Make UIViewControllers automatically aware of the keyboard

KeyboardAware.swift

//
//  UIViewController+KeyboardAware.swift
//
//  Created by Zack Sheppard.
//  Copyright © 2020 Zack Sheppard. All rights reserved.
//  Available under the MIT License
//

import UIKit

/// Conforming to this protocol and calling startAvoidingKeyboard will cause
/// your view to automatically shrink to avoid the keyboard when it comes
/// on screen.
@objc protocol KeyboardAware {
    /// Implement this function for additional animation responses to the keyboard
    func customAnimationForNewKeyboardFrame(_ frame: CGRect)
}

// System static variable for the keyboard - is true if it is currently moving
fileprivate var isKeyboardMoving: Bool = false

/// This extension gives UIViewControllers automatic KeyboardAware ability, if you call startAvoidingKeyboard.
/// Based on idea from https://stackoverflow.com/questions/45399178/
extension UIViewController: KeyboardAware {
    var keyboardIsAnimating: Bool {
        return isKeyboardMoving
    }

    /// This view controller should start resizing itself to avoid the keyboard
    func startAvoidingKeyboard() {
        NotificationCenter.default.addObserver(
            self,
            selector: #selector(handleKeyboardFrameWillChangeNotification(_:)),
            name: UIResponder.keyboardWillChangeFrameNotification,
            object: nil
        )
    }

    /// This view controller should stop resizing itself to avoid the keyboard
    func stopAvoidingKeyboard() {
        NotificationCenter.default.removeObserver(
            self,
            name: UIResponder.keyboardWillChangeFrameNotification,
            object: nil
        )
        self.additionalSafeAreaInsets.bottom = 0
    }

    func customAnimationForNewKeyboardFrame(_ frame: CGRect) {
        // Feel free to override this to add custom handling
    }

    @objc private func handleKeyboardFrameWillChangeNotification(_ notification: Notification) {
        guard let userInfo = notification.userInfo,
            let keyboardFrame = (userInfo[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue else {

            isKeyboardMoving = false
            return
        }

        let keyboardFrameInView = view.convert(keyboardFrame, from: nil)
        let safeAreaFrame = view.safeAreaLayoutGuide.layoutFrame.insetBy(dx: 0, dy: -additionalSafeAreaInsets.bottom)
        let intersection = safeAreaFrame.intersection(keyboardFrameInView)

        let animationDuration: TimeInterval = (notification.userInfo?[UIResponder.keyboardAnimationDurationUserInfoKey] as? NSNumber)?.doubleValue ?? 0
        let animationCurve: UIView.AnimationOptions
        if let animationCurveRawValue = (notification.userInfo?[UIResponder.keyboardAnimationCurveUserInfoKey] as? NSNumber)?.uintValue {
            animationCurve = UIView.AnimationOptions(rawValue: animationCurveRawValue)
        } else {
            animationCurve = UIView.AnimationOptions.curveEaseInOut
        }

        isKeyboardMoving = true

        UIView.animate(withDuration: animationDuration, delay: 0, options: animationCurve, animations: {
            self.additionalSafeAreaInsets.bottom = intersection.height
            self.customAnimationForNewKeyboardFrame(intersection)
            self.view.layoutIfNeeded()
        }, completion: { (_) in
            isKeyboardMoving = false
        })
    }
}