private string ExportToString(AppAppointment exportApp) { ObservableCollection<AppAppointment> ap = new ObservableCollection<AppAppointment>(); ap.Add(exportApp); StringBuilder builder = new StringBuilder(); using (TextWriter writer = new StringWriter(builder)) { AppointmentCalendarExporter exporter = new AppointmentCalendarExporter(); exporter.Export(ap.OfType<IAppointment>(), writer); } return builder.ToString(); }