在顶层UITableViewController上创建UIButton，就像Airbnb一样

先创建一个按钮，然后重写函数滚动视图DidScroll()：

import UIKit

 class YourTableViewController: UITableViewController {

 private let button = UIButton(type: UIButton.ButtonType.custom) as UIButton

override func viewDidLoad() {
    let image = UIImage(named: "Image.png")
    button.frame = CGRect(x: yourXpos, y: yourYPos, width: 60, height: 60)
    button.setImage(image, for: .normal)
    button.clipsToBounds = true
    button.layer.cornerRadius = 30
    button.addTarget(self, action: #selector(buttonClicked(_:)),    for:.touchUpInside)
    areaOfTableView.addSubview(button)
}

override func scrollViewDidScroll(_ scrollView: UIScrollView) {
    let  offset = self.areaOfTableView.contentOffset.y

   button.frame = CGRect(x: yourXpos, y:   offset + yourYpos, width: btn.frame.size.width, height: btn.frame.size.height)
  }

@objc private func buttonClicked(_ button: UIButton) {
    // Action when you tapped the button
   }

}