寻呼机模板的下拉列表无法正常工作

Question

我在我的项目中实现了pagerTemplate功能，并参考了Here。但问题是下拉列表不能正常工作。当我更改选择时，gridview不会返回确切的结果。请按照我在此处实施的方式查看代码。

<asp:GridView ID="grdTeacherProfile" runat="server" Width="100%" border="1" Style="border: 1px solid #E5E5E5;" CellPadding="3" FooterStyle-BackColor="#e3e3e3"
                AutoGenerateColumns="false" AllowPaging="true" CssClass="hoverTable" DataKeyNames="Id" PageSize="3" ShowFooter="true" HeaderStyle-CssClass="k-grid td"
                OnDataBound="grdTeacherProfile_DataBound" OnPageIndexChanging="grdTeacherProfile_PageIndexChanging" OnRowDeleting="grdTeacherProfile_RowDeleting"
                OnRowUpdating="grdTeacherProfile_RowUpdating" OnRowEditing="grdTeacherProfile_RowEditing" OnRowCancelingEdit="grdTeacherProfile_RowCancelingEdit"
                EmptyDataText="No records found">
                <AlternatingRowStyle BackColor="#E9E9E9" />
                <Columns>
                    <asp:BoundField DataField="first_name" HeaderText="First Name" ItemStyle-Width="25" ControlStyle-CssClass="k-grid td" />
                    <asp:BoundField DataField="last_name" HeaderText="Last Name" ItemStyle-Width="30" ControlStyle-CssClass="k-grid td" />
                    <asp:BoundField DataField="dob" HeaderText="Date of Birth" ItemStyle-Width="20" ControlStyle-CssClass="k-grid td" ApplyFormatInEditMode="true" DataFormatString="{0:d}" />
                    <asp:BoundField DataField="gender" HeaderText="Gender" ItemStyle-Width="20" ControlStyle-CssClass="k-grid td" />
                    <asp:BoundField DataField="designation" HeaderText="Designation" ItemStyle-Width="20" ControlStyle-CssClass="k-grid td" />
                    <asp:BoundField DataField="joining_date" HeaderText="Joining Date" ItemStyle-Width="20" ControlStyle-CssClass="k-grid td" ApplyFormatInEditMode="true" DataFormatString="{0:d}" />
                    <asp:BoundField DataField="leaving_date" HeaderText="Leaving Date" ItemStyle-Width="20" ControlStyle-CssClass="k-grid td" ApplyFormatInEditMode="true" DataFormatString="{0:d}" />
                    <asp:BoundField DataField="active" HeaderText="Active" ItemStyle-Width="25" ControlStyle-CssClass="k-grid td" />
                    <asp:TemplateField HeaderText="Action" HeaderStyle-Width="5%">
                        <ItemTemplate>
                            <asp:ImageButton ID="btnDelete" AlternateText="Delete" ImageUrl="~/images/delete.png" runat="server" Width="15" Height="15" CommandName="Delete" CommandArgument='<%# Eval("Id") %>' CausesValidation="false" OnClientClick="return confirm('Are you sure you want to delete this record?')" />
                            <asp:ImageButton ID="btnEdit" ImageUrl="~/images/edit.png" ControlStyle-Width="15" CausesValidation="false" ControlStyle-Height="15" runat="server"></asp:ImageButton>
                        </ItemTemplate>
                    </asp:TemplateField>
                </Columns>
                <FooterStyle BackColor="#D8DADA" Font-Bold="True" />
                <RowStyle BackColor="white" BorderStyle="Solid" BorderColor="#a8a8a8" BorderWidth="1px" Height="35" />
                <PagerTemplate>
                    <table style="width:100%">
                        <tr>
                            <td style="width:auto; float:right;">
                                <asp:Label ID="MessageLabel" runat="server" Text="Select the page"></asp:Label>&nbsp;
                                <asp:DropDownList ID="ddlPageSort" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddlPageSort_SelectedIndexChanged" ></asp:DropDownList>
                            </td>

                            <td style="width:auto; float:left;">
                                <asp:Label ID="CurrentPageLabel" runat="server" Text=""></asp:Label>
                            </td>
                        </tr>
                    </table>
                </PagerTemplate>
            </asp:GridView>

另见背后的代码： -

protected void grdTeacherProfile_DataBound(object sender, EventArgs e)
    {
        GridViewRow pagerRow = grdTeacherProfile.BottomPagerRow;

        // Retrieve the DropDownList and Label controls from the row.
        DropDownList pageList = (DropDownList)pagerRow.Cells[0].FindControl("ddlPageSort");
        Label pageLabel = (Label)pagerRow.Cells[0].FindControl("CurrentPageLabel");

        if (pageList != null)
        {
            for (int i = 0; i < grdTeacherProfile.PageCount; i++)
            {
                // Create a ListItem object to represent a page.
                int pageNumber = i + 1;
                ListItem item = new ListItem(pageNumber.ToString());

                if (i == grdTeacherProfile.PageIndex)
                {
                    item.Selected = true;
                }
                // Add the ListItem object to the Items collection of the 
                // DropDownList.
                pageList.Items.Add(item);
            }
        }
        if (pageLabel != null)
        {
            // Calculate the current page number.
            int currentPage = grdTeacherProfile.PageIndex + 1;
            // Update the Label control with the current page information.
            pageLabel.Text = "Page " + currentPage.ToString() + " of " + grdTeacherProfile.PageCount.ToString();
        }

}

protected void ddlPageSort_SelectedIndexChanged(object sender, EventArgs e)
    {
        GridViewRow pagerRow = grdTeacherProfile.BottomPagerRow;
        DropDownList pageList = (DropDownList)pagerRow.Cells[0].FindControl("ddlPageSort");
        grdTeacherProfile.PageIndex = pageList.SelectedIndex;
    }