It's such a pain to handle the keyboard experience in iOS. Especially when you have bottoms on the button that you will show and so on. Here is a simple Extension that handle's the stuff for you. Start/Stop your observation and provide a bottom constraint for the view that you wanna handle. That's it!

ExampleViewController.swift

//
//  ExampleViewController.swift
//
//  Created by Thomas Paul Mann on 11/06/16.
//  Copyright © 2016 Thomas Paul Mann. All rights reserved.
//

import UIKit

class ExampleViewController: UIViewController {

    // MARK: - Outlets

    @IBOutlet weak var bottomConstraint: NSLayoutConstraint!

    // MARK: - Lifecycle

    override func viewDidLoad() {
        super.viewDidLoad()
    }

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

        startKeyboardObservation()
    }

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

        stopKeyboardObservation()
    }

    // MARK: - Keyboard Observation

    override func bottomConstraint() -> NSLayoutConstraint? {
        return bottomConstraint
    }
    
}

UIViewController+Keyboard.swift

//
//  UIViewController+Keyboard.swift
//
//  Created by Thomas Paul Mann on 12/06/16.
//  Copyright © 2016 Thomas Paul Mann. All rights reserved.
//

import UIKit

extension UIViewController {

    func startKeyboardObservation() {
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(LanguageTranslationViewController.animateWithKeyboard(_:)), name: UIKeyboardWillShowNotification, object: nil)
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(LanguageTranslationViewController.animateWithKeyboard(_:)), name: UIKeyboardWillHideNotification, object: nil)
    }

    func stopKeyboardObservation() {
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }

    // Inspired by this discussion: http://stackoverflow.com/questions/25693130/move-textfield-when-keyboard-appears-swift
    func animateWithKeyboard(notification: NSNotification) {
        guard let
            constraint = bottomConstraint(),
            userInfo = notification.userInfo,
            keyboardHeight = (userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue)?.CGRectValue().height,
            duration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as? Double,
            curve = userInfo[UIKeyboardAnimationCurveUserInfoKey] as? UInt
            else {
                return
        }

        constraint.constant = (notification.name == UIKeyboardWillShowNotification) ? keyboardHeight : 0

        let options = UIViewAnimationOptions(rawValue: curve << 16)

        UIView.animateWithDuration(duration,
                                   delay: 0,
                                   options: options,
                                   animations: { self.view.layoutIfNeeded() },
                                   completion: nil)
    }

    // Override this method to provide your own Constraint
    func bottomConstraint() -> NSLayoutConstraint? {
        return nil
    }

}