Animated navigation bar tint color on push and interactive pop

DetailViewController.swift

//
//  DetailViewController.swift
//  TransitionCoordinator
//
//  Created by Rob Nadin on 15/02/2015.
//  Copyright (c) 2015 Rob Nadin. All rights reserved.
//

import UIKit

class DetailViewController: UIViewController {

    private var navigationBar: UINavigationBar!
    private var barTintColor: UIColor!
    private var popGesture: UIGestureRecognizer!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }
    
    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        
        self.transitionCoordinator()?.animateAlongsideTransition({ (context) -> Void in
            self.navigationController?.navigationBar.barTintColor = UIColor.greenColor()
        }, completion: nil)
    }
    
    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        
        navigationBar = navigationController?.navigationBar
        barTintColor = navigationBar.barTintColor
        popGesture = self.navigationController?.interactivePopGestureRecognizer
        popGesture.addTarget(self, action: "handlePopRecognizer:")
    }
    
    deinit {
        popGesture.removeTarget(self, action: "handlePopRecognizer:")
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
    @objc private func handlePopRecognizer(recognizer: UIScreenEdgePanGestureRecognizer) {
        var progress = min(1, max(0, recognizer.translationInView(view).x / view.bounds.width))
        if recognizer.state == .Changed {
            navigationBar.barTintColor = colorForProgress(progress)
        }
    }
    
    private func colorForProgress(progress: CGFloat) -> UIColor? {
        let (red, green, blue) = redGreenBlueForColor(barTintColor)
        let (finalRed, finalGreen, finalBlue) = redGreenBlueForColor(UIColor.blueColor())
        let newRed   = (1 - progress) * red   + progress * finalRed
        let newGreen = (1 - progress) * green + progress * finalGreen
        let newBlue  = (1 - progress) * blue  + progress * finalBlue
        return UIColor(red: newRed, green: newGreen, blue: newBlue, alpha: 1.0)
    }

    private func redGreenBlueForColor(color: UIColor) -> (CGFloat, CGFloat, CGFloat) {
        var red: CGFloat = 0, green: CGFloat = 0 , blue: CGFloat = 0
        color.getRed(&red, green: &green, blue: &blue, alpha: nil)
        return (red, green, blue)
    }
    
}