public DateTime?SelectedDateTime()
    {
        var d = datePicker.SelectedDate;
        var t = timePicker.SelectedTime();

        if (d != null)
        {
            return(new DateTime(d.Value.Year, d.Value.Month, d.Value.Day,
                                t.Hour, t.Minute, t.Second));
        }
        return(null);
    }