Ios Can'；无法读取UITabBarItem外观上的titleTextAttributes

我正在设计我正在构建的应用程序的样式。我想对选项卡栏应用一些系统范围的样式（字体），然后在某些情况下设置颜色之类的样式。我遇到了两个问题：

在UITabBar实例上使用

setTitleTextAttributes:forState:

设置任何titleTextAttributes时，它会立即忽略在外观代理上设置的任何titleTextAttributes（包括未在实例上设置但在外观代理上设置的键）

为了修复（1），我只是想从外观代理复制titleTextAttributes，然后用我想要应用于实例的任何属性覆盖它们。例如

// AppDelegate
func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    UITabBarItem.appearance().setTitleTextAttributes([
        NSFontAttributeName: UIFont(name: "Lato-Regular", size: 20.0)!
        ], forState: .Normal)
}

// Later on in a ViewController that has a UITabBar
override func viewDidLoad() {
    var attributes = UITabBarItem.appearance().titleTextAttributesForState(state) ?? [NSObject: AnyObject]()

    assert(attributes.count > 0, "Could not read titleTextAttributes set on appearance proxy!")
}

这是最烦人的，因为您可以很好地读取UINavigationBar上的外观代理值

有什么想法吗

// AppDelegate
func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    UITabBarItem.appearance().setTitleTextAttributes([
        NSFontAttributeName: UIFont(name: "Lato-Regular", size: 20.0)!
        ], forState: .Normal)
}

// Later on in a ViewController that has a UITabBar
override func viewDidLoad() {
    var attributes = UITabBarItem.appearance().titleTextAttributesForState(state) ?? [NSObject: AnyObject]()

    assert(attributes.count > 0, "Could not read titleTextAttributes set on appearance proxy!")
}