自定义导航栏不起作用

Question

我正在尝试为整个应用自定义导航栏，但它无法在iOS模拟器中运行。 我使用MasterDetail模板创建了一个项目。

在AppDelegate.swift中

import UIKit 
import CoreData 

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate { 
  var window: UIWindow? 

  func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool { 
    // Override point for customization after application launch 
    let navigationController = self.window!.rootViewController as UINavigationController
    let controller = navigationController.topViewController as MasterViewController
    controller.managedObjectContext = self.managedObjectContext

    var navigationBarAppearance = UINavigationBar.appearance() 
    navigationBarAppearance.tintColor = UIColor.darkGrayColor() 
    navigationBarAppearance.barTintColor = UIColor.whiteColor() 
    if let font = UIFont(name: "Bariol Regular", size: 20) { 
      navigationBarAppearance.titleTextAttributes = [ 
      NSFontAttributeName: font, 
      NSForegroundColorAttributeName: UIColor.whiteColor()] 
    } 
    return true
  }
}