ASP.NET DropDownList OnSelectedIndexChanged event not fired

I'm trying to use some AJAX and ASP.Net together to enable me to run functions without having to refresh the wh开发者_运维知识库ole page but i've stumbled across a problem in doing this

Here's my code

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

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <ContentTemplate>
        <asp:DropDownList ID="ddl1" runat="server" OnSelectedIndexChanged="update1" />

        <asp:TextBox runat="server" ID="txt1" />

    </ContentTemplate>
</asp:UpdatePanel>

And here's my code behind

 Sub update1(ByVal sender As Object, ByVal e As EventArgs)

    txt1.Text = Now.ToString

End Sub

The event doesn't fire because I don't have AutoPostBack="True" on my ddl but adding that to the ddl will postback the whole page.

Is there a way to avoid using AutoPostBack="True" so that it only updates the panel?

I know I can use an asp:Button to get around this but i'd really like to be able to use a ddl with OnSelectedIndexChanged

Thanks

If you want to avoid to send the whole viewstate to the server, you should look at callbacks.

Instead, if you want to avoid a refresh of the entire page, but with postback, this should work:

<asp:DropDownList ID="ddl1" runat="server" OnSelectedIndexChanged="update1" AutoPostBack="True"  />

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <Triggers>
         <asp:AsyncPostbackTrigger ControlID="ddl1" EventName="SelectedIndexChanged" />
    </Triggers>
    <ContentTemplate>
        <asp:TextBox runat="server" ID="txt1" />
    </ContentTemplate>
</asp:UpdatePanel>

Try creating a new page with same codes and different page name. Worked for me