弹出根视图控制器时无法更新导航栏

Question

I have a UITabBar . In one tab is a UINavigationController . Let's say the 2nd or 3rd UIViewController in the stack has this:

class ChildVC: UIViewController {
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        navigationController?.setNavigationBarHidden(true, animated: false)
    }
    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        navigationController?.setNavigationBarHidden(false, animated: false)
    }
}

If you click the current tab it will popToRootViewController() on the navigation controller. The problem is, in viewWillDisappear(:) of my current tab the navigationController is nil. So the navigationBar remains hidden.

What's the proper way to handle this? Should I just set the navigation bar to visible in the root view controller's viewDidAppear ? That seems hacky.

Answer 1

You should override the viewWillAppear in the rootViewController and setNavigationBarHidden from there. navigationController is nil at viewDidDisappear because it has already been popped off the navigation stack.

Answer 2

If anybody else sees this, I don't know why the reference to self.navigationController gets set to nil before viewWillDisappear when you popToRootViewController() but a workaround I found was just to store your own reference to it.

class ChildVC: UIViewController {
    private weak var navCtrl: UINavigationController?

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        navCtrl = navigationController
        navCtrl?.setNavigationBarHidden(true, animated: false)
    }
    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        navCtrl?.setNavigationBarHidden(false, animated: false)
    }
}