewController))

let tabController = LKTabBarController(buttonPairs: buttonViewPairs, parientView: self, containerView: contentView)