Asp.net Repeater 排序

<table>
<asp:Repeater ID="Repeater1" runat="server" OnItemCommand="Repeater1_ItemCommand"
                    OnItemDataBound="Repeater1_ItemDataBound">
        <HeaderTemplate>
             <tr>
                  <th>
                       <asp:LinkButton ID="specialtyName" runat="server" CommandName="specialtyName">专业</asp:LinkButton>
                  </th>
                  <th>
                       <asp:LinkButton ID="classId" runat="server" CommandName="classId">班号</asp:LinkButton>
                  </th>
                  <th>
                       <asp:LinkButton ID="className" runat="server" CommandName="className">班级名称</asp:LinkButton>
                  </th>
                  <th>
                       <asp:LinkButton ID="grade" runat="server" CommandName="grade">年级</asp:LinkButton>
                  </th>
                  <th>
                       <asp:LinkButton ID="classNo" runat="server" CommandName="classNo">班级人数</asp:LinkButton>
                  </th>
                  <th>
                       <asp:LinkButton ID="length" runat="server" CommandName="length">学制</asp:LinkButton>
                  </th>
                  <th>
                       <asp:LinkButton ID="assistantId" runat="server" CommandName="assistantId">辅导员号</asp:LinkButton>
                  </th>
                  <th>
                       <asp:LinkButton ID="explain" runat="server" CommandName="explain">备注</asp:LinkButton>
                  </th>
                  <th>
                       <asp:LinkButton ID="action" runat="server" CommandName="action">操作</asp:LinkButton>
                  </th>
             </tr>
        </HeaderTemplate>
        <ItemTemplate>
             <tr>
                  <td>
                       <%# eval("specialtyName")%>
                  </td>
                  <td>
                       <%# eval("classId")%>
                  </td>
                  <td>
                       <%# eval("className") %>
                  </td>
                  <td>
                       <%# eval("grade") %>
                  </td>
                  <td>
                       <%# eval("classNo")%>
                  </td>
                  <td>
                       <%# eval("length") %>
                  </td>
                  <td>
                       <%# eval_r("assistantId")%>
                  </td>
                  <td>
                       <%# eval("explain")%>
                  </td>
                  <td>
                       <a href="#">删除</a>
                  </td>
             </tr>
        </ItemTemplate>
</asp:Repeater>
</table>
  后台代码:
    protected void Page_Load(object sender, EventArgs e)
    {
         //这里是将数据库的数据绑定到repeater控件上，由于代码因工程而异，所以就不写了
         //绑定返回类型为DataTable dt
         GetData=dt.DefaultView;
    }
     protected void Repeater1_ItemDataBound(object sender, RepeaterItemEventArgs e)
        {
            if (e.Item.ItemType == ListItemType.Header)
            {
                if (ViewState["id"] != null)
                {
                    LinkButton lkbtnSort = (LinkButton)e.Item.FindControl(ViewState["id"].ToString().Trim());
                    lkbtnSort.Text = ViewState["text"].ToString();
                }
            }
        }
     protected void Repeater1_ItemCommand(object source, RepeaterCommandEventArgs e)
        {
            if (e.Item.ItemType == ListItemType.Header)
            {
                LinkButton lkbtnSort = (LinkButton)e.Item.FindControl(e.CommandName.Trim());
                if (ViewState[e.CommandName.Trim()] == null)
                {
                    ViewState[e.CommandName.Trim()] = "ASC";
                    lkbtnSort.Text = lkbtnSort.Text + "▲";
                }
                else
                {
                    if (ViewState[e.CommandName.Trim()].ToString().Trim() == "ASC")
                    {
                        ViewState[e.CommandName.Trim()] = "DESC";
                        if (lkbtnSort.Text.IndexOf("▲") != -1)
                            lkbtnSort.Text = lkbtnSort.Text.Replace("▲", "▼");
                        else
                            lkbtnSort.Text = lkbtnSort.Text + "▼";
                    }
                    else
                    {
                        ViewState[e.CommandName.Trim()] = "ASC";
                        if (lkbtnSort.Text.IndexOf("▼") != -1)
                            lkbtnSort.Text = lkbtnSort.Text.Trim().Replace("▼", "▲");
                        else
                            lkbtnSort.Text = lkbtnSort.Text + "▲";
                    }
                }
                ViewState["text"] = lkbtnSort.Text;
                ViewState["id"] = e.CommandName.Trim();
                DataView dv = GetData;
                dv.Sort = e.CommandName.ToString().Trim() + " " + ViewState[e.CommandName.Trim()].ToString().Trim();
                Repeater1.DataSource = dv;
                Repeater1.DataBind();
            }
        }
     private DataView GetData
        {
            get
            {
                return Cache["_data"] as DataView;
            }
            set
            {
                Cache["_data"] = value;
            }
        }