Example of EventKit/Calendar permission crash

ViewController.swift

/*
  How to reproduce crash:
  1. Toggle switch on, Calendar authorization is requested, grant authorization
  2. Switch to the Settings app, disable Calendar authorization
  3. The app crashes

  Or:
  1. Toggle switch on, Calendar authorization is requested, reject authorization
  2. Toggle the switch on again, an alert is shown that you should authorize in the Settings app
  3. Go to the Settings app, enable Calendar authorization
  4. The app crashes
*/

class ViewController: UIViewController {
    
    @IBOutlet weak var calendarSwitch: UISwitch!

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let status = EKEventStore.authorizationStatus(for: .event)
        calendarSwitch.isOn = status == .authorized
        
        calendarSwitch.addTarget(self, action: #selector(didToggleSwitch), for: .touchUpInside)
    }
    
    @objc func didToggleSwitch() {
        guard calendarSwitch.isOn else { return }
        
        switch EKEventStore.authorizationStatus(for: .event) {
        case .authorized:
            print("Is already authorized")
            
        case .denied, .restricted:
            print("Is not authorized")
            calendarSwitch.isOn = false
            showSettingsAlert()
            
        case .notDetermined:
            requestPermission()
            
        }
    }
    
    func showSettingsAlert() {
        let alert = UIAlertController(title: "Not authorized", message: "You need to enable calendar permissions in the Settings app.", preferredStyle: .alert)
        alert.addAction(UIAlertAction(title: "Go to Settings", style: .default, handler: { _ in
            self.openSettings()
        }))
        alert.addAction(UIAlertAction(title: "Cancel", style: .cancel))
        
        present(alert, animated: true)
    }
    
    func openSettings() {
        let url = URL(string: UIApplicationOpenSettingsURLString)!
        guard UIApplication.shared.canOpenURL(url) else { return }
        UIApplication.shared.open(url, options: [:])
    }
    
    func requestPermission() {
        let store = EKEventStore()
        store.requestAccess(to: .event) { [weak self] (authorized, error) in
            if authorized {
                print("Got authorization")
            } else {
                print("Got no authorization")
                DispatchQueue.main.async {
                    self?.calendarSwitch.isOn = false
                }
            }
            if let error = error {
                print("Got error: \(error)")
            }
        }
    }

}