让我们试试这段代码:

 func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    // Override point for customization after application launch.

    let navigationBarAppearace = UINavigationBar.appearance()
    navigationBarAppearace.tintColor = UIColor.whiteColor()  // Back buttons and such
    navigationBarAppearace.barTintColor = UIColor.purpleColor()  // Bar's background color
    navigationBarAppearace.titleTextAttributes = [NSForegroundColorAttributeName:UIColor.whiteColor()]  // Title's text color

    self.window?.backgroundColor = UIColor.whiteColor()
    return true
}

斯威夫特5.3:

UINavigationBar.appearance().backIndicatorImage = UIImage(named: "custom-back-image")
UINavigationBar.appearance().backIndicatorTransitionMaskImage = UIImage(named: "custom-back-image")

出于某种原因，它在编程上不适合我。但是，在故事板中设置它每次都有效。

如果你试了很多次都没有成功，你可以试试:

UIBarButtonItem.appearance(whenContainedInInstancesOf: [UINavigationBar.self]).tintColor = .red

其实，我试了很多次，才发现这种方法行得通。

我更喜欢自定义NavigationController而不是设置全局ui，或者放在ViewController中。

这是我的解决方案

class AppNavigationController : UINavigationController {

  override func viewDidLoad() {
    super.viewDidLoad()
    self.delegate = self
  }

  override func viewWillAppear(_ animated: Bool) {

  }

}
extension AppNavigationController : UINavigationControllerDelegate {

  func navigationController(_ navigationController: UINavigationController, willShow viewController: UIViewController, animated: Bool) {
    let backButtonItem = UIBarButtonItem(
      title: "   ",
      style: UIBarButtonItem.Style.plain,
      target: nil,
      action: nil)
    backButtonItem.tintColor = UIColor.gray
    viewController.navigationItem.backBarButtonItem = backButtonItem
  }

  func navigationController(_ navigationController: UINavigationController, didShow viewController: UIViewController, animated: Bool) {

  }

}

此外，如果你使用全局设置ui，如UIBarButtonItem.appearance()，你不需要像EKEventEditViewController,PickerViewController等苹果Api。tintColor = .white

在故事板中很容易设置: