private void button1_Click(object sender, EventArgs e)
    {
      DataTable dt = new DataTable();
      dt.Columns.Add("Group");
      dt.Columns.Add("idex");
      dt.Columns.Add("name");
      for (int i = 0; i < 5; i++)
      {
        DataRow dr = dt.NewRow();
        dr["Group"] = "<5";
        dr["idex"] = i.ToString();
        dr["name"] = "姓名" + i.ToString();
        dt.Rows.Add(dr);
      }
      for (int i = 5; i <= 10; i++)
      {
        DataRow dr = dt.NewRow();
        dr["Group"] = "(5,10]";
        dr["idex"] = i.ToString();
        dr["name"] = "姓名" + i.ToString();
        dt.Rows.Add(dr);
      }
      for (int i = 10; i <= 15; i++)
      {
        DataRow dr = dt.NewRow();
        dr["Group"] = "(10,15]";
        dr["idex"] = i.ToString();
        dr["name"] = "姓名" + i.ToString();
        dt.Rows.Add(dr);
      }
      gridColumnNumber.FieldName = "idex";
      gridColumnName.FieldName = "name";
      gridColumnGroup.FieldName = "Group";
      gridColumnGroup.GroupIndex = 0;
      gdc.DataSource = dt;
      gdv.ExpandAllGroups();
      for (int i = -1; gdv.IsGroupRow(i); i--)
      {
        DataRow dr = gdv.GetDataRow(gdv.GetDataRowHandleByGroupRowHandle(i));
        if (dr == null) return;
        if (dr["Group"].ToString() == "(5,10]")
        {
          gdv.CollapseAllGroups();
          gdv.FocusedRowHandle = i;
          gdv.SetRowExpanded(i, true);
          return;
        }
      }
    }