How is this implemented in swift 4?

I have this link for a pull down search bar in a table view. I was able to implement the search bar in the tableview with this code

  searchController.searchResultsUpdater = self 
    searchController.obscuresBackgroundDuringPresentation = false
    searchController.searchBar.placeholder = ""
    if #available(iOS 11.0, *) {
        navigationItem.searchController = searchController
    } else {
        self.tableView.tableHeaderView = searchController.searchBar
    }
    definesPresentationContext = true
    searchController.searchBar.delegate = self

I would want to implement the search function now however I am not able to get the text value in the searchbar. Can anyone provide any hints on how to properly implement this? thank you.

EDIT:

This is the viewWillAppear part to hide the searchbar when the view shows up. I have another problem now. If I start to edit the searchbar totally hides from the view. if I remove searchController.searchBar.delegate = self then the searchbar wont hide.

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    self.tableView.contentOffset = CGPoint(x: 0,y :60.0)
}

Instead of setting searchController.searchBar.delegate = self i would recommend to use the UISearchResultsUpdating protocol.

import UIKit

class MyViewController: UIViewController, UISearchResultsUpdating {

    override func viewDidLoad() {
        let searchController = UISearchController(searchResultsController: nil)
        searchController.searchResultsUpdater = self
        searchController.obscuresBackgroundDuringPresentation = false
        searchController.searchBar.placeholder = ""
        searchController.hidesNavigationBarDuringPresentation = false

        if #available(iOS 11.0, *) {
            navigationItem.searchController = searchController
        } else {
            self.tableView.tableHeaderView = searchController.searchBar
        }
        definesPresentationContext = true
        //searchController.searchBar.delegate = self        <--- you don't need this
    }

    func updateSearchResults(for searchController: UISearchController) {
        if let searchString = searchController.searchBar.text {
            print(searchString)
        }
    }
}