Implementing Weekday Calendar Reminders with Holiday Filtering on iOS

Background

The author needed a reliable alarm that skips Chinese statutory holidays on iOS, but iOS does not allow third‑party apps to add alarms directly to the Clock app, nor does it provide built‑in holiday detection. Using Calendar reminders instead of alarms offers a viable solution.

Implementation

Step 1 – Create a Monday‑to‑Friday recurring event

iOS EventKit provides EKRecurrenceRule to define recurrence patterns. The rule is built to repeat weekly on Monday through Friday.

let monday = EKRecurrenceDayOfWeek(.monday)
let tuesday = EKRecurrenceDayOfWeek(.tuesday)
let wednesday = EKRecurrenceDayOfWeek(.wednesday)
let thursday = EKRecurrenceDayOfWeek(.thursday)
let friday = EKRecurrenceDayOfWeek(.friday)
let rule = EKRecurrenceRule(recurrenceWith: .weekly,
                           interval: 1,
                           daysOfTheWeek: [monday, tuesday, wednesday, thursday, friday],
                           daysOfTheMonth: nil,
                           monthsOfTheYear: nil,
                           weeksOfTheYear: nil,
                           daysOfTheYear: nil,
                           setPositions: nil,
                           end: nil)

Permission handling, calendar creation, and event generation are encapsulated in helper functions:

lazy fileprivate var store = EKEventStore()
func requestEventAuth(_ callback: ((Bool) -> Void)?) {
    store.requestAccess(to: .event) { granted, _ in callback?(granted) }
}

func createNewCalendar() { /* create a dedicated calendar */ }
func generateEvent(_ title: String?, location: String?, notes: String?, timeStr: String?) -> EKEvent { /* set title, dates, alarm, recurrence */ }
func addEvent(title: String?, location: String?, notes: String?, timeStr: String, eventKey: String) { /* request auth, create calendar, avoid duplicates, save */ }

Step 2 – Add statutory‑holiday logic

The holiday‑cn JSON provides an array of objects with name , date and isOffDay . The app downloads this file, parses it, and for each day decides whether to delete an existing reminder (if it is a holiday) or add a make‑up reminder (if it is a workday on a weekend).

func filterHolidayInfo(with title: String?, location: String?, notes: String?, timeStr: String, eventKey: String) {
    guard let url = URL(string: "https://natescarlet.coding.net/p/github/d/holiday-cn/git/raw/master/2021.json") else { return }
    let task = URLSession.shared.dataTask(with: url) { data, _, _ in
        guard let data = data else { return }
        do {
            if let json = try JSONSerialization.jsonObject(with: data) as? [String: Any],
               let days = json["days"] as? [[String: Any]] {
                self.handleHolidayInfo(with: days, title: title, location: location, notes: notes, timeStr: timeStr, eventKey: eventKey)
            }
        } catch { print(error) }
    }
    task.resume()
}

func handleHolidayInfo(with days: [[String: Any]], title: String?, location: String?, notes: String?, timeStr: String, eventKey: String) {
    for day in days {
        guard let dayStr = day["date"] as? String,
              let date = Date.date(from: dayStr, formatterStr: "yyyy-MM-dd"),
              let isOffDay = day["isOffDay"] as? Bool else { continue }
        if date.timeIntervalSinceNow < 0 { continue }
        if let existing = eventExist(on: date, eventKey: eventKey) {
            if isOffDay { try? store.remove(existing, span: .thisEvent) }
        } else if !isOffDay {
            // add make‑up event
            let timePart = timeStr.components(separatedBy: " ").last ?? "00:00:00"
            let targetStr = "\(dayStr) \(timePart)"
            let event = generateEvent(title, location: location, notes: notes, timeStr: targetStr)
            try? store.save(event, span: .thisEvent)
        }
    }
}

Utility functions eventExist and eventExist check for existing events in the custom calendar to avoid duplicates.

Result

After running the code, the calendar shows reminders on every weekday except official holidays, and additional reminders are created for make‑up workdays (e.g., 2021‑09‑18, 2021‑09‑26, 2021‑10‑09). Screenshots confirm the expected behavior.

Conclusion

The approach combines EventKit recurrence rules with dynamic holiday data, offering a flexible way to manage work‑day reminders on iOS. Future improvements could include versioned holiday data from a private server to automatically refresh the calendar when the holiday list changes.