DevGridControl中GridView排序問題

因數據源中需要顯示**等內容 所以數據列是string類型，字元串類型排序時，結果如下：

gridColumn1.SortMode = DevExpress.XtraGrid.ColumnSortMode.Custom;

然後在事件CustomColumnSort中實現

        void gdv_CustomColumnSort(object sender, DevExpress.XtraGrid.Views.Base.CustomColumnSortEventArgs e)
        {
            if (e.Column != null && e.Value1 != null && e.Value2 != null)
            {
                string value1 = e.Value1.ToString();
                string value2 = e.Value2.ToString();
                int result = Comparer.Default.Compare
                    (ConvertToDecimal(value1, e.SortOrder), ConvertToDecimal(value2, e.SortOrder));
                e.Result = result;
                e.Handled = true;
            }
        }

        private decimal ConvertToDecimal(string input, DevExpress.Data.ColumnSortOrder sortOrder)
        {
            decimal result = 0;
            if (string.IsNullOrWhiteSpace(input) || input.Equals("**") || input.Equals("--"))
                result = sortOrder == DevExpress.Data.ColumnSortOrder.Ascending ? 9999 : -9999;
            else
                decimal.TryParse(input, out result);
            return result;
        }

gridColumn1.SortMode = DevExpress.XtraGrid.ColumnSortMode.Value;