SearchViewController.swift

import UIKit

final class SearchViewController: UITableViewController {

    private var searchController: UISearchController!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        searchController = UISearchController(searchResultsController: nil)
        searchController.searchResultsUpdater = self
        searchController.searchBar.sizeToFit()
        
        if #available(iOS 11.0, *) {
            // For iOS 11 and later, we place the search bar in the navigation bar.
            navigationController?.navigationBar.prefersLargeTitles = true
            
            navigationItem.searchController = searchController
            
            // We want the search bar visible all the time.
            navigationItem.hidesSearchBarWhenScrolling = false
        } else {
            // For iOS 10 and earlier, we place the search bar in the table view's header.
            tableView.tableHeaderView = searchController.searchBar
        }
        
        searchController.delegate = self
        searchController.dimsBackgroundDuringPresentation = false // default is YES
        searchController.searchBar.delegate = self    // so we can monitor text changes + others
        
        /*
         Search is now just presenting a view controller. As such, normal view controller
         presentation semantics apply. Namely that presentation will walk up the view controller
         hierarchy until it finds the root view controller or one that defines a presentation context.
         */
        definesPresentationContext = true
    }
}

// MARK: - UISearchResultsUpdating

extension SearchViewController: UISearchResultsUpdating {
    func updateSearchResults(for searchController: UISearchController) {
        guard let text = searchController.searchBar.text else { return }
    }
}

// MARK: - UISearchBarDelegate

extension SearchViewController: UISearchBarDelegate {
    
    func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
        searchBar.resignFirstResponder()
    }
    
    func searchBarCancelButtonClicked(_ searchBar: UISearchBar) {
        searchBar.resignFirstResponder()

    }
}

// MARK: - UISearchControllerDelegate

extension SearchViewController: UISearchControllerDelegate {
    
    func presentSearchController(_ searchController: UISearchController) {
        //debugPrint("UISearchControllerDelegate invoked method: \(__FUNCTION__).")
    }
    
    func willPresentSearchController(_ searchController: UISearchController) {
        //debugPrint("UISearchControllerDelegate invoked method: \(__FUNCTION__).")
    }
    
    func didPresentSearchController(_ searchController: UISearchController) {
        //debugPrint("UISearchControllerDelegate invoked method: \(__FUNCTION__).")
    }
    
    func willDismissSearchController(_ searchController: UISearchController) {
        //debugPrint("UISearchControllerDelegate invoked method: \(__FUNCTION__).")
    }
    
    func didDismissSearchController(_ searchController: UISearchController) {
        //debugPrint("UISearchControllerDelegate invoked method: \(__FUNCTION__).")
    }
}