# EventKit Extended Patterns

Overflow reference for the `eventkit` skill. Contains advanced patterns that exceed the main skill file's scope.

## Contents

- [SwiftUI Calendar Integration](#swiftui-calendar-integration)
- [Advanced Predicate Queries](#advanced-predicate-queries)
- [Batch Operations](#batch-operations)
- [Calendar Management](#calendar-management)
- [Reminder Workflows](#reminder-workflows)
- [EventKitUI in SwiftUI](#eventkitui-in-swiftui)
- [Typed Change Notifications](#typed-change-notifications)

## SwiftUI Calendar Integration

Read event data only after full calendar access. Write-only access can create
events but cannot read calendars or events, including events the app created.
When supporting iOS 16 or earlier, availability-guard iOS 17+ access requests
and use `requestAccess(to:)` only on the older path.

### Observable Event Manager

```swift
import EventKit
import SwiftUI

@Observable
@MainActor
final class CalendarManager {
    let eventStore = EKEventStore()
    var events: [EKEvent] = []
    var authorizationStatus: EKAuthorizationStatus = .notDetermined

    func requestAccess() async {
        do {
            let granted = try await eventStore.requestFullAccessToEvents()
            authorizationStatus = granted ? .fullAccess : .denied
            if granted { fetchThisWeekEvents() }
        } catch {
            authorizationStatus = .denied
        }
    }

    func fetchThisWeekEvents() {
        let calendar = Calendar.current
        let start = calendar.startOfDay(for: Date())
        let end = calendar.date(byAdding: .day, value: 7, to: start)!

        let predicate = eventStore.predicateForEvents(
            withStart: start,
            end: end,
            calendars: nil
        )
        events = eventStore.events(matching: predicate)
            .sorted { $0.startDate < $1.startDate }
    }

    func observeChanges() {
        NotificationCenter.default.addObserver(
            forName: .EKEventStoreChanged,
            object: eventStore,
            queue: .main
        ) { [weak self] _ in
            self?.fetchThisWeekEvents()
        }
    }
}
```

### SwiftUI View with Calendar Events

```swift
struct CalendarEventsView: View {
    @State private var manager = CalendarManager()

    var body: some View {
        List(manager.events, id: \.eventIdentifier) { event in
            VStack(alignment: .leading) {
                Text(event.title)
                    .font(.headline)
                Text(event.startDate, style: .date)
                    .font(.caption)
                    .foregroundStyle(.secondary)
            }
        }
        .task {
            await manager.requestAccess()
            manager.observeChanges()
        }
        .overlay {
            if manager.events.isEmpty {
                ContentUnavailableView(
                    "No Events",
                    systemImage: "calendar",
                    description: Text("No events this week.")
                )
            }
        }
    }
}
```

## Advanced Predicate Queries

Event predicates search at most a four-year span. `events(matching:)` and
`enumerateEvents(matching:using:)` are synchronous and include only committed
events, so commit batched changes before querying and move large reads off the
main actor when needed.

### Events in a Specific Calendar

```swift
func fetchEvents(in calendar: EKCalendar, range: DateInterval) -> [EKEvent] {
    let predicate = eventStore.predicateForEvents(
        withStart: range.start,
        end: range.end,
        calendars: [calendar]
    )
    return eventStore.events(matching: predicate)
}
```

### Completed Reminders in a Date Range

```swift
func fetchCompletedReminders(from start: Date, to end: Date) async -> [EKReminder] {
    let predicate = eventStore.predicateForCompletedReminders(
        withCompletionDateStarting: start,
        ending: end,
        calendars: nil
    )

    return await withCheckedContinuation { continuation in
        eventStore.fetchReminders(matching: predicate) { reminders in
            continuation.resume(returning: reminders ?? [])
        }
    }
}
```

### Enumerating Events Efficiently

For large date ranges, use `enumerateEvents` to process events one at a time
without loading all into memory.

```swift
func processAllEvents(from start: Date, to end: Date) {
    let predicate = eventStore.predicateForEvents(
        withStart: start,
        end: end,
        calendars: nil
    )

    eventStore.enumerateEvents(matching: predicate) { event, stop in
        // Process each event
        if event.title.contains("Cancel") {
            stop.pointee = true // Stop enumeration early
        }
    }
}
```

## Batch Operations

### Creating Multiple Events Efficiently

Use `commit: false` for individual saves, then commit once at the end.

```swift
func createEvents(from entries: [(String, Date, Date)]) throws {
    for (title, start, end) in entries {
        let event = EKEvent(eventStore: eventStore)
        event.title = title
        event.startDate = start
        event.endDate = end
        event.calendar = eventStore.defaultCalendarForNewEvents
        try eventStore.save(event, span: .thisEvent, commit: false)
    }
    try eventStore.commit()
}
```

