当NavigationController设置为false时，iOS导航栏tintColor不会变成白色

我的一个Xcode项目遇到了问题。我试图隐藏IOS应用程序的导航栏，但在时间，载体和电池部分/图标上保留白色调。如果将中的navigationController设置为false，self.navigationController?.navigationBarHidden = false则只能将白色变为白色。将其设置为true时，颜色变为白色，没有问题，但导航栏为彩色。这是我的代码。

import UIKit



class ViewController: UIViewController, UITextFieldDelegate {
    @IBOutlet weak var menuButton:UIBarButtonItem!

    @IBOutlet weak var emailTxt: UITextField!
    @IBOutlet weak var passwordTxt: UITextField!
    @IBOutlet weak var signinBtn: UIButton!
    @IBOutlet weak var signupBtn: UIButton!


    var varView = Int()



    override func viewDidLoad() {


        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        emailTxt.delegate = self

        let theWidth = view.frame.size.width
        let theHeight = view.frame.size.height

        emailTxt.frame = CGRectMake(40, 200, theWidth-80, 30)
        passwordTxt.frame = CGRectMake(40, 240, theWidth-80, 30)

        signinBtn.frame = CGRectMake(theWidth-228, 340, 59, 30)

         signupBtn.frame = CGRectMake(theWidth-228, 390, 59, 30)

        let nav = self.navigationController?.navigationBar
        nav?.barStyle = UIBarStyle.Black
        nav?.tintColor = UIColor.whiteColor()
        nav?.titleTextAttributes = [NSForegroundColorAttributeName: UIColor.whiteColor()]

        self.navigationController?.navigationBarHidden = true








        //maparea


    }



    func textFieldShouldReturn(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        return true;
    }

    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
    //emailTxt.resignFirstResponder()
        self.view.endEditing(true)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


    @IBAction func signInBtn(sender: AnyObject) {

        PFUser.logInWithUsernameInBackground(emailTxt.text!, password: passwordTxt.text!) {
            (user:PFUser?, error:NSError?) -> Void in

            if error == nil {

                print("logIn")
                self.performSegueWithIdentifier("gotoMainVCFromSigninVC", sender: self)

            } else {

                print("error")
            }

        }

    }

     }