A Keyboard helper for your Swift Keyboard troubles.

NYSKeyboardHelper.swift

//
//  NYSKeyboardHelper.swift
//  B-NYS GCV
//
//  Created by Matthias on 18/03/2017.
//  https://gist.github.com/matthiasnys/a9d4ce7d6bd997a2153f4bad77263857#file-nyskeyboardhelper-swift-L6
//  Copyright © 2017 B-NYS. All rights reserved.
//

import UIKit

class NYSKeyboardHelper: NSLayoutConstraint {
	@IBInspectable var extraIndent: CGFloat = 0.0
	private var lastNotification: Notification? = nil
	
	override init() {
		super.init()
		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)
	}
	
	/// This can be called to update the constraint if the view moves (without keyboard appearing/disappearing)
	/// Should be used in a popoverviewcontroller -> viewWillLayoutSubviews
	func update() {
		if let notification = lastNotification {
			keyboardDidChangeVisible(notification: notification)
		}
	}
	
	@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
		}
		
		var animationDuration: TimeInterval = 0.0
		var animationOptions: UIViewAnimationOptions = UIViewAnimationOptions(rawValue: 0)
		var endFrame = CGRect.zero
		
		if let animationCurve = notification.userInfo?[UIKeyboardAnimationCurveUserInfoKey] as? UIViewAnimationCurve {
			animationOptions = UIViewAnimationOptions(rawValue: UInt(animationCurve.rawValue << 16))
		}
		
		if let animationDurationFromUserInfo = notification.userInfo?[UIKeyboardAnimationDurationUserInfoKey] as? TimeInterval {
			animationDuration = animationDurationFromUserInfo
		}
		
		if let endFrameFromUserInfo = notification.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 = UIViewAnimationOptions(rawValue: animationOptions.rawValue | UIViewAnimationOptions.layoutSubviews.rawValue)
		
		lastNotification = notification
		
		UIView.animate(withDuration: animationDuration, delay: 0.0, options: animationOptions, animations: {
			self.constant = keyboardHeight
			firstItem.layoutIfNeeded()
		}, completion: nil)
		
	}
}

Initialise using:
self.view.addConstraint(NYSKeyboardHelper(item: self.view, attribute: .bottom, relatedBy: .equal, toItem: scrollView, attribute: .bottom, multiplier: 1.0, constant: 0.0))

If you use it in a popover, be sure to call update when the frame of your contentview has changed!
So:
-> viewWillLayoutSubview -> Call update on the keyboardhandler