public ChangeExecuteDateDialogViewModel(RequestServiceImpl.RequestService requestService, int requestId) { _requestService = requestService; _requestId = requestId; PeriodList = new ObservableCollection <PeriodDto>(_requestService.GetPeriods()); var request = _requestService.GetRequest(_requestId); if (request.ExecuteDate.HasValue && request.ExecuteDate.Value.Date > DateTime.MinValue) { SelectedDateTime = request.ExecuteDate.Value.Date; SelectedPeriod = PeriodList.SingleOrDefault(i => i.Id == request.PeriodId); OldDateTime = SelectedDateTime; OldPeriod = SelectedPeriod; } Refresh(null); }