public DateTime? LogDate
        {
            get { return _logDate; }
            set
            {
                if (value == _logDate)
                {
                    return;
                }

                _logDate = value;

                base.OnPropertyChanged("LogDate");

                string date = _logDate == null ? "null" : _logDate.ToString();

                Debug.WriteLine("logDate = " + date);

            }
        }

        private void RadioButton_Checked(object sender, RoutedEventArgs e)
        {
            buttonRefresh.Focus();
            ((RadioButton)sender).Focus();
        }