Utility protocol helping to simplify handling different keyboard notifications.

KeyboardObserving.swift

import UIKit

@objc protocol KeyboardObserving: class {
    
    @objc optional func handleKeyboardWillShow(notification: Notification, keyboardSize: CGSize)
    @objc optional func handleKeyboardWillHide(notification: Notification, keyboardSize: CGSize)
    
    @objc optional func handleKeyboardWillChangeFrame(notification: Notification, keyboardSize: CGSize)
    @objc optional func handleKeyboardDidChangeFrame(notification: Notification, keyboardSize: CGSize)
    
    @objc optional func handleKeyboardDidShow(notification: Notification, keyboardSize: CGSize)
    @objc optional func handleKeyboardDidHide(notification: Notification, keyboardSize: CGSize)
}

extension KeyboardObserving where Self: UIViewController {
    
    func registerForKeyboardNotifications(from notificationCenter: NotificationCenter = .default) {
        
        notificationCenter.addObserver(forName: UIResponder.keyboardWillShowNotification, object: nil, queue: nil) { [weak self] in
            self?.handleKeyboardNotifications(notification: $0)
        }
        notificationCenter.addObserver(forName: UIResponder.keyboardWillHideNotification, object: nil, queue: nil) { [weak self] in
            self?.handleKeyboardNotifications(notification: $0)
        }
        notificationCenter.addObserver(forName: UIResponder.keyboardWillChangeFrameNotification, object: nil, queue: nil) { [weak self] in
            self?.handleKeyboardNotifications(notification: $0)
        }
        notificationCenter.addObserver(forName: UIResponder.keyboardDidChangeFrameNotification, object: nil, queue: nil) { [weak self] in
            self?.handleKeyboardNotifications(notification: $0)
        }
        notificationCenter.addObserver(forName: UIResponder.keyboardDidShowNotification, object: nil, queue: nil) { [weak self] in
            self?.handleKeyboardNotifications(notification: $0)
        }
        notificationCenter.addObserver(forName: UIResponder.keyboardDidHideNotification, object: nil, queue: nil) { [weak self] in
            self?.handleKeyboardNotifications(notification: $0)
        }
    }
    
    private func handleKeyboardNotifications(notification: Notification) {
        guard let userInfo = notification.userInfo else { return }
        let keyboardScreenEndFrame = (userInfo[UIResponder.keyboardFrameEndUserInfoKey] as! NSValue).cgRectValue
        let keyboardViewEndFrame = view.convert(keyboardScreenEndFrame, from: view.window)
        let keyboardSize = keyboardViewEndFrame.size
        
        switch notification.name {
        case UIResponder.keyboardWillShowNotification:
            handleKeyboardWillShow?(notification: notification, keyboardSize: keyboardSize)
        case UIResponder.keyboardWillHideNotification:
            handleKeyboardWillHide?(notification: notification, keyboardSize: keyboardSize)
        case UIResponder.keyboardWillChangeFrameNotification:
            handleKeyboardWillChangeFrame?(notification: notification, keyboardSize: keyboardSize)
        case UIResponder.keyboardDidChangeFrameNotification:
            handleKeyboardDidChangeFrame?(notification: notification, keyboardSize: keyboardSize)
        case UIResponder.keyboardDidShowNotification:
            handleKeyboardDidShow?(notification: notification, keyboardSize: keyboardSize)
        case UIResponder.keyboardDidHideNotification:
            handleKeyboardDidHide?(notification: notification, keyboardSize: keyboardSize)
        default: break
        }
    }
}