Keyboard Handling in UIViewController

KeyboardHandling.swift

import UIKit

private var viewScrollViewAssociatedKey: UInt8 = 0

extension UIViewController {

    var scrollViewInternal: UIScrollView! {
        get {
            return objc_getAssociatedObject(self, &viewScrollViewAssociatedKey) as? UIScrollView
        }
        set(newValue) {
            objc_setAssociatedObject(self, &viewScrollViewAssociatedKey, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }

    // MARK: Keyboard Handling

    func registerKeyboardHandlers(_ scrollView: UIScrollView) {
        self.scrollViewInternal = scrollView

        // Keyboard handler
        NotificationCenter.default.addObserver(
            self,
            selector: #selector(UIViewController.keyboardWillShow(_:)),
            name: NSNotification.Name.UIKeyboardWillShow,
            object: nil
        )

        NotificationCenter.default.addObserver(
            self,
            selector: #selector(UIViewController.keyboardWillHide(_:)),
            name: NSNotification.Name.UIKeyboardWillHide,
            object: nil
        )
    }

    func unregisterKeyboardNotifications() {
        NotificationCenter.default.removeObserver(self)
    }

    internal func keyboardWillShow(_ notification: Foundation.Notification) {
        let userInfo = notification.userInfo
        let value = userInfo?[UIKeyboardFrameEndUserInfoKey] as? NSValue
        let rawFrame = value?.cgRectValue ?? CGRect.zero
        let duration = userInfo?[UIKeyboardAnimationDurationUserInfoKey] ?? 0
        let scrollView = self.scrollViewInternal

        UIView.animate(
            withDuration: (duration as AnyObject).doubleValue,
            delay: 0,
            options: UIViewAnimationOptions(),
            animations: {
                guard let insets = scrollView?.contentInset else { return }
                var newInsets = insets
                newInsets.bottom = rawFrame.height

                scrollView?.contentInset = newInsets
                scrollView?.scrollIndicatorInsets = newInsets
        },
            completion: nil
        )
    }

    internal func keyboardWillHide(_ notification: Foundation.Notification) {
        let userInfo = notification.userInfo
        let duration = userInfo?[UIKeyboardAnimationDurationUserInfoKey] ?? 0
        let scrollView = self.scrollViewInternal

        UIView.animate(
            withDuration: (duration as AnyObject).doubleValue,
            delay: 0,
            options: UIViewAnimationOptions(),
            animations: {
                let insets = UIEdgeInsets.zero
                scrollView?.contentInset = insets
                scrollView?.scrollIndicatorInsets = insets
        },
            completion: nil
        )
    }

}