A Keyboard helper for your Swift Keyboard troubles.

NYSKeyboardHelper.swift

//
//  NYSKeyboardHelper.swift
//  B-NYS GCV
//
//  Created by Matthias Nys on 18/03/2017.
//  Copyright © 2017 B-NYS. All rights reserved.
//

import UIKit

class NYSKeyboardHelper: NSLayoutConstraint {
    @IBInspectable var extraIndent: CGFloat = 0.0
    
    override init() {
        super.init()
        setup()
    }
	
    override func awakeFromNib() {
        super.awakeFromNib()
		
        setup()
    }
	
    private func setup() {
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardDidChangeVisible(notification:)), name: .UIKeyboardWillHide, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardDidChangeVisible(notification:)), name: .UIKeyboardWillShow, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardDidChangeVisible(notification:)), name: .UIKeyboardDidShow, object: nil)
    }
    
    deinit {
        NotificationCenter.default.removeObserver(self, name: .UIKeyboardWillHide, object: nil)
        NotificationCenter.default.removeObserver(self, name: .UIKeyboardWillShow, object: nil)
        NotificationCenter.default.removeObserver(self, name: .UIKeyboardDidShow, object: nil)
    }
    
    @objc private func keyboardDidChangeVisible(notification: Notification) {
        
        guard let firstItem = self.firstItem as? UIView else {
            print("NYSKEYBOARDHELPER: Fist item needs to be a UIView")
            return
        }
        
        guard let superview = firstItem.superview else {
            print("NYSKEYBOARDHELPER: Fist item needs a superview of the type UIView")
            return
        }
		
        let userInfo = notification.userInfo
		
        var animationDuration: TimeInterval = 0.0
        var animationOptions: UIViewAnimationOptions = []
		
        var endFrame = CGRect.zero
        
        if let animationCurve = userInfo?[UIKeyboardAnimationCurveUserInfoKey] as? UIViewAnimationCurve {
            animationOptions = UIViewAnimationOptions(curve: animationCurve)
        }
        
        if let animationDurationFromUserInfo = userInfo?[UIKeyboardAnimationDurationUserInfoKey] as? TimeInterval {
            animationDuration = animationDurationFromUserInfo
        }
        
        if let endFrameFromUserInfo = userInfo?[UIKeyboardFrameEndUserInfoKey] as? CGRect {
            endFrame = endFrameFromUserInfo
        }
        
        let contentAbsoluteFrame = superview.convert(firstItem.frame, to: nil)  //To nil -> On the Window
        let offset = contentAbsoluteFrame.maxY - endFrame.minY + extraIndent
        let keyboardHeight = max(0, offset)
		
        animationOptions.update(with: .layoutSubviews)
		
        UIView .animate(withDuration: animationDuration, delay: 0.0, options: animationOptions, animations: {
            self.constant = keyboardHeight
            firstItem.layoutIfNeeded()
        }, completion: nil)
		
    }
}

extension UIViewAnimationOptions {
    init(curve: UIViewAnimationCurve) {
        switch curve {
        case .easeIn:
            self = .curveEaseIn
        case .easeOut:
            self = .curveEaseOut
        case .easeInOut:
            self = .curveEaseInOut
        case .linear:
            self = .curveLinear
        }
    }
}

The conversion from UIViewAnimationCurve to UIViewAnimationOptions won't work with iOS Keyboard, since the keyboard is using an undocumented UIViewAnimationCurve value that don't match any value of the UIViewAnimationCurve enum.