How do I transition/animate color of UINavigationBar?

Question

I have been searching for how to transition/animate the barTintColor of a UINavigationBar for a while now, and I only see different answers. Some use <

Answer 1

You can overwrite the push and pop methods of UINavigationController to set the bar color. I've stored the bar color corresponding to a view controller in its navigation item with a custom subclass of UINavigationItem. The following code works for me in iOS 11 for full and for interactive transitions as well:

import UIKit

class NavigationItem: UINavigationItem {
    @IBInspectable public var barTintColor: UIColor?
}

class NavigationController: UINavigationController, UIGestureRecognizerDelegate {
    func applyTint(_ navigationItem: UINavigationItem?) {
        if let item = navigationItem as? NavigationItem {
            self.navigationBar.barTintColor = item.barTintColor
        }
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        applyTint(self.topViewController?.navigationItem)
        self.interactivePopGestureRecognizer?.delegate = self
    }
    override func pushViewController(_ viewController: UIViewController, animated: Bool) {
        applyTint(viewController.navigationItem)
        super.pushViewController(viewController, animated: animated)
    }

    override func popViewController(animated: Bool) -> UIViewController? {
        let viewController = super.popViewController(animated: animated)

        applyTint(self.topViewController?.navigationItem)
        return viewController
    }

    override func popToViewController(_ viewController: UIViewController, animated: Bool) -> [UIViewController]? {
        let result = super.popToViewController(viewController, animated: animated)

        applyTint(viewController.navigationItem)
        return result
    }

    override func popToRootViewController(animated: Bool) -> [UIViewController]? {
        let result = super.popToRootViewController(animated: animated)

        applyTint(self.topViewController?.navigationItem)
        return result
    }

    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
        return true
    }

    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRequireFailureOf otherGestureRecognizer: UIGestureRecognizer) -> Bool {
        return (otherGestureRecognizer is UIScreenEdgePanGestureRecognizer)
    }
}

Note: The coordination of the color animation is done by the navigation controller