Fatal error: use of unimplemented initializer in custom navigationcontroller

Question

I'm creating a custom navigation controller. I have something like this:

public class CustomNavigationController: UINavigationController {

    // MARK: - Life Cycle

    override init(rootViewController: UIViewController) {
        super.init(rootViewController: rootViewController)

        delegate = self
    }

    required public init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        delegate = self
    }
}

I wanted to test this out so I created a CustomNavigationController like this:

CustomNavigationController(rootViewController: ViewController())

When I run the app I get this:

fatal error: use of unimplemented initializer 'init(nibName:bundle:)' for class 'TestApp.CustomNavigationController'

I don't see the problem, can anyone help me out?

what is `delegate = self` ? after just deleting that I could run your code without issue — Alaeddine, Jul 12 '16 at 18:08
This is fixed in iOS 13 - the same code does not result in a fatalError — wyu, Dec 06 '19 at 16:52

score 55 · Accepted Answer · answered Jul 12 '16 at 17:06

55

UINavigationController's implementation of init(rootViewController:) probably calls self.init(nibName:bundle:) which you haven't implemented so it throws the error.

You should override init(nibName:bundle) in addition to the initializers you already override. init(nibName:bundle:) is a designated initializer while init(rootViewController:) is a convenience initializer.

answered Jul 12 '16 at 17:06

dan

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3

init(rootViewController:) cannot be a convenience initializer. As stated in the initializer delegation rules (listed in @Jack's answer below), a designated initializer can only call up to another designated initializer. It should be a compiler error if you attempt to call a superclass convenience initializer from a designated subclass initializer. – Cognitio Jan 07 '18 at 05:05
Thanks.. Helps me a lot in my keyboard extension :) – Anjali jariwala Aug 22 '18 at 06:39
2

This crash is suddenly appeared for iOS12 users. Although empty initialiser doesn't make any sense, it fixes that crash. – SoftDesigner Apr 03 '21 at 07:37

score 34 · Answer 2 · answered Jul 21 '17 at 04:15

While using custom navigation controller, we need to use override initproperty of NavigationController as-

class CustomNavigationController: UINavigationController {

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

    }
    override init(rootViewController: UIViewController) {
        super.init(rootViewController: rootViewController)
    }
    override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
        super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
    }

}

& in Appdelegate class use -

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        self.window = UIWindow(frame: UIScreen.main.bounds)
        let vc = ViewController(nibName: "ViewController", bundle: nil)
        let navi =  CustomNavigationController(rootViewController: vc)
        window?.backgroundColor = .white
        window?.rootViewController = navi
        window?.makeKeyAndVisible()
        return true
    }
}

As per Apple Document - To simplify the relationships between designated and convenience initializers, Swift applies the following three rules for delegation calls between initializers:

Rule 1 A designated initializer must call a designated initializer from its immediate superclass.

Rule 2 A convenience initializer must call another initializer from the same class.

Rule 3 A convenience initializer must ultimately call a designated initializer.

A simple way to remember this is:-

Repose · Answer 3 · 2020-07-13T23:06:49.607

12

I had this issue happen to users on iOS 12.4, so to do a workaround in my custom initializer I did something like this:

init(rootViewController: UIViewController, numberOfPages: Int) {
    self.numberOfPages = numberOfPages
    if #available(iOS 13.0, *) {
        super.init(rootViewController: rootViewController)
    } else {
        super.init(nibName: nil, bundle: nil)
        self.viewControllers = [rootViewController]
    }
}

I basically initialize my class differently for every iOS version below 13. This does seem like the shortest solution.

edited Jul 13 '20 at 23:06

answered Jul 13 '20 at 20:05

Repose

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This solution works well if your subclass has properties needs to be initialized before calling `super.init(nibName: nil, bundle: nil)` – Honghao Z Jul 31 '21 at 20:05

Fatal error: use of unimplemented initializer in custom navigationcontroller

3 Answers3

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