KeyboardLayoutGuide

Example.swift

override func viewDidLoad() {
	super.viewDidLoad()

	let keyboardGuide = KeyboardLayoutGuide()
	view.addLayoutGuide(keyboardGuide)

	NSLayoutConstraint.activate([
		someTextField.bottomAnchor.constraint(lessThanOrEqualTo: view.safeAreaLayoutGuide.bottom, constant: -8),
		someTextField.bottomAnchor.constraint(lessThanOrEqualTo: keyboardGuide.topAnchor, constant: -8),
	])
}

KeyboardInfo.swift

import UIKit

public struct KeyboardInfo {

	// MARK: - Properties

	public let frame: CGRect
	public let animationDuration: TimeInterval?
	public let animationOptions: UIView.AnimationOptions?

	// MARK: - Initializers

	init(frame: CGRect) {
		self.frame = frame
		animationDuration = nil
		animationOptions = nil
	}

	init?(notification: Notification) {
		guard let userInfo = notification.userInfo,
			  let frame = userInfo[UIResponder.keyboardFrameEndUserInfoKey] as? CGRect else
		{
			return nil
		}

		self.frame = frame

		animationDuration = userInfo[UIResponder.keyboardAnimationDurationUserInfoKey] as? Double

		let animationCurve = userInfo[UIResponder.keyboardAnimationCurveUserInfoKey] as? UInt
		animationOptions = animationCurve.flatMap { UIView.AnimationOptions(rawValue: $0 << 16) }
	}

	// MARK: - Calculations

	public func height(in view: UIView) -> CGFloat {
		view.frame.intersection(view.convert(frame, from: nil)).height
	}

	// MARK: - Animating

	public func animateAlongsideKeyboard(_ animations: @escaping () -> Void) {
		guard let animationDuration = animationDuration, let animationOptions = animationOptions,
			  animationDuration > 0 else
		{
			animations()
			return
		}

		UIView.animate(withDuration: animationDuration, delay: 0, options: animationOptions, animations: animations)
	}
}

KeyboardLayoutGuide.swift

import Combine
import UIKit

/// Layout guide to automatically track the keyboard.
///
/// - note: If the view changes its frame, you must call `update`.
public final class KeyboardLayoutGuide: UILayoutGuide {

	// MARK: - Properties

	private var constraints = [NSLayoutConstraint]() {
		willSet {
			NSLayoutConstraint.deactivate(constraints)
		}

		didSet {
			NSLayoutConstraint.activate(constraints)
		}
	}

	private var owningViewFrame: CGRect?

	private var subscriptions = Set<AnyCancellable>()

	// MARK: - Initializers

	public override init() {
		super.init()

		identifier = "Keyboard"

		KeyboardManager.shared.$info.sink { [weak self] info in
			self?.update(with: info)
		}.store(in: &subscriptions)

		update()
	}

	@available(*, unavailable)
	required init?(coder: NSCoder) {
		fatalError("init(coder:) has not been implemented")
	}

	// MARK: - UILayoutConstraint

	public override var owningView: UIView? {
		didSet {
			owningViewFrame = owningView?.frame
			update()
		}
	}

	// MARK: - Updating

	/// Must call this when the `owningView` changes its frame
	public func update() {
		guard let owningView = owningView else {
			return
		}

		if owningView.frame != owningViewFrame {
			owningViewFrame = owningView.frame
			update(with: KeyboardManager.shared.info)
		}
	}

	// MARK: - Private

	private func update(with keyboardInfo: KeyboardInfo?) {
		guard let view = owningView, let info = keyboardInfo else {
			return
		}

		let keyboardFrame = view.convert(info.frame, from: nil)

		constraints = [
			heightAnchor.constraint(equalToConstant: view.frame.intersection(keyboardFrame).height),

			// This assumes the keyboard is full width and at the bottom
			widthAnchor.constraint(equalTo: view.widthAnchor),
			leftAnchor.constraint(equalTo: view.leftAnchor),
			bottomAnchor.constraint(equalTo: view.bottomAnchor),
		]

		info.animateAlongsideKeyboard { [weak view] in
			view?.layoutIfNeeded()
		}
	}
}

KeyboardManager.swift

import Combine
import UIKit

final class KeyboardManager {

	// MARK: - Properties

	static let shared = KeyboardManager()

	@Published private(set) var info: KeyboardInfo?

	// MARK: - Initializers
	
	private init() {
		let center = NotificationCenter.default
		center.publisher(for: UIApplication.keyboardWillChangeFrameNotification)
			.merge(with: center.publisher(for: UIApplication.keyboardDidChangeFrameNotification))
			.map(KeyboardInfo.init)
			.assign(to: &$info)
	}
}

Not sure if you intended to include it, but KeyboardInfo is not defined

@chrisbrandow added!

thanks! Also, I'm sure this is a well worn practice, but I've either forgotten, or never knew this is how you use the animation curve value.

let animationCurve = userInfo[UIResponder.keyboardAnimationCurveUserInfoKey] as? UInt
animationOptions = animationCurve.flatMap { UIView.AnimationOptions(rawValue: $0 << 16) }