A UIViewController subclass that manages shifting the view controller up when editing a UITextField or UITextView that would normally be obscured by they keyboard popping up so that the text input is visible.

ShiftableViewController.swift

//		
//  ShiftableViewController.swift			
//		
//  Copyright © 2020 Spencer Curtis. All rights reserved.		
//		

 /*		
 		
 All you need to do is set your subclass of ShiftableViewController as the delegate for all		
 UITextFields and UITextViews that you want to be shifted up so the keyboard doesn't obscure it.		
 		
 */

import UIKit

class ShiftableViewController: UIViewController, UITextFieldDelegate, UITextViewDelegate, UIGestureRecognizerDelegate {
    
    var currentYShiftForKeyboard: CGFloat = 0
    
    var textFieldBeingEdited: UITextField?
    var textViewBeingEdited: UITextView?
    
    var keyboardDismissTapGestureRecognizer: UITapGestureRecognizer!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        setupKeyboardDismissTapGestureRecognizer()

        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow(notification:)), name: UIResponder.keyboardWillShowNotification, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillHide(notification:)), name: UIResponder.keyboardWillHideNotification, object: nil)
        
    }
    
    @objc func stopEditingTextInput() {
        if let textField = self.textFieldBeingEdited {
            
            textField.resignFirstResponder()
            
            self.textFieldBeingEdited = nil
            self.textViewBeingEdited = nil
        } else if let textView = self.textViewBeingEdited {
            
            textView.resignFirstResponder()
            
            self.textFieldBeingEdited = nil
            self.textViewBeingEdited = nil
        }
        
        guard keyboardDismissTapGestureRecognizer.isEnabled else { return }
        
        keyboardDismissTapGestureRecognizer.isEnabled = false
    }
    
    func textFieldDidBeginEditing(_ textField: UITextField) {
        textFieldBeingEdited = textField
    }
    
    func textViewShouldBeginEditing(_ textView: UITextView) -> Bool {
        textViewBeingEdited = textView
        return true
    }
    
    @objc func keyboardWillShow(notification: Notification) {
        
        keyboardDismissTapGestureRecognizer.isEnabled = true
        
        var keyboardSize: CGRect = .zero
        
        if let keyboardRect = notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? CGRect,
            keyboardRect.height != 0 {
            keyboardSize = keyboardRect
        } else if let keyboardRect = notification.userInfo?["UIKeyboardBoundsUserInfoKey"] as? CGRect {
            keyboardSize = keyboardRect
        }
        
        if let textField = textFieldBeingEdited  {
            if self.view.frame.origin.y == 0 {
                
                let yShift = yShiftWhenKeyboardAppearsFor(textInput: textField, keyboardSize: keyboardSize, nextY: keyboardSize.height)
                self.currentYShiftForKeyboard = yShift
                self.view.frame.origin.y -= yShift
            }
        } else if let textView = textViewBeingEdited {
            if self.view.frame.origin.y == 0 {
                
                let yShift = yShiftWhenKeyboardAppearsFor(textInput: textView, keyboardSize: keyboardSize, nextY: keyboardSize.height)
                self.currentYShiftForKeyboard = yShift
                self.view.frame.origin.y -= yShift
            }
        }
    }
    
    @objc func yShiftWhenKeyboardAppearsFor(textInput: UIView, keyboardSize: CGRect, nextY: CGFloat) -> CGFloat {
        
        let textFieldOrigin = self.view.convert(textInput.frame, from: textInput.superview!).origin.y
        let textFieldBottomY = textFieldOrigin + textInput.frame.size.height
        
        // This is the y point that the textField's bottom can be at before it gets covered by the keyboard
        let maximumY = self.view.frame.height - (keyboardSize.height + view.safeAreaInsets.bottom)
        
        if textFieldBottomY > maximumY {
            // This makes the view shift the right amount to have the text field being edited just above they keyboard if it would have been covered by the keyboard.
            return textFieldBottomY - maximumY
        } else {
            // It would go off the screen if moved, and it won't be obscured by the keyboard.
            return 0
        }
    }
    
    @objc func keyboardWillHide(notification: Notification) {
        
        if self.view.frame.origin.y != 0 {
            
            self.view.frame.origin.y += currentYShiftForKeyboard
        }
        
        stopEditingTextInput()
    }
    
    @objc func setupKeyboardDismissTapGestureRecognizer() {
        
        let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(stopEditingTextInput))
        tapGestureRecognizer.numberOfTapsRequired = 1
        
        view.addGestureRecognizer(tapGestureRecognizer)
        
        keyboardDismissTapGestureRecognizer = tapGestureRecognizer
        
    }
}