Add Subview To Custom UI Button Class - ios

Question

Objective:
When the user clicks the custom button, a blank UIView should appear covering the button.
I've added my code to a new Swift project which looks like this
import UIKit
class DownloadUIButton: UIButton {
var isDownloading: Bool? = false
func addView() {
let view = UIView(frame: self.frame)
view.backgroundColor = UIColor.white
self.addSubview(view)
}
}
class ViewController : UIViewController, UITableViewDelegate, UITableViewDataSource {
fileprivate let tableView: UITableView = UITableView(frame: CGRect.init(x: 0, y: 0, width: 300, height: 300), style: UITableViewStyle.plain)
override func viewDidLoad() {
self.setupTableView()
}
fileprivate func setupTableView() {
self.tableView.dataSource = self
self.tableView.delegate = self
tableView.backgroundColor = UIColor.white
tableView.isOpaque = true
view.addSubview(self.tableView)
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 1
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = UITableViewCell(style: .default, reuseIdentifier: "CellIdentifier")
let buttonSize = 30
let btn = DownloadUIButton(frame: CGRect(x: 10, y: 10, width: buttonSize, height: buttonSize))
btn.backgroundColor = UIColor.red
btn.addTarget(self, action:#selector(handleDownload(_:)), for: .touchUpInside)
cell.addSubview(btn)
return cell
}
#objc func handleDownload(_ btn: DownloadUIButton) {
btn.addView()
}
}
However, the project gives this error:
2017-10-28 12:55:41.558522+0100 TestProject[21392:1779236] *** Terminating app due to uncaught exception 'CALayerInvalid', reason: 'layer is a part of cycle in its layer tree'

Answer 1

To make a view appear in front of your button, I'd just make them sibling views with the same frame. Have the custom view's isHidden set to true at launch time, and when the button's clicked, set the button's isHidden to true and the custom view's isHidden to false. Alternately, if you actually want the button to be visible behind transparent parts of the custom view, you can use sendSubview(toBack:) to make the button appear behind the custom view.