import UIKit

class ViewController: UIViewController {

    var searchBar: UISearchBar!

    var placeholderWidth: CGFloat!

    override func viewDidLoad() {
        super.viewDidLoad()

        searchBar = UISearchBar()
        view.addSubview(self.searchBar)

        searchBar.placeholder = "placeholder"

        if let textFieldOfSearchBar = searchBar.value(forKey: "searchField") as? UITextField {
            textFieldOfSearchBar.textAlignment = .center
            placeholderWidth = textFieldOfSearchBar.attributedPlaceholder?.size().width
        }

        setupAutoLayout()

    }

    override func viewDidLayoutSubviews() {
        let offSet = UIOffset(horizontal: searchBar.frame.width / 2 - placeholderWidth  , vertical: 0)

        searchBar.setPositionAdjustment(offSet, for: .search)
    }

    private func setupAutoLayout() {
        searchBar.translatesAutoresizingMaskIntoConstraints = false
        searchBar.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
        searchBar.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
        searchBar.topAnchor.constraint(equalTo: view.topAnchor, constant: 50) .isActive = true
        searchBar.heightAnchor.constraint(equalToConstant: 50).isActive = true
    }

}