### Deleting Events in Bulk

```swift
func deleteEvents(_ events: [EKEvent]) throws {
    for event in events {
        try eventStore.remove(event, span: .thisEvent, commit: false)
    }
    try eventStore.commit()
}
```

### Resetting Unsaved Changes

```swift
// Discard all uncommitted changes
eventStore.reset()
```

## Calendar Management

### Creating a Custom Calendar

```swift
func createCalendar(name: String, color: CGColor) throws -> EKCalendar {
    let calendar = EKCalendar(for: .event, eventStore: eventStore)
    calendar.title = name
    calendar.cgColor = color

    // Find a local source (iCloud, local, etc.)
    if let localSource = eventStore.sources.first(where: {
        $0.sourceType == .local
    }) {
        calendar.source = localSource
    } else if let defaultSource = eventStore.defaultCalendarForNewEvents?.source {
        calendar.source = defaultSource
    }

    try eventStore.saveCalendar(calendar, commit: true)
    return calendar
}
```

### Listing Calendars by Type

```swift
// All event calendars
let eventCalendars = eventStore.calendars(for: .event)

// All reminder calendars
let reminderCalendars = eventStore.calendars(for: .reminder)

// Only writable calendars
let writableCalendars = eventCalendars.filter { $0.allowsContentModifications }
```

## Reminder Workflows

### Reminder with Location-Based Alarm

```swift
import CoreLocation
import EventKit

enum CalendarError: Error {
    case remindersAccessRequired
    case missingDefaultReminderList
}

func createLocationReminder(
    title: String,
    latitude: Double,
    longitude: Double
) throws {
    guard EKEventStore.authorizationStatus(for: .reminder) == .fullAccess else {
        throw CalendarError.remindersAccessRequired
    }
    guard let reminderCalendar = eventStore.defaultCalendarForNewReminders() else {
        throw CalendarError.missingDefaultReminderList
    }

    let reminder = EKReminder(eventStore: eventStore)
    reminder.title = title
    reminder.calendar = reminderCalendar

    let location = EKStructuredLocation(title: "Target Location")
    location.geoLocation = CLLocation(latitude: latitude, longitude: longitude)
    location.radius = 200 // meters

    let alarm = EKAlarm(relativeOffset: 0)
    alarm.structuredLocation = location
    alarm.proximity = .enter  // .enter or .leave
    reminder.addAlarm(alarm)

    try eventStore.save(reminder, commit: true)
}
```

If the app uses the person's current location while creating location-based
reminders, add `NSLocationWhenInUseUsageDescription` and request Core Location
authorization in the location layer.

### Reminder with Priority

```swift
let reminder = EKReminder(eventStore: eventStore)
reminder.title = "Important Task"
reminder.priority = 1  // 1-4: High, 5: Medium, 6-9: Low, 0: None
reminder.calendar = eventStore.defaultCalendarForNewReminders()
```

## EventKitUI in SwiftUI

### UIViewControllerRepresentable for Event Editor

```swift
import SwiftUI
import EventKitUI

struct EventEditView: UIViewControllerRepresentable {
    let eventStore: EKEventStore
    @Binding var isPresented: Bool

    func makeUIViewController(context: Context) -> EKEventEditViewController {
        let editor = EKEventEditViewController()
        editor.eventStore = eventStore
        editor.editViewDelegate = context.coordinator
        return editor
    }

    func updateUIViewController(
        _ uiViewController: EKEventEditViewController,
        context: Context
    ) {}

    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }

    class Coordinator: NSObject, EKEventEditViewDelegate {
        let parent: EventEditView

        init(_ parent: EventEditView) {
            self.parent = parent
        }

        func eventEditViewController(
            _ controller: EKEventEditViewController,
            didCompleteWith action: EKEventEditViewAction
        ) {
            parent.isPresented = false
        }
    }
}
```

On iOS 17+, the editor can create events without app calendar authorization. It
runs out of process, so the app cannot inspect the dismissed controller to learn
what the person saved unless the app separately has full access and refetches.

### Usage in SwiftUI

```swift
struct CalendarView: View {
    @State private var showEditor = false
    let eventStore = EKEventStore()

    var body: some View {
        Button("Add Event") { showEditor = true }
            .sheet(isPresented: $showEditor) {
                EventEditView(
                    eventStore: eventStore,
                    isPresented: $showEditor
                )
            }
    }
}
```

## Typed Change Notifications

Use `.EKEventStoreChanged` for broad compatibility. On iOS 26+, the typed
notification message is available when you want Foundation's message API:

```swift
if #available(iOS 26.0, *) {
    let observation = NotificationCenter.default.addObserver(
        of: eventStore,
        for: .changed
    ) { _ in
        fetchThisWeekEvents()
    }
}
```