I want to add column and group to wingrid on runtime using the following codes.

But there is a bug. When the first time ChangeGroup function was invoked, the groups won't displayed, and if I use some method trying to get the group object, it throws an error. And when the ChangeGroup function was invoked by the second time and right after, the bug won't be exist any more, I don't what cause this bug.

If somebody tell me? Thank you!

AddGroups ag = new AddGroups();
ag.ChangeGroup(ultraGridShareholderRight,ht);

public class AddGroups
    {
        public void ChangeGroup( UltraGrid ultraGridZYYWSR, Hashtable ht)
        {
            String dataType = ht["datatype"].ToString();
            String startYear = ht["startyear"].ToString();
            String endYear = ht["endyear"].ToString();
            String startNum = ht["startnum"].ToString();
            String endNum = ht["endnum"].ToString();
           
            ultraGridZYYWSR.DisplayLayout.Bands[0].Groups.Add(columnName1, "");
            ultraGridZYYWSR.DisplayLayout.Bands[0].Columns.Add(columnName1, columnName1);
            ultraGridZYYWSR.DisplayLayout.Bands[0].Columns.Add("F_GSID", "F_GSID");
            ultraGridZYYWSR.DisplayLayout.Bands[0].Columns["F_GSID"].Hidden = true;
            ultraGridZYYWSR.DisplayLayout.Bands[0].Columns[columnName1].Width = 80;
            ultraGridZYYWSR.DisplayLayout.Bands[0].Columns[columnName1].Group = ultraGridZYYWSR.DisplayLayout.Bands[0].Groups[columnName1];
            if (dataType == "y")
            {
                int num = 0;
                int i = 0;
                for (i = Int32.Parse(endYear); i >= Int32.Parse(startYear) - 1; i--, num++)
                {
                    ultraGridZYYWSR.DisplayLayout.Bands[0].Groups.Add(i.ToString(), i.ToString() + "Year");
                    ultraGridZYYWSR.DisplayLayout.Bands[0].Groups[i.ToString()].Header.Appearance.TextHAlign = Infragistics.Win.HAlign.Center;
                    String columnNum = "Num" + num;
                    ultraGridZYYWSR.DisplayLayout.Bands[0].Columns.Add(columnNum, "Num");

                    ultraGridZYYWSR.DisplayLayout.Bands[0].Columns[columnNum].Group = ultraGridZYYWSR.DisplayLayout.Bands[0].Groups[i.ToString()];
                    ultraGridZYYWSR.DisplayLayout.Bands[0].Columns[columnNum].Width = 100;
                }
                ultraGridZYYWSR.DisplayLayout.Bands[0].Groups[(i + 1).ToString()].Hidden = true;
            }
    }