if available – UIRefreshControl

ViewController.swift

import Foundation
import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {    
        super.viewDidLoad()

        let refreshControl = UIRefreshControl()
        refreshControl.addTarget(self, action: #selector(refresh), for: .valueChanged)
        
        if #available(iOS 10.0, *) {
            scrollView.refreshControl = refreshControl
        } else {
            scrollView.alwaysBounceVertical = true
            scrollView.addSubview(refreshControl)
        }
    }

    func refresh(_ refreshControl: UIRefreshControl) {
        refreshControl.endRefreshing()
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
}