SwiftUI view wrapper for UIKit that calculates its size

SwiftUIView.swift

import SwiftUI

final class SwiftUIView<Content: View>: UIView {

    private var heightConstraint: NSLayoutConstraint?

    init(content: Content, onSizeChanged: @escaping (CGSize) -> Void) {
        super.init(frame: .zero)

        let sizeReadingContent = content.readSize { [weak self] newSize in
            self?.heightConstraint?.constant = newSize.height
            self?.heightConstraint?.isActive = true
            onSizeChanged(newSize)
        }
        let host = UIHostingController(rootView: sizeReadingContent)
        let hostedView: UIView = host.view
        hostedView.backgroundColor = .clear

        addSubview(hostedView)
        hostedView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            hostedView.leadingAnchor.constraint(equalTo: leadingAnchor),
            hostedView.trailingAnchor.constraint(equalTo: trailingAnchor),
            hostedView.topAnchor.constraint(equalTo: topAnchor),
            hostedView.bottomAnchor.constraint(equalTo: bottomAnchor)
        ])

        self.heightConstraint = hostedView.heightAnchor.constraint(equalToConstant: 0)
    }

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

extension View {
    func readSize(_ onSizeChanged: @MainActor @escaping (CGSize) -> Void) -> some View {
        background {
            GeometryReader { geometry in
                Color.clear.assign(geometry.size, to: onSizeChanged)
            }
        }
    }

    func assign<Value: Equatable>(_ value: @autoclosure () -> Value, to action: @MainActor @escaping (Value) -> Void) -> some View {
        let computedValue = value()
        return task(id: computedValue) {
            await action(computedValue)
        }
    }
}