<asp:DropDownList ID="ddlRegionList" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddlDeptList_SelectedIndexChanged">
                        <asp:ListItem>是</asp:ListItem>
                        <asp:ListItem>否</asp:ListItem>
                    </asp:DropDownList>

 protected void ddlDeptList_SelectedIndexChanged(object sender, EventArgs e)
        {

  code.....
            FillDG();
            FillUI();
        }