Let's make calander event & reminder.

Basic flow about making calander event and reminder in Swift 4.0

let eventStore = EKEventStore()

let reminder = EKReminder(eventStore: eventStore)
reminder.title = "reminder"
reminder.calendar = eventStore.defaultCalendarForNewReminders()

let event = EKEvent(eventStore: eventStore)
event.title = "title"
event.startDate = Date()
event.endDate = Date()
event.addAlarm(EKAlarm(relativeOffset: 0))
event.calendar = eventStore.defaultCalendarForNewEvents

try? eventStore.save(event, span: .thisEvent, commit: true)

Setting event/remider calendar property is very important.

reminder.calendar = eventStore.defaultCalendarForNewReminders()
or
event.calendar = eventStore.defaultCalendarForNewEvents

How to make calander event & reminder.