Protocol for observing keyboardWillShow & keyboardWillHide notifications

KeyboardObservable.swift

import UIKit

protocol KeyboardObservable {
    var bottomSpaceToMainViewConstraint: NSLayoutConstraint! { get }
    func subscribeToKeyboardNotifications()
}

extension KeyboardObservable where Self: UIViewController {
    
    func subscribeToKeyboardNotifications() {
        NotificationCenter.default.addObserver(forName: .UIKeyboardWillShow, object: nil, queue: nil) { [weak self] (notification) in
            if let userInfo = notification.userInfo, let keyboardFrame = self?.getKeyboardRect(forKey: UIKeyboardFrameEndUserInfoKey, withUserInfo: userInfo), let values = self?.getDurationAndCurve(fromNotificationUserInfo: userInfo) {
                UIView.animate(withDuration: values.duration, delay: 0, options: UIViewAnimationOptions(rawValue: values.curve), animations: {
                    self?.bottomSpaceToMainViewConstraint.constant = keyboardFrame.size.height
                    self?.view.layoutIfNeeded()
                })
            }
        }
        NotificationCenter.default.addObserver(forName: .UIKeyboardWillHide, object: nil, queue: nil) { [weak self] (notification) in
            if let userInfo = notification.userInfo, let values = self?.getDurationAndCurve(fromNotificationUserInfo: userInfo) {
                UIView.animate(withDuration: values.duration, delay: 0, options: UIViewAnimationOptions(rawValue: values.curve), animations: {
                    self?.bottomSpaceToMainViewConstraint.constant = 0
                    self?.view.layoutIfNeeded()
                })
            }
        }
    }
    
    func getKeyboardRect(forKey key: String, withUserInfo userInfo: [AnyHashable: Any]) -> CGRect? {
        return (userInfo[key] as? NSValue)?.cgRectValue
    }
    
    func getDurationAndCurve(fromNotificationUserInfo userInfo: [AnyHashable: Any]) -> (duration: TimeInterval, curve: UInt)? {
        guard let duration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as? TimeInterval, let curve = userInfo[UIKeyboardAnimationCurveUserInfoKey] as? UInt else {
            return nil
        }
        return (duration, curve)
    }
    
}