ScriptManager、UpdatePanel

<asp:ScriptManager ID="ScriptManager1" runat="server">

    </asp:ScriptManager>

    <asp:UpdatePanel ID="UpdatePanel1" runat="server">

       <ContentTemplate>

        <asp:DropDownList ID="DropDownList1" runat="server" 

            onselectedindexchanged="DropDownList1_SelectedIndexChanged">

            <asp:ListItem>1</asp:ListItem>

        </asp:DropDownList>

       </ContentTemplate>

            <Triggers>

                <asp:AsyncPostBackTrigger ControlID="DropDownList1" EventName="DropDownList1_SelectedIndexChanged" /> 

            </Triggers>

   </asp:UpdatePanel>

局部刷新，不知道哪里出错

对于 UpdatePanel“UpdatePanel1”中的触发器，未能在关联的控件“DropDownList1”上找到名为“DropDownList1_SelectedIndexChanged”的事件。
------解决方案--------------------
后台没定义DropDownList1_SelectedIndexChanged事件

看.cs文件里有这个吗？
public void DropDownList1_SelectedIndexChanged(object sender, EventsArg e)
{
   ...
}
------解决方案--------------------
DropDownList1_SelectedIndexChanged
后台没有这个方法吧