如何识别 EKCalendar 以存储用户日历选择

Question

When working with the users calendar, I implemented an EKCalendarChooser which allows the user to select multiple of his calendars. The selected calendar instances are retrieved just fine. Now I later want to use this selection but how can I store it permanently?

My first approach was to use the calendars identifier and store them as a string array to UserDefaults like

@State private var calendarSelection: [EKCalendar]

// my approach to convert the calendar selection into a storable format (string array of ids)
var selectedIds = [String]()
for calendar in calendarSelection {
    selectedIds.append(calendar.calendarIdentifier)
}

// now store the string-array, eg. to user defaults:
UserDefaults.standard.set(selectedIds, forKey: "cids")

Unfortunately this doesn't work, because the calendarIdentifier is not a permanent identifier and thus does change over time. As apple states in their documentation:

A full sync with the calendar will lose this identifier. You should have a plan for dealing with a calendar whose identifier is no longer fetch-able by caching its other properties.

How can the user's selection of his calendars be stored then?

Answer 1

Ok, this works for me now.
I store the calendar identifier ...

func calendarChooserDidFinish(_ calendarChooser: EKCalendarChooser) {
    ...
    // store selected calendar identifier
    selectedCalendar = calendarChooser.selectedCalendars.first?.calendarIdentifier
    ...
}

... then restore it.

func showCalendarChooser() {
    ...
    // check if calendar identifier still exists
    if let selectedCalendarIdentifier = eventStore.calendar(withIdentifier: selectedCalendar) {
        //select stored calendar
        calendarChooser.selectedCalendars = [selectedCalendarIdentifier]
    }
    ...
}

This is for 1 selected calendar only ( selectionStyle: .single ).
Changing this code to multiple calendars should be trivial.

I also tested if the calendar identifier might change ... no joy so far. It remained unchanged during all the tests. If it should change ( nil ), no calendar will be selected and the app won't crash.

HTH

Answer 2

I too have the same problem. The bad thing is you cannot tell when the identifier will change. Here is my work around...

• I store calendar identifier, calendar title, calendar source in userDefaults

• I fetch a set of calendar by comparing identifier first. If identifier is not present in eventStore, then comparing the title AND source.

• Of course, you can add more properties but title + source should be enough in my opinion.

• I have another part in my code that update new identifier in userDefaults.

  if userSettings.selectedCalID != [] { //check if the array is empty or not. If empty then do not use pre-selected calendar.

   var selectedCalendarIdentifier : [EKCalendar] = [] for i in userSettings.selectedCalID{ print(i) if let eventStoreID = eventStore.calendar(withIdentifier: i){ selectedCalendarIdentifier.append(eventStoreID) } else { //This is part where calendar identifier has changed or not present in eventstore. Retrive new identifier by checking calendar title AND calendar source. if userSettings.selectedCalTitle != [] && userSettings.selectedCalSource != [] { let calTitle = userSettings.selectedCalTitle[userSettings.selectedCalID.firstIndex(of: i) ?? 0] let calSource = userSettings.selectedCalSource[userSettings.selectedCalID.firstIndex(of: i) ?? 0] print("\\(calTitle) - \\(calSource)") if let eventStoreCalNewID = eventStore.calendars(for: .event).filter({($0.title == calTitle) && ($0.source.title == calSource)}).first?.calendarIdentifier{ if let eventStoreID = eventStore.calendar(withIdentifier: eventStoreCalNewID){ selectedCalendarIdentifier.append(eventStoreID) } } } } } chooser.selectedCalendars = Set(selectedCalendarIdentifier) }