Microsoft.Exchange.WebServices.Data.ServiceValidationExcepti

我正在从EWS日历访问约会参与者。我试过了：

cView.PropertySet = new PropertySet(AppointmentSchema.Subject, AppointmentSchema.Start, AppointmentSchema.End);

但我的appointments列表条目中的每个条目都返回了空的Required/Optional Attendees字段，尽管测试预约已经被几个用户接受。我的假设是PropertySet需要包括更多的ApplicationSchema属性，比如：

cView.PropertySet = new PropertySet(AppointmentSchema.Subject,
                AppointmentSchema.Start,
                AppointmentSchema.End,
                AppointmentSchema.RequiredAttendees,
                AppointmentSchema.OptionalAttendees);

但是，这会在日历上引发以下ServiceValidationException错误。FindAppointments（cView）:

Microsoft.Exchange.WebServices.Data.ServiceValidationException：在FindItem请求中不能使用RequiredAdees属性。

如何解决此问题，使appointments包含必需/可选的与会者？

ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2007_SP1);
service.Credentials = new WebCredentials(emailAddress, emailPassword);        
// Initialize values for the start and end times, and the number of appointments to retrieve.
DateTime startDate = DateTime.Now;
DateTime endDate = startDate.AddYears(1);
const int NUM_APPTS = 4;
// Initialize the calendar folder object with only the folder ID. 
CalendarFolder calendar = CalendarFolder.Bind(service, WellKnownFolderName.Calendar, new PropertySet());
// Set the start and end time and number of appointments to retrieve.
CalendarView cView = new CalendarView(startDate, endDate, NUM_APPTS);
// Limit the properties returned to the appointment's subject, start time, and end time.
cView.PropertySet = new PropertySet(AppointmentSchema.Subject,
     AppointmentSchema.Start,
     AppointmentSchema.End,
     AppointmentSchema.RequiredAttendees,
     AppointmentSchema.OptionalAttendees);
// Retrieve a collection of appointments by using the calendar view.
FindItemsResults<Appointment> appointments = calendar.FindAppointments(cView);