Embed a SwiftUI view inside a UITextView/UITextField inputAccessoryView to present it above the keyboard

Example.swift

import SwiftUI
import UIKit

class ViewController: UIViewController {
    private lazy var textField: UITextField = {
        let textField = UITextField()
        textField.borderStyle = .roundedRect
        textField.translatesAutoresizingMaskIntoConstraints = false
        textField.setInputAccessoryView(height: 56) {
            ScrollView(.horizontal) {
                HStack(spacing: 8) {
                    Button("Print Message", action: { print("Do Foo!") })
                        .buttonStyle(.borderedProminent)

                    Button("Dismiss", action: { [weak self] in self?.textField.resignFirstResponder() })
                        .buttonStyle(.borderedProminent)
                }
                .padding(.horizontal, 8)
            }
            .frame(maxHeight: .infinity)
            .background(Color.red)
        }
        
        return textField
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(textField)
        NSLayoutConstraint.activate([
            textField.topAnchor.constraint(equalTo: view.topAnchor, constant: 8),
            textField.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 8),
            textField.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -8),
        ])
    }
}

InputHostingViewController.swift

import SwiftUI
import UIKit

private var inputAccessoryViewControllerKey: Void?

extension UIView {
    public override var inputAccessoryViewController: UIInputViewController? {
        get { objc_getAssociatedObject(self, &inputAccessoryViewControllerKey) as? UIInputViewController }
        set { objc_setAssociatedObject(self, &inputAccessoryViewControllerKey, newValue, .OBJC_ASSOCIATION_RETAIN) }
    }

    func setInputAccessoryView<Content: View>(height: CGFloat, @ViewBuilder content: () -> Content) {
        let viewController = InputHostingViewController(rootView: content())
        viewController.preferredContentSize.height = height
        inputAccessoryViewController = viewController
    }
}

/// `UIInputViewController` subclass that wraps a `UIHostingController` allowing you to embed SwiftUI inside `inputAccessoryViewController` and friends.
class InputHostingViewController<Content: View>: UIInputViewController {
    let hostingViewController: UIHostingController<Content>

    init(rootView: Content) {
        self.hostingViewController = UIHostingController(rootView: rootView)
        super.init(nibName: nil, bundle: nil)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        view.translatesAutoresizingMaskIntoConstraints = false

        addChild(hostingViewController)

        hostingViewController.loadViewIfNeeded()
        hostingViewController.view.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(hostingViewController.view)

        NSLayoutConstraint.activate([
            hostingViewController.view.topAnchor.constraint(equalTo: view.topAnchor),
            hostingViewController.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            hostingViewController.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            hostingViewController.view.bottomAnchor.constraint(equalTo: view.bottomAnchor)
        ])

        hostingViewController.didMove(toParent: self)
    }

    override var preferredContentSize: CGSize {
        didSet {
            view.bounds.size.height = preferredContentSize.height
        }
    }
}