private func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        // Override point for customization after application launch.
        let tabBarViewController = self.window!.rootViewController as! UITabBarController
        var splitViewController:UISplitViewController? = nil
        for viewController in tabBarViewController.viewControllers! {
            splitViewController = viewController as? UISplitViewController
        }
        let navigationController = splitViewController!.viewControllers[splitViewController!.viewControllers.count-1] as! UINavigationController
        navigationController.topViewController!.navigationItem.leftBarButtonItem = splitViewController!.displayModeButtonItem
        splitViewController!.delegate = self
        return true
    }

override func viewDidLoad() {
        super.viewDidLoad()

        self.delegate = self
    }

    func splitViewController(_ splitViewController: UISplitViewController, collapseSecondary secondaryViewController:UIViewController, onto primaryViewController:UIViewController) -> Bool {
        guard let secondaryAsNavController = secondaryViewController as? UINavigationController else { return false }
        guard let topAsDetailController = secondaryAsNavController.topViewController as? DetailViewController else { return false }
        if topAsDetailController.detailItem == nil {
            // Return true to indicate that we have handled the collapse by doing nothing; the secondary controller will be discarded.
            return true
        }
        return false
    }

if let split = self.splitViewController {
            let controllers = split.viewControllers
            self.detailViewController = (controllers[controllers.count-1] as! UINavigationController).topViewController as? DetailViewController
        }