Calendar - How can I expand the recurrences of a recurring item in ItemAdding event receiver?

Question

When a user add a new recurrence event to a calendar I want to check if any of the recurrences overlap with events already in the calendar. I saw the property Recurrences Data and its XML but I didn't find a way to translate that value to dates I can test against the events dates on the calendar. So, is there a way to expand the recurrences of an event in the ItemAdding event receiver of a calendar?

Edit

I manage to get all recurrencies for the item in the ItemAdded event. This is the code I'm using (some code omitted for brevity):

                DateTime _dtAux = new DateTime(DateTime.Now.Year, DateTime.Now.Month, 1);
                query.ExpandRecurrence = true;

                // Get all events (and all recurrencies)
                query.Query = String.Format(@"<Where>
                                <DateRangesOverlap>
                                    <FieldRef Name='EventDate' />;
                                    <FieldRef Name='EndDate' />
                                    <FieldRef Name='RecurrenceID' />
                                    <Value Type='DateTime'><Year /></Value>
                                </DateRangesOverlap>
                            </Where>");

                query.CalendarDate = _dtAux;

                SPListItemCollection existing_events = calendar.GetItems(query);

                // Loop trough all the recurrencies of the item added (where clause)
                foreach (var itemAdded in existing_events.Cast<SPListItem>().Where(x => Convert.ToInt64(x["ID"]) == properties.ListItemId))
                {
                    if (properties.Cancel)
                    {
                        break;
                    }


                    DateTime _itemAddedStart = DateTime.Parse(itemAdded["EventDate"].ToString(), null, System.Globalization.DateTimeStyles.RoundtripKind);
                    DateTime _itemAddedEnd = DateTime.Parse(itemAdded["EndDate"].ToString(), null, System.Globalization.DateTimeStyles.RoundtripKind);

                    // Loop trough all the itens in the calendar except the item added (where clause)
                    foreach (var item in existing_events.Cast<SPListItem>().Where(x => Convert.ToInt64(x["ID"]) != properties.ListItemId))
                    {
                        DateTime _itemStart = DateTime.Parse(item["EventDate"].ToString(), null, System.Globalization.DateTimeStyles.RoundtripKind);
                        DateTime _itemEnd = DateTime.Parse(item["EndDate"].ToString(), null, System.Globalization.DateTimeStyles.RoundtripKind);

                        // Verify if the dates overlap
                        if (_itemAddedStart < _itemEnd && _itemStart < _itemAddedEnd)
                        {
                            properties.Cancel = true;

                            properties.ErrorMessage += "Não foi possível salvar o agendamento, pois um agendamento já foi feito nesta mesma data. <BR><BR>";

                            properties.ErrorMessage += String.Format("Evento: {0} <BR> Hora de Início: {1} <BR> Hora de Término: {2} <BR><BR>", item["Title"], item["EventDate"], item["EndDate"]);

                            properties.ErrorMessage += "Por favor, volte e escolha uma nova data para o agendamento.";

                            // Delete List item
                            SPListItem itemToDelete = calendar.GetItemById(properties.ListItemId);
                            itemToDelete.Delete();

                            break;
                        }
                    }
                }

Now if I delete the item it continues to appear in the calendar and the properties.ErrorMessage doesn't display. Just after a refresh on the page it goes away (still no message).

Any ideas on how to make the item vanish after beign deleted?

Answer 1

According to this article:

You don’t need to parse this XML yourself to get the actual instances of the recurring event. Instead, you can use the SharePoint object model to expand recurring events during a given month:

It is a very large article, well detailed. So I pasted the link. Hope it will be helpfully.