SwiftUI + UIInputViewController

InputHostingViewController.swift

// Based on https://gist.github.com/liamnichols/a2e656ae93a597952b4427bcfa371185
// Add allowsSelfSizing support to support inputViewController custom height
// If you need fully dynamic height, please try https://gist.github.com/hannesoid/74ec9022021835598acf17564ce76a5a
/// `UIInputViewController` subclass that wraps a `UIHostingController` allowing you to embed SwiftUI inside `inputAccessoryViewController` and friends.
fileprivate 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")
    }
    
    class InputView: UIInputView {
        var overrideHeight: CGFloat?
        
        override func systemLayoutSizeFitting(_ targetSize: CGSize) -> CGSize {
            let size = super.systemLayoutSizeFitting(targetSize)
            return CGSize(width: size.width, height: overrideHeight ?? size.height)
        }
    }

    override func loadView() {
        let inputView = InputView()
        inputView.overrideHeight = preferredContentSize.height
        view = inputView
    }
    

    override func viewDidLoad() {
        super.viewDidLoad()
        guard let inputView else { return }
        view.translatesAutoresizingMaskIntoConstraints = false
        inputView.allowsSelfSizing = true
        
        addChild(hostingViewController)
        hostingViewController.loadViewIfNeeded()
        hostingViewController.view.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(hostingViewController.view)

        NSLayoutConstraint.activate([
            view.heightAnchor.constraint(equalToConstant: preferredContentSize.height)
        ])

        
        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
        }
    }
}