How do you define last week of month in Recurring Rule (ByWeekNumber)

Question

How do you define last week in month for the recurring rule when using ByWeekNumber? In Outlook, they use Last as the designation. So, if I have a recurring rule that is Last Wednesday in the month, how do I describe the rule?

Answer 1

BYWEEKNO (ByWeekNumber) rule part is only valid for YEARLY rules (Frequency.Yearly)

Last Wednesday in the month is:

RRULE:FREQ=MONTHLY;INTERVAL=1;BYDAY=-1WE

The code for that is:

RecurringRule recurring = new RecurringRule();
recurring.Frequency = Frequency.Monthly;
recurring.ByDay.Add(Weekday.LastWednesday);

Creating an email with such rule:

Appointment appointment = new Appointment();
Event e = appointment.AddEvent();
e.SetOrganizer(new Person("Frank From", "from@example.com"));
e.AddParticipant(new Participant("Tom To", "to@example.com"));
e.Description = "Event description";
e.Summary = "Event summary";
e.Start = new DateTime(2014, 11, 26, 9, 0, 0);
e.End = new DateTime(2014, 11, 26, 10, 0, 0);

RecurringRule recurring = e.AddRecurringRule();
recurring.Frequency = Frequency.Monthly;
recurring.ByDay.Add(Weekday.LastWednesday);

Alarm alarm = e.AddAlarm();
alarm.Description = "Reminder";
alarm.BeforeStart(TimeSpan.FromMinutes(5));

var builder = new MailBuilder();
builder.Subject = "with appointment";
builder.From.Add(new MailBox("from@example.com"));
builder.To.Add(new MailBox("to@example.com"));
builder.Text = "Some text. Appointment is attached";
builder.AddAppointment(appointment);
IMail email = builder.Create();