更改UIBackButtonItem标题

override var backBarButtonItem: UIBarButtonItem {
    get {
        return UIBarButtonItem(title: "自定义标题", style: .plain, target: nil, action: nil)
    }
}

override func popViewController(animated: Bool) -> UIViewController? {
    let poppedViewController = super.popViewController(animated: animated)
    if let poppedViewController = poppedViewController {
        poppedViewController.navigationItem.backBarButtonItem = UIBarButtonItem(title: "自定义标题", style: .plain, target: nil, action: nil)
    }
    return poppedViewController
}

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if let nextViewController = segue.destination as? UIViewController {
        nextViewController.navigationItem.backBarButtonItem = UIBarButtonItem(title: "自定义标题", style: .plain, target: nil, action: nil)
    }
}