Presenting SwiftUI View inside UINavigationView and communication between both layers.

SheetHostingViewController.swift

import Combine
import SwiftUI
import UIKit

class SheetHostingViewController: UIViewController {
    @IBOutlet var container: UIView!

    let viewModel = SheetViewModel()
    let alertManager = AlertManager()
    weak var messageHandlerDelegate: SheetMessageHandler?
    var cancellables = Set<AnyCancellable>()

    required init?(coder: NSCoder) {
        super.init(coder: coder)
        setupObservers()
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        let swiftUIView = UIHostingController(rootView: SheetView(viewModel: viewModel))
        addChild(swiftUIView)
        swiftUIView.view.frame = view.bounds
        container.addConstrained(subview: swiftUIView.view)
        swiftUIView.didMove(toParent: self)

        self.title = "Title"
    }

    private func setupObservers() {
        viewModel.showHUD
            .receive(on: DispatchQueue.main)
            .sink { [weak self] value in
                value ? self?.showHUD() : self?.hideHUD()
            }
            .store(in: &cancellables)
        
        viewModel.showErrorAlert
            .receive(on: DispatchQueue.main)
            .sink { [weak self] value in
                guard let self else { return }
                self.present(self.alertManager.loadingError(), animated: true)
            }
            .store(in: &cancellables)

        viewModel.selectedMessage
            .receive(on: DispatchQueue.main)
            .sink { [weak self] message in
                self?.messageHandlerDelegate?.applyMessage(message: message)
                self?.dismiss(animated: true)
            }
            .store(in: &cancellables)
    }
}

extension SheetHostingViewController {
    @IBAction func cancelButton(_ sender: UIBarButtonItem) {
        dismiss(animated: true, completion: nil)
    }
}

// MARK: - Protocol Conformances

// MARK: ProgressHUD Functions
extension SheetHostingViewController: ProgressHUDDisplayable {}

// MAKR: - UIView Extension

extension UIView {
    func addConstrained(subview: UIView) {
        addSubview(subview)
        subview.translatesAutoresizingMaskIntoConstraints = false
        subview.topAnchor.constraint(equalTo: topAnchor).isActive = true
        subview.leadingAnchor.constraint(equalTo: leadingAnchor).isActive = true
        subview.trailingAnchor.constraint(equalTo: trailingAnchor).isActive = true
        subview.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true
    }
}

SheetMessageHandler.swift

protocol SheetMessageHandler: AnyObject {
    func applyMessage(message: String)
}

SheetView.swift

import Combine
import SwiftUI

struct SheetView: View {
    @ObservedObject var viewModel: SheetViewModel
    
    var body: some View {
        VStack(spacing: 0) {
            list
            messageView
        }
        .padding(.bottom, 20)
    }
}

// MARK: Private Views

extension SheetView {
      private var list: some View {
        List($viewModel.results) { item in
            cell(item)    
        }
        .listStyle(.plain)
    }
  
    private var messageView: some View {
        HStack(spacing: 16) {
            TextField("Enter some text", text: $viewModel.message)
                .font(weight: .regular, style: .body)
                .padding(8)
                .overlay(RoundedRectangle(cornerRadius: 10.0).strokeBorder(Color(UIColor.separator), style: StrokeStyle(lineWidth: 1.0)))
                .onReceive(viewModel.message.publisher.collect()) { value in
                    let message = String(value.prefix(200))
                    if viewModel.message != message {
                        viewModel.message = message
                    }
                }
            Button {
                Task {
                    await viewModel.getSuggestedPostText()
                }
            } label: {
                Image("fa_circle-arrow-up")
                    .resizable()
                    .aspectRatio(contentMode: .fit)
                    .frame(maxHeight: 25)
                    .foregroundColor(Color(.accent))
            }
            .disabled(viewModel.message.count <= 0)
        }
        .padding(.horizontal, 20)
    }
}

struct SheetView_Previews: PreviewProvider {
    static var previews: some View {
        SheetView(viewModel: SheetViewModel())
    }
}

SheetViewModel.swift

import Combine
import Foundation

class SheetViewModel: ObservableObject {
    // MARK: Published Variables
    
    @Published var message = ""
    @Published var results: [String] = []
    var selectedMessage = PassthroughSubject<String, Never>()
    
    // MARK: Variables
    
    let showHUD = PassthroughSubject<Bool, Never>()
    let showErrorAlert = PassthroughSubject<Bool, Never>()

    // MARK: Functions
    
    @MainActor
    func getSuggestedPostText() async {
        do {
            showHUD.send(true)
            /// Call API
            showHUD.send(false)
        } catch {
            showHUD.send(false)
            showErrorAlert.send(true)
        }
    }
}

ViewController.swift

class ViewController: UIViewController {
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "SheetHostingViewControllerSegue" {
            let navigationController = segue.destination as? UINavigationController
            if let viewController = navigationController?.viewControllers.first as? SheetHostingViewController {
                viewController.messageHandlerDelegate = self
            }
        }
    }
}


extension ViewController: SheetMessageHandler {
    func applyMessage(message: String) {
        /// Handle Message Selection
    }
}