PSBNavigationController.swift

import UIKit

/// Navigation Controller that forwards `prefersStatusBarHidden` and `preferredStatusBarStyle` properties from `topViewController`.
class PSBNavigationController: UINavigationController {
    
    override var viewControllers: [UIViewController] {
        didSet {
            setNeedsStatusBarAppearanceUpdate()
        }
    }
        
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let changeHandler: (_KeyValueCodingAndObserving, NSKeyValueObservedChange<Bool>) -> Void = { [weak self] _, _ in
            self?.setNeedsStatusBarAppearanceUpdate()
        }
        _ = observe(\.navigationBar.isTranslucent, changeHandler: changeHandler)
        _ = observe(\.navigationBar.isHidden, changeHandler: changeHandler)
    }
    
    override var childForStatusBarStyle: UIViewController? {
        if navigationBar.isHidden || navigationBar.isTranslucent {
            return topViewController
        } else {
            return super.childForStatusBarStyle
        }
    }
    
    override var childForStatusBarHidden: UIViewController? {
        topViewController
    }

}