public BaseOrderViewModel()
        {
            IsCurrentSelected = new NotifyValue <bool>(true);
            IsSentSelected    = new NotifyValue <bool>();
            IsDeletedSelected = new NotifyValue <bool>();
            Begin             = new NotifyValue <DateTime>(DateTime.Today.AddMonths(-3).FirstDayOfMonth());
            End          = new NotifyValue <DateTime>(DateTime.Today);
            BeginEnabled = IsSentSelected.ToValue();
            EndEnabled   = IsSentSelected.ToValue();

            IsCurrentSelected.Subscribe(_ => NotifyOfPropertyChange("CanPrint"));
            IsCurrentSelected.Subscribe(_ => NotifyOfPropertyChange(nameof(CanExport)));
            SessionValue(Begin, "Begin");
            SessionValue(End, "End");
        }