DataGrid的问题

你自己看一下以下例子吧!
<%@ Import Namespace="System.Data" %><html>
<script language="C#" runat="server">    string SortField;    ICollection CreateDataSource() {
        DataTable dt = new DataTable();
        DataRow dr;        dt.Columns.Add(new DataColumn("IntegerValue", typeof(Int32)));
        dt.Columns.Add(new DataColumn("StringValue", typeof(string)));
        dt.Columns.Add(new DataColumn("DateTimeValue", typeof(DateTime)));
        dt.Columns.Add(new DataColumn("BoolValue", typeof(bool)));
        dt.Columns.Add(new DataColumn("CurrencyValue", typeof(double)));        for (int i = 0; i < 9; i++) {
            dr = dt.NewRow();            dr[0] = 9-i;
            dr[1] = "Item " + i.ToString();
            dr[2] = new DateTime(2000,1,1);
            dr[3] = (i % 2 != 0) ? true : false;
            dr[4] = 1.23 * (i+1);            dt.Rows.Add(dr);
        }        DataView dv = new DataView(dt);
        dv.Sort = SortField;
        return dv;
    }    void Page_Load(Object sender, EventArgs e) {
        if (!IsPostBack) {
            if (SortField == "") {
                SortField = "IntegerValue";
            }
            BindGrid();
        }
    }    protected void MyDataGrid_Sort(Object sender, DataGridSortCommandEventArgs e) {
        SortField = (string)e.SortExpression;
        BindGrid();
    }    public void BindGrid() {
        MyDataGrid.DataSource = CreateDataSource();
        MyDataGrid.DataBind();
    }
</script><body>    <h3><font face="Verdana">Custom Sorting in DataGrid</font></h3>    <form runat=server>      <ASP:DataGrid id="MyDataGrid" runat="server"
        BorderColor="black"
        BorderWidth="1"
        CellPadding="3"
        Font-Name="Verdana"
        Font-Size="8pt"
        HeaderStyle-BackColor="#cccccc"
        HeaderStyle-ForeColor="black"
        AutoGenerateColumns="false"
        AllowSorting="true"
        OnSortCommand="MyDataGrid_Sort"
      >
          <Columns>
            <asp:BoundColumn HeaderText="Sortable" DataField="IntegerValue" SortExpression="IntegerValue"/>
            <asp:BoundColumn HeaderText="Not Sortable" DataField="DateTimeValue" />
            <asp:TemplateColumn
                SortExpression="StringValue">
                <HeaderTemplate>
                    Click to sort -->
                    <asp:ImageButton id=SortButton1 runat="server"
                        CommandName="sort"
                        ImageUrl="/quickstart/aspplus/images/arrow1.gif"
                        />
                </HeaderTemplate>
                <ItemTemplate>
                    <asp:Label runat="server"
                        Text='<%# DataBinder.Eval(Container, "DataItem.StringValue") %>' />
                </ItemTemplate>
            </asp:TemplateColumn>
          </Columns>      </asp:DataGrid>  </form></body>
</html>