A simple extension for handling keyboard shows/hides

KeyboardListener.swift

//
//  KeyboardListener.swift
//
//  Created by Patrick B. Gibson on 7/16/16.
//

import UIKit

protocol KeyboardListener: AnyObject {
    var view: UIView! { get }
    
    // The constraint in your view controller which controls the height of the view the underneath the keyboard.
    var topViewHeightConstraint: NSLayoutConstraint! { get }
}

extension KeyboardListener {
    
    // Called from viewDidLoad to set things up
    func addKeyboardObservers() {
        NSNotificationCenter.defaultCenter().addObserverForName(UIKeyboardWillShowNotification, object: nil, queue: NSOperationQueue.mainQueue(), usingBlock: keyboardWillShow)
        NSNotificationCenter.defaultCenter().addObserverForName(UIKeyboardDidShowNotification, object: nil, queue: NSOperationQueue.mainQueue(), usingBlock: keyboardDidShow)
    }

    func keyboardWillShow(notification: NSNotification) {
        let info = notification.userInfo
        let value = info?[UIKeyboardFrameEndUserInfoKey] as? NSValue
        if let keyboardHeight = value?.CGRectValue().size.height {
            topViewHeightConstraint.constant = view.bounds.height - keyboardHeight
        }
    }
    
    func keyboardDidShow(notification: NSNotification) {
        let info = notification.userInfo
        let value = info?[UIKeyboardFrameEndUserInfoKey] as? NSValue
        if let keyboardHeight = value?.CGRectValue().size.height {
            topViewHeightConstraint.constant = view.bounds.height - keyboardHeight
            UIView.animateWithDuration(0.2, animations: {
                self.view.setNeedsLayout()
                self.view.layoutIfNeeded()
            })
        }
    }
}