iOS Done Accessory Bar — The two versions below are mutually exclusive

DoneAccessoryView.swift

import UIKit

class DoneAccessoryView: UIInputView {
    
    private let toolbar = UIToolbar()
    
    init() {
        super.init(frame: .zero, inputViewStyle: .default)
        translatesAutoresizingMaskIntoConstraints = false
        allowsSelfSizing = true
        
        toolbar.translatesAutoresizingMaskIntoConstraints = false
        toolbar.items = [
            UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil),
            UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(dismissKeyboard))
        ]
        addSubview(toolbar)
        
        NSLayoutConstraint.activate([
            toolbar.topAnchor.constraint(equalTo: topAnchor),
            toolbar.leadingAnchor.constraint(equalTo: leadingAnchor),
            bottomAnchor.constraint(equalTo: toolbar.bottomAnchor),
            trailingAnchor.constraint(equalTo: toolbar.trailingAnchor)
        ])
    }
    
    required init?(coder decoder: NSCoder) {
        fatalError()
    }
    
    override func safeAreaInsetsDidChange() {
        super.safeAreaInsetsDidChange()

        toolbar.setNeedsLayout()
    }
    
    @objc private func dismissKeyboard(_ sender: Any) {
        // Left as an exercise to the reader
    }
    
}

DoneAccessoryViewController.swift

import UIKit

class DoneAccessoryViewController: UIInputViewController {
    
    private var toolbar: UIToolbar!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        guard let inputView = inputView else { return }
        inputView.translatesAutoresizingMaskIntoConstraints = false
        inputView.allowsSelfSizing = true
        
        let toolbar = UIToolbar()
        toolbar.translatesAutoresizingMaskIntoConstraints = false
        toolbar.items = [
            UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil),
            UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(dismissKeyboard))
        ]
        inputView.addSubview(toolbar)
        self.toolbar = toolbar
        
        NSLayoutConstraint.activate([
            toolbar.leadingAnchor.constraint(equalTo: inputView.leadingAnchor),
            toolbar.topAnchor.constraint(equalTo: inputView.topAnchor),
            inputView.safeAreaLayoutGuide.bottomAnchor.constraint(equalTo: toolbar.bottomAnchor),
            inputView.trailingAnchor.constraint(equalTo: toolbar.trailingAnchor)
        ])
    }
    
    override func viewSafeAreaInsetsDidChange() {
        super.viewSafeAreaInsetsDidChange()
        
        toolbar.setNeedsLayout()
    }
    
}