大家帮我看一看，问什么我点了button后，datalist没有变化啊？

页面代码：
<asp:DataList ID="DataList1" runat="server" BackColor="White" BorderColor="#E7E7FF"
            BorderStyle="None" BorderWidth="1px" CellPadding="3" GridLines="Horizontal" Height="171px" Width="138px">
            <FooterStyle BackColor="#B5C7DE" ForeColor="#4A3C8C" />
            <SelectedItemStyle BackColor="#738A9C" Font-Bold="True" ForeColor="#F7F7F7" />
            <ItemTemplate>
                <asp:Button ID="Button1" runat="server" Text="选择" CommandName="select" />
                <%#DataBinder.Eval(Container.DataItem,"Sex") %>
            </ItemTemplate>
            <AlternatingItemStyle BackColor="#F7F7F7" />
            <ItemStyle BackColor="#E7E7FF" ForeColor="#4A3C8C" />
            <HeaderStyle BackColor="#4A3C8C" Font-Bold="True" ForeColor="#F7F7F7" />
            <SelectedItemTemplate>
                Name:<%#DataBinder.Eval(Container.DataItem, "departmentname")%>
            </SelectedItemTemplate>
        </asp:DataList>&nbsp;后台代码：if (e.CommandName == "select")
        {
            DataList1.SelectedIndex = e.Item.ItemIndex;
            DataList1.DataBind();
        
        }