navigationController?.additionalSafeAreaInsets.top = 100 
  // where 100 is the extra space

  @IBAction func sliderSlided(_ sender: Any) {
        let top: CGFloat = (CGFloat(200 * ((sender as? UISlider)?.value ?? 1) - 0.5))
        navigationController?.additionalSafeAreaInsets.top = top
  }

    @IBAction func slider2Slided(_ sender: Any) {
        let top: CGFloat = (CGFloat(100 * ((sender as? UISlider)?.value ?? 1)))
        additionalSafeAreaInsets.top = top
    }

@IBAction func push_nav(_ sender: Any) {
  let navVC = UINavigationController(rootViewController: ViewController())  
  navigationController?.pushViewController(navVC, animated: true)
}

  class NavViewController: UINavigationController {
    override func viewDidLoad() {
    super.viewDidLoad()  
    // we’ll work here in a bit  
  }

import UIKit  class NestedViewController: UIViewController {
  var rootVC: UIViewController  
  weak var rootNavigation: UINavigationController?  
  // 1  
  init(rootNavigation: UINavigationController) {  
    guard let vc = rootNavigation.viewControllers.first else { 
      fatalError(“root has not been initialized”)  
    }  
    self.rootVC = vc  
    self.rootNavigation = rootNavigation  
    super.init(nibName: nil, bundle: nil)  
  }  
  required init?(coder: NSCoder) {  
    fatalError(“init(coder:) has not been implemented”)  
  }  
  override func viewDidLoad() {  
    super.viewDidLoad()  
    // 2  
    let childNavigation = rootNavigation ?? UINavigationController(rootViewController: rootVC)  
    childNavigation.willMove(toParent: self)  
    addChild(childNavigation)  
    childNavigation.view.frame = view.frame  
    view.addSubview(childNavigation.view)  
    childNavigation.didMove(toParent: self)  
    childNavigation.navigationBar.isTranslucent = false  
    // 3  rootVC.navigationItem.leftBarButtonItem = 
    UIBarButtonItem(barButtonSystemItem: .close, target: nil, action: #selector(back))  
  }  
  @IBAction func back() {
    navigationController?.popViewController(animated: true)  
  }  
}

@IBAction func new_nav(_ sender: Any) {
  let cvc = UIStoryboard(name: “Main”, bundle: nil).instantiateViewController(identifier: “ViewController”)  
  let nestedVC = NestedViewController(rootNavigation: UINavigationController(rootViewController: cvc))  
  var nav = navigationController  
  while ((nav?.navigationController) != nil) {  
    nav = nav?.navigationController  
  }  
  DispatchQueue.main.async {  
    nestedVC.rootVC.navigationController?.navigationBar.barTintColor = UIColor.random()  
  }  
  nav?.pushViewController(nestedVC, animated: true)  
}

final class AlwaysPoppableDelegate: NSObject, UIGestureRecognizerDelegate {
  weak var navigationController: UINavigationController?  
  weak var originalDelegate: UIGestureRecognizerDelegate?  
  override func responds(to aSelector: Selector!) -> Bool {  
    if aSelector == #selector(gestureRecognizer(_:shouldReceive:)) { 
      return true 
    } else if let responds = originalDelegate?.responds(to: aSelector) {  
      return responds  
    } else {  
      return false  
    }  
  }  
  override func forwardingTarget(for aSelector: Selector!) -> Any? {  
    return originalDelegate  
  }  
  func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldReceive touch: UITouch) -> Bool {  
    return  true  
  }  
}  

protocol Nested {  
  var canNestedSwipeBack: Bool {get set}  
}

private let alwaysPoppableDelegate = AlwaysPoppableDelegate()

setNavigationBarHidden(true, animated: false)  
self.navigationBar.isOpaque = true  
alwaysPoppableDelegate.navigationController = self  
interactivePopGestureRecognizer?.delegate = alwaysPoppableDelegate

func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldReceive touch: UITouch) -> Bool {  
  if let nav = navigationController, nav.isNavigationBarHidden, nav.viewControllers.count > 1 {  
    // extra for nested nav viewcontrollers  
    if let nested = (nav.viewControllers.last as? Nested) {  
      return nested.canNestedSwipeBack  
    } else if let nestedVC = (nav.viewControllers.last as? NestedViewController) {  
      return (nestedVC.rootNavigation?.viewControllers.count ?? 0) <= 1  
    }  return true  
  } else if let result = originalDelegate?.gestureRecognizer?(gestureRecognizer, shouldReceive: touch) {  
    return result  
  } else {  
    return false  
  }  
}

@IBAction func same_nav(_ sender: Any) {  
  let cvc = UIStoryboard(name: “Main”, bundle: nil).instantiateViewController(identifier: “ViewController”)  
  navigationController?.pushViewController(cvc, animated: true)  
}

