键盘出现时快速移动视图-Bug

Question

I am new developing with swift and don't know how to resolve my problem. I have two views. One for signUp and one for signIn. I added the following functions to my viewControllers and everything works fine. When I click on each textField (for password, username) the view moves up when keyboard appears. But when I sign in a user and after that call "Part 2" of my code and the User is signed in, the view changes from my signInView to my signUpView. The problem: after I did the following steps and tab now on my textFields the keyboard don't appear anymore.

Part 1: Code in signInViewController:

var kbHeight: CGFloat!

override func viewDidLoad() {
    super.viewDidLoad()

    textFieldUserName.delegate = self
    txtFieldUserPassword.delegate = self
}

func textFieldShouldReturn(textField: UITextField) -> Bool {
    txtFieldUserPassword.resignFirstResponder()

    return true
}

//viewDidAppear or viewWillAppear?
override func viewDidAppear(animated:Bool) {
    super.viewWillAppear(animated)

    NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillShow:"), name: UIKeyboardWillShowNotification, object: nil)
    NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillHide:"), name: UIKeyboardWillHideNotification, object: nil)
}

override func viewWillDisappear(animated: Bool) {
    super.viewWillDisappear(animated)

    NSNotificationCenter.defaultCenter().removeObserver(self)
}

func keyboardWillShow(notification: NSNotification) {
    if let userInfo = notification.userInfo {
        if let keyboardSize =  (userInfo[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.CGRectValue() {
            kbHeight = keyboardSize.height-50
            self.animateTextField(true)
        }
    }
}

func keyboardWillHide(notification: NSNotification) {
    self.animateTextField(false)
}

func animateTextField(up: Bool) {
    let movement = (up ? -kbHeight : kbHeight)

    UIView.animateWithDuration(0.3, animations: {
        self.view.frame = CGRectOffset(self.view.frame, 0, movement)        //Fatal Error: nil sometimes? - Why?
    })
}

Part 2: Code in signInViewController

do {
        try signup.signUpUser()
        self.showAlert(self)
} catch ...


func showAlert(viewController : UIViewController) -> Void {

    let alertController = UIAlertController(title: "Registrieren erfolgreich", message: "Sie können sich jetzt Anmelden", preferredStyle: .Alert)

    alertController.addAction(UIAlertAction(title: "Anmelden", style: .Default, handler: { (alertAction) -> Void in self.dismissViewControllerAnimated(true, completion: nil) }))

    viewController.presentViewController(alertController, animated: true, completion: nil)

Answer 1

I use this handy solution called TPKeyboardAvoiding in one of my apps: https://github.com/michaeltyson/TPKeyboardAvoiding

With this library you don't need handle this kind of scroll behavior on your app, imagine that you can have other behavior in other VC, and you need to calculate it every time.