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()
    }
}