DropDownList 的联动效果

asp:DropDownList 的联动效果：
<asp:DropDownList ID="drpLstYear" runat="server" Height="16px"
          Width="104px" onselectedindexchanged="drpLstYear_SelectedIndexChanged" AutoPostBack="True">
      <asp:ListItem Selected="True">2005</asp:ListItem>
      <asp:ListItem>2006</asp:ListItem>
      <asp:ListItem>2007</asp:ListItem>
      <asp:ListItem>2008</asp:ListItem>
      <asp:ListItem>2009</asp:ListItem>
      <asp:ListItem>2010</asp:ListItem>
    </asp:DropDownList>

被设置的成员：<asp:DropDownList ID="drpLstMemName" runat="server" Height="16px"
          Width="83px" onselectedindexchanged="drpLstMemName_SelectedIndexChanged">
      </asp:DropDownList>
                            <asp:ObjectDataSource ID="ObjectDataSource1" runat="server"

SelectMethod="GetMemNameForGrade" TypeName="OfficeAnywhere.MemInfo.BLL.MemManage">
                                <SelectParameters>
                                    <asp:ControlParameter ControlID="drpLstYear" DefaultValue="drpLstYear.Text"
                                        Name="grade" PropertyName="SelectedValue" Type="Int32" />
                                </SelectParameters>
      </asp:ObjectDataSource>

protected void drpLstYear_SelectedIndexChanged(object sender, EventArgs e)
        {
            MemManage memManage = new MemManage();
            DataTable dataTable = memManage.GetMemNameForGrade(int.Parse(drpLstYear.Text));
            drpLstMemName.DataSource = dataTable;
            drpLstMemName.DataTextField = "MemName";
            drpLstMemName.DataValueField = "MemId";
            drpLstMemName.DataBind();
            drpLstMemName.Items.Add("");
        }