UITabBar.unselectedItemTintColorをiOS9以下でも使えるようにする

UITabBar+.swift

import UIKit

extension UITabBar {

    private struct AssociatedKey {
        static var unselectedItemTintColor = "UITabBar.UnselectedItemTintColor"
    }

    @nonobjc
    var unselectedItemTintColor: UIColor? {
        get {
            return objc_getAssociatedObject(self, &AssociatedKey.unselectedItemTintColor) as? UIColor
        }
        set {
            objc_setAssociatedObject(self, &AssociatedKey.unselectedItemTintColor, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
            
            if let color = newValue {
                setUnselectedItemTintColor(color)
            }
        }
    }

    private func setUnselectedItemTintColor(_ color: UIColor) {
        items?.forEach {
            $0.image = $0.image?.withRenderingMode(.alwaysOriginal)
            $0.setTitleTextAttributes([NSForegroundColorAttributeName: color], for: .normal)
            $0.setTitleTextAttributes([NSForegroundColorAttributeName: tintColor], for: .selected)
        }
    }
}

ViewController.swift

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var tabBar: UITabBar!

    override func viewDidLoad() {
        super.viewDidLoad()
        tabBar.selectedItem = tabBar.items?.first
        tabBar.tintColor = .red
        tabBar.unselectedItemTintColor = .blue
    }
}