AddEventToCalendar.swift

import UIKit
import EventKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        
        let eventStore = EKEventStore()
        
        switch EKEventStore.authorizationStatus(for: .event) {
            
        case .authorized:
            insertEvent(store: eventStore)
        case .denied:
            print("Access Denied")
        case .notDetermined:
            eventStore.requestAccess(to: .event) { [weak self] (grant, error) in
                if grant {
                    self?.insertEvent(store: eventStore)
                } else {
                    print("Access Denied, \(error.debugDescription)")
                }
            }
        default:
            print("Case Default")
        }
        
        
    }

    
    func insertEvent(store: EKEventStore) {
        
        guard let sysCal: EKCalendar = store.defaultCalendarForNewEvents else {
            print("fail to accsee default calendar")
            fatalError("This may not be failure")
        }
            
        let startDate = Date()
        let endDate = startDate.addingTimeInterval(2 * 60 * 60)     // A TimeInterval value is always specified in seconds
        
        let event = EKEvent(eventStore: store)
        event.calendar = sysCal
        event.title = "New Event Title"
        event.startDate = startDate
        event.endDate = endDate
        
        do {
            try store.save(event, span: .thisEvent)
        } catch {
            print("Oh no fail, \(error)")
        }
        
    }

}