Dynamically sizing a text entry field in an iOS app, depending on keyboard being shown.

TextEditorSizingDemo.swift

//  Created by Andy Dent on 9/2/22.
//  Copyright © 2022 Touchgram Pty Ltd. All rights reserved.

import Foundation
import UIKit

/// portions showing how the sizing works
class SimpleTextNodeDetailViewController: UIViewController {
    @IBOutlet var labelEntryWidthToOverall: NSLayoutConstraint!
    @IBOutlet var labelEntryWidthToPreview: NSLayoutConstraint!

    // connected to adjust item height when keyboard shown
    @IBOutlet var bottomOutletToAdjust: NSLayoutConstraint!
    var saveOutletOffset: CGFloat {get set}

    override public func viewDidLoad()  {
        super.viewDidLoad()

        // ...
        setupScrollForKeyboard()
        entryWidthConfiguredFor(keyboardShown: false)
    }
    
    // helper ensures only one width constraint active at a time
    private func entryWidthConfiguredFor(keyboardShown: Bool) {
        if keyboardShown {
            NSLayoutConstraint.deactivate([labelEntryWidthToPreview])
            NSLayoutConstraint.activate([labelEntryWidthToOverall])
        } else {
            NSLayoutConstraint.deactivate([labelEntryWidthToOverall])
            NSLayoutConstraint.activate([labelEntryWidthToPreview])
        }
    }

    func setupScrollForKeyboard() {
        saveOutletOffset = bottomOutletToAdjust?.constant ?? 0.0
        // note do NOT try using #selector as you cannot within extensions, this is the closure-based alternative
        let notificationCenter = NotificationCenter.default
        notificationCenter.addObserver(forName: UIResponder.keyboardWillHideNotification, object: nil, queue:nil) {
            [weak self] notification in
            self?.adjustForKeyboardHide()
        }
        notificationCenter.addObserver(forName: UIResponder.keyboardWillChangeFrameNotification, object: nil, queue:nil) {
            [weak self] notification in
            self?.adjustForKeyboardResize(notification:notification)
        }
    }

    func adjustForKeyboardHide() {
        guard let bot = bottomOutletToAdjust else {
            os_log("Unable to adjustForKeyboardHide as no bound outlet", log:tgEnv.logImUI, type:.debug)
            return
        }
        os_log("Keyboard hidden, resetting layout constant", log:tgEnv.logImUI, type:.debug)
        bot.constant = saveOutletOffset
        entryWidthConfiguredFor(keyboardShown: false)
    }

    func adjustForKeyboardResize(notification: Notification) {
        guard let bot = bottomOutletToAdjust else {
            os_log("Unable to adjustForKeyboardResize as no bound outlet", log:tgEnv.logImUI, type:.debug)
            return
        }
        guard let userInfo = notification.userInfo else { return }
        
        // cannot cache keyboard sizes as user may change keyboard types to trigger this
        let keyboardScreenEndFrame = (userInfo[UIResponder.keyboardFrameEndUserInfoKey] as! NSValue).cgRectValue
        let keyboardViewEndFrame = view.convert(keyboardScreenEndFrame, from: view.window)
        os_log("Keyboard resized, updating layout constant", log:tgEnv.logImUI, type:.debug)
        entryWidthConfiguredFor(keyboardShown: true)
        bot.constant = max(keyboardViewEndFrame.height + 4, saveOutletOffset)  // when we are using beyond the normal scrollview adjustment, may have something that's already above the keyboard so don't want to drag it down.
    }
    
    private func entryWidthConfiguredFor(keyboardShown: Bool) {
        if keyboardShown {
            NSLayoutConstraint.deactivate([labelEntryWidthToPreview])
            NSLayoutConstraint.activate([labelEntryWidthToOverall])
        } else {
            NSLayoutConstraint.deactivate([labelEntryWidthToOverall])
            NSLayoutConstraint.activate([labelEntryWidthToPreview])
        }
    }




}