KeyboardController handles the most common case of UI update required when the keyboard is presented on iOS. It updates the view's bottom constraint to match the top of the keyboard frame.

KeyboardController.swift

//
//  KeyboardController.swift
//
//  Created by Bruno Guerios on 2017-02-13.
//

import Foundation
import UIKit

class KeyboardController: NSObject {
    
    var viewController: UIViewController
    var constraint: NSLayoutConstraint
    var isKeyboardHidden: Bool {
        return constraint.constant == 0
    }
    
    // MARK: Life Cycle
    
    init(viewController: UIViewController, constraint: NSLayoutConstraint) {
        self.viewController = viewController
        self.constraint = constraint
        super.init()
        self.setupKeyboardObservers()
    }
    
    // MARK: Setup
    
    private func setupKeyboardObservers() {
        self.setupKeyboardWillChangeObserver()
        self.setupDismissKeyboardTapGestureRecognizer()
    }
    
    private func setupKeyboardWillChangeObserver() {
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillChange(_:)), name: .UIKeyboardWillChangeFrame, object: nil)
    }
    
    private func setupDismissKeyboardTapGestureRecognizer() {
        let tap = UITapGestureRecognizer(target: self, action: #selector(dismissKeyboard))
        tap.delegate = self
        viewController.view.addGestureRecognizer(tap)
    }
    
    // MARK: Private
    
    func keyboardWillChange(_ notification: Notification) {
        guard let info = notification.userInfo else { return }
        let keyboardFrame: CGRect = (info[UIKeyboardFrameEndUserInfoKey] as! NSValue).cgRectValue
        constraint.constant = UIScreen.main.bounds.size.height - keyboardFrame.origin.y
        let duration = info[UIKeyboardAnimationDurationUserInfoKey] as! TimeInterval
        UIView.animate(withDuration: duration, animations: {
            self.viewController.view.layoutIfNeeded()
        })
    }
    
    func dismissKeyboard() {
        viewController.view.endEditing(true)
    }
    
}

extension KeyboardController: UIGestureRecognizerDelegate {
    
    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldReceive touch: UITouch) -> Bool {
        return !isKeyboardHidden
    }
    
}