////  ViewController.swift
//import UIKitclass ViewController: UIViewController {    
    @IBOutlet weak var stackView: UIStackView!    
    override func viewDidLoad() {        
    super.viewDidLoad()        
    // Do any additional setup after loading the view.    
  }    
  //1    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
    super.traitCollectionDidChange(previousTraitCollection)                //2        
    if previousTraitCollection?.preferredContentSizeCategory != traitCollection.preferredContentSizeCategory {            
      let contentSize = traitCollection.preferredContentSizeCategory
      if contentSize.isAccessibilityCategory {                
        stackView.axis = .vertical                
        stackView.alignment = .leading                
        stackView.spacing = 2            
      } else {
        stackView.axis = .horizontal                
        stackView.alignment = .center                
        stackView.spacing = 6            
      }      
    }    
  }
}

override func traitCollectionDidChange(_previousTraitCollection:UITraitCollection?)

import UIKitclass SearchTableViewController: UITableViewController {    
  var filterData: [String]!    
  override func viewDidLoad() {        
    super.viewDidLoad()    
  }    
// MARK: - Table view data source    
  override func numberOfSections(in tableView: UITableView) -> Int {    
    return 1   
  }    
  override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {        
    return filterData.count    
  }        
  override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {        
      let cell = UITableViewCell(style: .default, reuseIdentifier: "cell")
      cell.textLabel?.text = filterData[indexPath.row]        
      return cell    
    }    
  }

import UIKitclass ViewController: UIViewController {    
  @IBOutlet weak var searchBar: UISearchBar!        
  /// Search controller to help us with filtering.    
  private var searchController: UISearchController!        
  /// Secondary search results table view.    
  private var resultsTableController: SearchTableViewController!
  override func viewDidLoad() {        
    super.viewDidLoad()                
    resultsTableController = SearchTableViewController()
    resultsTableController.tableView.delegate = self                
    // 1        
    searchController = UISearchController(searchResultsController: resultsTableController)        
    searchController.searchResultsUpdater = self        
    searchController.searchBar.autocapitalizationType = .none
    // replace searchBar with searchController's searchbar
    searchBar.addSubview(searchController.searchBar)
    searchController.delegate = self
    searchController.dimsBackgroundDuringPresentation = false 
    // The default is true.        
    searchController.searchBar.delegate = self 
    // Monitor when the search button is tapped.                
    // set true to make searchbar moves to navigatoion        
    searchController.hidesNavigationBarDuringPresentation = false
    /** Search presents a view controller by applying normal view controller presentation semantics.         This means that the presentation moves up the view controller hierarchy until it finds the root         view controller or one that defines a presentation context.         */
    /** Specify that this view controller determines how the search controller is presented.         The search controller should be presented modally and match the physical size of this view controller.         */
    definesPresentationContext = true            
    }
  }
  // MARK: - UITableViewDelegateextension 
  ViewController: UITableViewDelegate {        
    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {        
      let selectedString: String        
      // 2         
      // Check to see which table view cell was selected.        
      if tableView === resultsTableController.tableView {
      selectedString = resultsTableController.filterData[indexPath.row]
    } else {            
      selectedString = ""        
    }                
    print(selectedString)                
    tableView.deselectRow(at: indexPath, animated: false)    
  }    
}
// MARK: - UISearchBarDelegate
extension ViewController: UISearchBarDelegate {
  func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
    searchBar.resignFirstResponder()
  }
}
// MARK: - UISearchControllerDelegate
// Use these delegate functions for additional control over the search controller.
extension ViewController: UISearchControllerDelegate {
   func presentSearchController(_ searchController: UISearchController) {
    // 3        
    // to move table under searchbar
    resultsTableController.view.frame = CGRect(x: 0, y: searchBar.frame.maxY, width: self.view.frame.width, height: self.view.frame.height - searchBar.frame.maxY)
    debugPrint("UISearchControllerDelegate invoked method: \(#function).")
  }
  func willPresentSearchController(_ searchController: UISearchController) {
    debugPrint("UISearchControllerDelegate invoked method: \(#function).")
  }
  func didPresentSearchController(_ searchController: UISearchController) {
    // to move content to correct location
    resultsTableController.tableView.contentInset = UIEdgeInsets(top: searchBar.frame.size.height, left: 0, bottom: 0, right: 0)
    debugPrint("UISearchControllerDelegate invoked method: \(#function).")
  }
  func willDismissSearchController(_ searchController: UISearchController) {
    debugPrint("UISearchControllerDelegate invoked method: \(#function).")
  }
  func didDismissSearchController(_ searchController: UISearchController) {
    debugPrint("UISearchControllerDelegate invoked method: \(#function).")
  }    
}
// MARK: - UISearchResultsUpdating
extension ViewController: UISearchResultsUpdating {    
  func updateSearchResults(for searchController: UISearchController) {        // Update the filtered array based on the search text.        
  let searchResults = ["abcde","cdefg","efghi","ghijk"]                
  // Strip out all the leading and trailing spaces.        
  let whitespaceCharacterSet = CharacterSet.whitespaces        
  let strippedString =            searchController.searchBar.text!.trimmingCharacters(in: whitespaceCharacterSet)                
  let filteredResults = searchResults.filter { $0.contains(strippedString) }
  // Apply the filtered results to the search results table.        
  if let resultsController = searchController.searchResultsController as? SearchTableViewController {            
  resultsController.filterData = filteredResults            
  resultsController.tableView.reloadData()        
  }    
 }    
}