Automatic keyboard appearance handling for UIKit

UIScreenAdjuster.swift

//  UIScreenAdjuster.swift
//  Created by Petr Grigorev

//  This code could be used for automatic keyboard appearance handling.
//  It automatically moves screen whenever a new text editing session from
//  UITextField or UITextView is recognized.
//
//  To start using it, just declare a constant inside your AppDelegate, like:
//
//  private let screenAdjuster = UIScreenAdjuster()


import UserNotifications
import UIKit

class UIScreenAdjuster {
    
    private let animationDuration: TimeInterval = 0.4
    private let safeZoneRatio: CGFloat = 0.2
    
    private var isKeyboardVisible = false
    private var firstResponder: UIView?
    private var topViewController: UIViewController? {
        get {
            
            let keyWindow = UIApplication.shared.windows.filter {$0.isKeyWindow}.first

            if var topController = keyWindow?.rootViewController {
                while let presentedViewController = topController.presentedViewController {
                    topController = presentedViewController
                }
                
                return topController
                
            }
            
            return nil
            
        }
    }
    private var currentOffset: CGFloat = 0.0
    
    @objc private func keyboardWillShow(_ notification: Notification) {
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.01, execute: { [weak self] in
            if let self = self {
                if let vc = self.topViewController, let firstResponder = self.firstResponder, let keyboardSize = (notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue {
                    if let frame = firstResponder.superview?.convert(firstResponder.frame, to: vc.view) {
                        
                        let availableScreenHeight = vc.view.frame.height - keyboardSize.height
                        
                        let minSafeY = availableScreenHeight * self.safeZoneRatio
                        let maxSafeY = availableScreenHeight - availableScreenHeight * self.safeZoneRatio
                        
                        let tempCurrentOffset = self.currentOffset
                        
                        let maxYDifference = frame.maxY - maxSafeY
                        if maxYDifference > 0 {
                            self.currentOffset -= maxYDifference
                        }
                        
                        let minYDifference = minSafeY - frame.minY
                        if minYDifference > 0 {
                            self.currentOffset += minYDifference
                        }
                        
                        self.currentOffset > 0 ? self.currentOffset = 0 : nil
                        self.currentOffset < -keyboardSize.height ? self.currentOffset = -keyboardSize.height : nil
                        
                        UIView.animate(withDuration: self.animationDuration, animations: {
                            
                            for view in vc.view.subviews {
                                view.frame.origin = CGPoint(x: view.frame.origin.x, y: view.frame.origin.y - tempCurrentOffset + self.currentOffset)
                            }
                            
                        })
                        
                        self.isKeyboardVisible = true
                    }
                }
            }
        })
    }
    
    @objc private func keyboardWillHide(_ notification: Notification) {
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.01, execute: { [weak self] in
            if let self = self {
                if let vc = self.topViewController {
                    
                    UIView.animate(withDuration: self.animationDuration, animations: {
                        for view in vc.view.subviews {
                            view.frame.origin = CGPoint(x: view.frame.origin.x, y: view.frame.origin.y - self.currentOffset)
                        }
//                            vc.view.frame.origin = CGPoint(x: 0, y: self.currentOffset)
                    })
                    
                    self.currentOffset = 0
                    
//                    UIView.animate(withDuration: duration, animations: {
//                        vc.view.frame.origin = .zero
//                    })
//
                    self.isKeyboardVisible = false
                }
            }
        })
    }
    
    @objc private func textDidBeginEditing(_ notification: Notification) {
        if let view = notification.object as? UIView {
            firstResponder = view
        }
    }
    
    init() {
        
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow(_:)), name: UIResponder.keyboardWillShowNotification, object: nil)
        
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillHide(_:)), name: UIResponder.keyboardWillHideNotification, object: nil)
        
        NotificationCenter.default.addObserver(self, selector: #selector(textDidBeginEditing(_:)), name: UITextField.textDidBeginEditingNotification, object: nil)
        
        NotificationCenter.default.addObserver(self, selector: #selector(textDidBeginEditing(_:)), name: UITextView.textDidBeginEditingNotification, object: nil)
        
    }
    
}