Where is the occurrence "start" date in Ical.Net recurring event?

Question

I am using the nuget package Ical.Net 4.2.0 in my C# project. I've created a recurring calendar event and need to identify the start DateTime for each occurrence. I query the calendar with GetOccurrences() like this:

var now = DateTime.Parse("2021-09-16T10:00:00");
var later = now.AddHours(1);

//Repeat daily for 5 days
var rrule = new RecurrencePattern(FrequencyType.Daily, 1) { Count = 5 };

var e = new CalendarEvent
{
    Start = new CalDateTime(now),
    End = new CalDateTime(later),
    RecurrenceRules = new List<RecurrencePattern> { rrule },
};

var calendar = new Calendar();
calendar.Events.Add(e);

var startSearch = new CalDateTime(DateTime.Parse("2021-09-16T00:00:00"));
var endSearch = new CalDateTime(DateTime.Parse("2021-09-21T23:59:59"));
var occurrences = calendar.GetOccurrences(startSearch, endSearch)
    .Select(o => o.Source)
    .Cast<CalendarEvent>()
    .ToList();

occurrences contains five events, but looking for the "start" date, I can only find the event start date. Where can I find the start dates for each occurrence of a recurring event?

Answer 1

You get them in the actual Occurrence object returned by GetOcurrences (which you are discarding and actually selecting the source CalendarEvent, which is the same for all occurrences), in the Period.StartTime property (which is an IDateTime, which you can convert to .NET datetime objects)

To get all start date times (as DateTimeOffset object):

var startTimes = calendar.GetOccurrences(startSearch, endSearch)
                             .Select(x => x.Period.StartTime.AsDateTimeOffset);

See it in action

Answer 2

You can try with RecurrencePatternEvaluator

var vEvent = new Event {
 DtStart = new CalDateTime(newDateTime(2017, 3, 1, 9, 0, 0)),
 DtEnd = new CalDateTime(newDateTime(2017, 3, 1, 10, 0, 0))
};
var recurrenceRule = new RecurrencePattern(FrequencyDayType.Weekly, 1) {
 ByDay = new IList<IWeekday> { new WeekDay(DayOfWeek.Thursday) }
};
var recurrenceEvaluator = new RecurrencePatternEvaluator(recurrenceRule);
var searchStart = new DateTime(2017, 3, 1, 0, 0, 0);
var searchEnd = new DateTime(2017, 3, 17, 0, 0, 0);
var correctOccurrences = recurrenceEvaluator.Evaluate(vEvent.DtStart, searchStart, searchEnd, false);