Transition to UISearchController's search bar from UITextField

ViewController.swift

import UIKit

extension UIView {
  func makeConstraintsEqual(to view: UIView) {
    if view.translatesAutoresizingMaskIntoConstraints == true {
      view.translatesAutoresizingMaskIntoConstraints = false
    }
    NSLayoutConstraint.activate([
      self.topAnchor.constraint(equalTo: view.topAnchor),
      self.bottomAnchor.constraint(equalTo: view.bottomAnchor),
      self.leadingAnchor.constraint(equalTo: view.leadingAnchor),
      self.trailingAnchor.constraint(equalTo: view.trailingAnchor)
      ])
  }
}

class PresentationViewController: ViewController<PresentationViewModel>, UISearchBarDelegate, UISearchControllerDelegate, UITextFieldDelegate {

  var searchController: UISearchController!
  var containerView: UIView!
  var textField: UITextField!
  var topConstraint: NSLayoutConstraint!

  override func viewDidLoad() {
    super.viewDidLoad()
    self.title = "Search controller"
    self.view.backgroundColor = .white
    self.automaticallyAdjustsScrollViewInsets = false

    self.containerView = UIView(frame: CGRect.zero)
    self.containerView.translatesAutoresizingMaskIntoConstraints = false
    self.view.addSubview(self.containerView)

    if #available(iOS 11.0, *) {
      self.topConstraint = self.containerView.centerYAnchor.constraint(equalTo: self.view.centerYAnchor)
      NSLayoutConstraint.activate([
        self.containerView.centerXAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.centerXAnchor),
        self.topConstraint,
        self.containerView.widthAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.widthAnchor),
        self.containerView.heightAnchor.constraint(equalToConstant: 56)
        ])
    } else {
      self.topConstraint = self.containerView.centerYAnchor.constraint(equalTo: self.view.centerYAnchor)
      NSLayoutConstraint.activate([
        self.containerView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor),
        self.topConstraint,
        self.containerView.widthAnchor.constraint(equalTo: self.view.widthAnchor),
        self.containerView.heightAnchor.constraint(equalToConstant: 56)
        ])
    }

    self.searchController = UISearchController(searchResultsController: nil)
    self.searchController.delegate = self
    self.definesPresentationContext = true
    self.searchController.searchBar.alpha = 0

    self.containerView.addSubview(self.searchController.searchBar)

    self.textField = UITextField(frame: CGRect.zero)
    self.textField.borderStyle = .roundedRect
    self.textField.delegate = self
    self.textField.translatesAutoresizingMaskIntoConstraints = false
    self.textField.placeholder = "Search"
    self.containerView.addSubview(self.textField)
    self.textField.makeConstraintsEqual(to: self.containerView)
  }

  func textFieldShouldBeginEditing(_ textField: UITextField) -> Bool {
    self.view.removeConstraint(self.topConstraint)
    if #available(iOS 11.0, *) {
      self.topConstraint = self.containerView.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor)
    } else {
      self.topConstraint = self.containerView.topAnchor.constraint(equalTo: self.topLayoutGuide.bottomAnchor)
    }
    self.topConstraint.isActive = true

    self.searchController.searchBar.alpha = 0
    UIView.animate(withDuration: 0.3, animations: {
      self.view.layoutIfNeeded()
      self.textField.alpha = 0
      self.searchController.searchBar.alpha = 1
    }) { (_) in
      self.searchController.isActive = true
    }
    return false
  }

  func didPresentSearchController(_ searchController: UISearchController) {
    searchController.searchBar.becomeFirstResponder()
  }

  func didDismissSearchController(_ searchController: UISearchController) {
    self.view.removeConstraint(self.topConstraint)
    self.topConstraint = self.containerView.topAnchor.constraint(equalTo: self.view.centerYAnchor)
    self.topConstraint.isActive = true

    self.textField.alpha = 0
    UIView.animate(withDuration: 0.3, animations: {
      self.view.layoutIfNeeded()
      self.textField.alpha = 1
      self.searchController.searchBar.alpha = 0
    })
  }
}