DemoViewController.swift

import Turbolinks
import UIKit

class DemoViewController: Turbolinks.VisitableViewController {
  lazy var errorView: ErrorView = {
    let view = Bundle.main.loadNibNamed("ErrorView", owner: self, options: nil)!.first as! ErrorView
    view.translatesAutoresizingMaskIntoConstraints = false
    view.retryButton.addTarget(self, action: #selector(retry(_:)), for: .touchUpInside)
    return view
  }()

  func presentError(_ error: Error) {
    errorView.error = error
    view.addSubview(errorView)
    installErrorViewConstraints()
  }

  func installErrorViewConstraints() {
    view.addConstraints(
      NSLayoutConstraint.constraints(
        withVisualFormat: "H:|[view]|", options: [], metrics: nil, views: ["view": errorView]))
    view.addConstraints(
      NSLayoutConstraint.constraints(
        withVisualFormat: "V:|[view]|", options: [], metrics: nil, views: ["view": errorView]))
  }

  @objc func retry(_ sender: AnyObject) {
    errorView.removeFromSuperview()
    reloadVisitable()
  }
}