Rork Max アプリから予定をカレンダーに登録する — EventKit の権限3段階と書き込み専用アクセスの設計

import SwiftUI
import EventKitUI
 
// 許可不要でシステム標準の予定作成画面を出すラッパー
struct EventEditSheet: UIViewControllerRepresentable {
    let title: String
    let startDate: Date
    let endDate: Date
    let notes: String
    @Environment(\.dismiss) private var dismiss
 
    func makeUIViewController(context: Context) -> EKEventEditViewController {
        let store = EKEventStore()               // 権限リクエストは呼ばない
        let event = EKEvent(eventStore: store)
        event.title = title
        event.startDate = startDate
        event.endDate = endDate
        event.notes = notes
 
        let vc = EKEventEditViewController()
        vc.eventStore = store
        vc.event = event                          // 初期値の事前入力は可能
        vc.editViewDelegate = context.coordinator
        return vc
    }
 
    func updateUIViewController(_ vc: EKEventEditViewController, context: Context) {}
 
    func makeCoordinator() -> Coordinator { Coordinator(dismiss: dismiss) }
 
    final class Coordinator: NSObject, EKEventEditViewDelegate {
        let dismiss: DismissAction
        init(dismiss: DismissAction) { self.dismiss = dismiss }
        func eventEditViewController(_ controller: EKEventEditViewController,
                                     didCompleteWith action: EKEventEditViewAction) {
            dismiss()                             // .saved / .canceled どちらでも閉じる
        }
    }
}

予定詳細画面に「カレンダーに追加」ボタンを追加してください。
実装は EventKitUI の EKEventEditViewController を UIViewControllerRepresentable で
ラップし、sheet で表示する方式にしてください。EKEventStore への
requestFullAccessToEvents / requestWriteOnlyAccessToEvents は呼ばないでください。
Info.plist にカレンダー系の Usage Description キーは追加しないでください。

import EventKit
 
enum CalendarWriter {
    static let store = EKEventStore()
 
    // 書き込み専用アクセスを確認してから予定を保存する
    static func addEvent(title: String, start: Date, end: Date,
                         alarmMinutesBefore: Int? = nil) async throws -> Bool {
        var status = EKEventStore.authorizationStatus(for: .event)
        if status == .notDetermined {
            _ = try await store.requestWriteOnlyAccessToEvents()
            status = EKEventStore.authorizationStatus(for: .event)
        }
        // .writeOnly と .fullAccess のどちらでも書き込みは可能
        guard status == .writeOnly || status == .fullAccess else { return false }
 
        let event = EKEvent(eventStore: store)
        event.title = title
        event.startDate = start
        event.endDate = end
        event.calendar = store.defaultCalendarForNewEvents
        if let minutes = alarmMinutesBefore {
            event.addAlarm(EKAlarm(relativeOffset: TimeInterval(-minutes * 60)))
        }
        try store.save(event, span: .thisEvent)
        return true
    }
}

// フルアクセス前提: 直近7日の予定を取得して重複判定に使う
static func fetchUpcoming(days: Int = 7) async throws -> [EKEvent] {
    guard try await store.requestFullAccessToEvents() else { return [] }
    let start = Date()
    let end = Calendar.current.date(byAdding: .day, value: days, to: start)!
    let predicate = store.predicateForEvents(withStart: start, end: end, calendars: nil)
    return store.events(matching: predicate)
}

// リマインダーはフルアクセスのみ。要求は実際に使う瞬間まで遅延させる
static func addReminder(title: String, due: DateComponents) async throws -> Bool {
    let store = EKEventStore()
    guard try await store.requestFullAccessToReminders() else { return false }
 
    let reminder = EKReminder(eventStore: store)
    reminder.title = title
    reminder.dueDateComponents = due            // 例: 年月日+時分まで指定
    reminder.calendar = store.defaultCalendarForNewReminders()
    reminder.addAlarm(EKAlarm(absoluteDate: Calendar.current.date(from: due)!))
    try store.save(reminder, commit: true)
    return true
}