关于datagrid表头排序的问题~~~急~~在线等~~~

OnSortCommand方法eg:
<%@ Page Language="C#" AutoEventWireup="True" %>
<%@ Import Namespace="System.Data" %>
 
<html>
   <script runat="server">
 
      ICollection CreateDataSource()
      {
      
         // Create a Random object to mix up the order of items in the sample data.
         Random Rand_Num = new Random();         // Create sample data for the DataGrid control.
         DataTable dt = new DataTable();
         DataRow dr;
 
         // Define the columns of the table.
         dt.Columns.Add(new DataColumn("IntegerValue", typeof(Int32)));
         dt.Columns.Add(new DataColumn("StringValue", typeof(String)));
         dt.Columns.Add(new DataColumn("CurrencyValue", typeof(Double)));
 
         // Populate the table with sample values.
         for (int i=0; i<=8; i++) 
         {            dr = dt.NewRow();
 
            dr[0] = i;
            dr[1] = "Item " + Rand_Num.Next(1, 15).ToString();
            dr[2] = 1.23 * Rand_Num.Next(1, 15);
 
            dt.Rows.Add(dr);
         
         }         // To persist the data source between posts to the server, store it
         // in session state.  
         Session["Source"] = dt;
 
         DataView dv = new DataView(dt);         return dv;
      
      }
 
      void Page_Load(Object sender, EventArgs e)
      { 
 
         // Load sample data only once, when the page is first loaded.
         if (!IsPostBack)
         { 
         
            ItemsGrid.DataSource = CreateDataSource();
            ItemsGrid.DataBind();
         
         }         // Manually register the event-handling method for the PageIndexChanged  
         // event of the DataGrid control.
         ItemsGrid.SortCommand += new DataGridSortCommandEventHandler(this.Sort_Grid);      }      void Sort_Grid(Object sender, DataGridSortCommandEventArgs e)
      {          // Retrieve the data source from session state.
         DataTable dt = (DataTable)Session["Source"];         // Create a DataView from the DataTable.
         DataView dv = new DataView(dt);         // The DataView provides an easy way to sort. Simply set the Sort property with
         // the name of the field to sort by.
         dv.Sort = e.SortExpression;         // Re-bind the data source and specify that it should be sorted
         // by the field specified in the SortExpression property.
         ItemsGrid.DataSource = dv;
         ItemsGrid.DataBind();      }      void Check_Change(Object sender, EventArgs e)
      {
   
         // Allow or prevent sorting depending on the user's selection.
         if (AllowSortingCheckBox.Checked)
         {            ItemsGrid.AllowSorting = true;         }
         else
         {            ItemsGrid.AllowSorting = false;         }         // After changing the property, re-bind the data to
         // refresh the DataGrid control.         // Retrieve the data source from session state.
         DataTable dt = (DataTable)Session["Source"];         // Create a DataView from the DataTable.
         DataView dv = new DataView(dt);         // Re-bind the data source.
         ItemsGrid.DataSource = dv;
         ItemsGrid.DataBind();      }   </script>
 
<body>
 
   <form runat=server>
 
      <h3>DataGrid SortCommand Example</h3>      Select whether to allow sorting in the DataGrid control.      <br><br>
 
      <b>Product List</b>
 
      <asp:DataGrid id="ItemsGrid"
           BorderColor="black"
           BorderWidth="1"
           CellPadding="3"
           AutoGenerateColumns="False"
           AllowSorting="True"
           runat="server">         <HeaderStyle BackColor="#00aaaa">
         </HeaderStyle>         <Columns>            <asp:BoundColumn DataField="IntegerValue" 
                 SortExpression="IntegerValue"
                 HeaderText="Item"/>            <asp:BoundColumn DataField="StringValue"
                 SortExpression="StringValue" 
                 HeaderText="Description"/>            <asp:BoundColumn DataField="CurrencyValue" 
                 HeaderText="Price"
                 SortExpression="CurrencyValue"
                 DataFormatString="{0:c}">               <ItemStyle HorizontalAlign="Right">
               </ItemStyle>            </asp:BoundColumn>         </Columns> 
 
      </asp:DataGrid>      <hr>      <asp:CheckBox id="AllowSortingCheckBox"
           Text="Allow sorting"
           AutoPostBack="True"
           Checked="True"
           OnCheckedChanged="Check_Change"
           runat="server"/>
 
   </form>
 
</body>
</html>