ios - 向 UINavigationItem 添加按钮根本不起作用

Question

我确信我以前使用过这种模式，但有些东西阻止我将 UIBarButtonItems 添加到我的子类 UINavigationController

// AppDelegate
func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    window = UIWindow(frame: UIScreen.mainScreen().bounds);
    let plainVC = UIViewController();
    plainVC.title = "Plain";
    let explorerNav = ExplorerNavController(rootViewController: plainVC);
    window?.rootViewController = explorerNav;
    window?.makeKeyAndVisible();
    return true
}

//ExplorerNavController
class ExplorerNavController: UINavigationController {

    override func viewDidLoad() {
        super.viewDidLoad()
        self.navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Dumb", style: .Done, target: self, action: #selector(openSettings));
        self.navigationItem.leftBarButtonItem = UIBarButtonItem(barButtonSystemItem: .Done, target: self, action: #selector(openSettings));
    }

    func openSettings(){
        print("did tap open settings");
    }
}

这给我留下了:

我还尝试设置 View Controller 的导航项，在 viewDidAppear 而不是 viewDidLoad 中设置项。我可以在设置导航项时使用相同的 viewDidLoad 设置导航栏的样式，从而证明实际上正在创建 ExplorerNavController 的实例。我只是不确定我错过了什么。

Answer 1

用途:

let leftBarButtonItem = UIBarButtonItem(title: "Dumb", style: .Done, target: self, action: #selector(openSettings))
nav.navigationItem.setLeftBarButtonItem(leftBarButtonItem, animated: true)