Synchronise tasks from the Reminders app within your iOS app using EventKit.

RemindersSync.swift

import EventKit

class RemindersSync {

  let eventStore = EKEventStore()
  
  var remindersCalendar: EKCalendar? = nil
  var reminders: [EKReminder] = []
  
  /// Requests access to the Reminders app
  func requestRemindersAccess(completion: @escaping (Bool) -> Void) {
    eventStore.requestAccess(to: .reminder) { (granted, error) in
      if let error = error {
        print("EKEventStore request access completed with error: \(error.localizedDescription)")
        completion(granted)
        return
      }
      completion(granted)
    }
  }
  
  /// Creates a new calendar for the Reminders app if there is no calendar yet.
  /// Either it fetches an existing calendar, and set it as the `remindersCalendar` property.
  /// The custom calendar is shown as regular list in the Reminders app.
  func createRemindersCalendar() {
    let calendar = EKCalendar(for: .reminder, eventStore: eventStore)
    calendar.source = eventStore.defaultCalendarForNewReminders()?.source // Use the default store for new reminders
    calendar.title = "My App List" // the title will be used as a list title in the Reminders
    calendar.cgColor = UIColor.systemIndigo.cgColor // the color will be used as a list color in the Reminders
    
    do {
      try eventStore.saveCalendar(calendar, commit: true)
    } catch {
      print("Calendar creation failed with error: \(error.localizedDescription)")
      return
    }
    
    remindersCalendar = calendar
  }
  
  func fetchReminders() {
    guard let remindersCalendar = remindersCalendar else { return }
    
    let predicate = eventStore.predicateForReminders(in: [remindersCalendar]) // Use nil insted of [remindersCalendar] to fetch reminders from the default list
    
    eventStore.fetchReminders(matching: predicate) { results in
      if let results = results {
        self.reminders = results
      }
    }
  }
  
  func createReminder(_ title: String) {
    let reminder = EKReminder(eventStore: eventStore)
    reminder.title = title
    reminder.calendar = remindersCalendar
    
    // You can create a completed task
    // reminder.isCompleted = false 
    
    // You can set a task deadline
    // reminder.dueDateComponents = DateComponents()
    
    do {
      try eventStore.save(reminder, commit: true)
    } catch {
      print("Saving reminder failed with error: \(error.localizedDescription)")
    }
  }
}