在gridview编辑模板中的DropDownList的事件发生在"更新"操作的前面呀??急,在线等.

我是这样的:
 <asp:GridView ID="GridView1" runat="server" AllowSorting="True" AutoGenerateColumns="False" OnSelectedIndexChanged="ToEditBind"
            DataKeyNames="NumID" DataSourceID="SqlDataSource1" BackColor="LightGoldenrodYellow" BorderColor="Tan" BorderWidth="1px" CellPadding="2" GridLines="None" ForeColor="Black">
            <Columns>
                <asp:BoundField DataField="NumID" HeaderText="NumID" InsertVisible="False" ReadOnly="True"
                    SortExpression="NumID" />
                <asp:BoundField DataField="IID" HeaderText="IID" SortExpression="IID" />
                <asp:BoundField DataField="ColumnName" HeaderText="ColumnName" SortExpression="ColumnName" />
                <asp:BoundField DataField="ChannelID"  ReadOnly="True" HeaderText="ChannelID" SortExpression="ChannelID" />
                <asp:TemplateField HeaderText="ChannelName" SortExpression="ChannelName">
                  <EditItemTemplate>
                     <asp:DropDownList ID="Drplist" runat="server" DataSourceID="SqlDataSource2"  DataTextField="ChannelName" DataValueField="ChannelName"  OnSelectedIndexChanged="ChangeChannelID" OnTextChanged="ChangeChannelID" SelectedValue='<%# Bind("ChannelName") %>'>
                        </asp:DropDownList>                  </EditItemTemplate>
                  <ItemTemplate>
                     <asp:Label ID="Cid" runat="server" Text='<%# Bind("ChannelName") %>'></asp:Label>
                 </ItemTemplate>
               </asp:TemplateField>
                <asp:CommandField ShowDeleteButton="True" ShowEditButton="True" />
            </Columns>我在<asp:DropDownList ID="Drplist" runat="server" DataSourceID="SqlDataSource2"  DataTextField="ChannelName" DataValueField="ChannelName"  OnSelectedIndexChanged="ChangeChannelID" OnTextChanged="ChangeChannelID" SelectedValue='<%# Bind("ChannelName") %>'>
                        </asp:DropDownList>这里的DropDownList里加上一个OnSelectedIndexChanged事件
但他触发的时候是在点了"更新"操作后才触发,我想它在没有点击"更新"前,也就是当选项值改变时就触发应该怎么做呀,急呀,请名位高手指点指点.