BeemerGuy BeemerGuy - 3 months ago 22
Javascript Question

Partial postback with Javascript

I couldn't find something similar in SO.

In ASP.NET, is there any way that on cue I can cause a partial postback with Javascript in an UpdatePanel?

I tried

__doPostBack()
but it does a full postback.

I can trick it with a dummy button and fire
click()
then handle the partial postback that way, but I want a more graceful way than trickery.

Thanks.

Edit: I found this disturbedbuddha.wordpress.com/2007/11/26/… but I can't get it to work =(

I would love for this method to work; it's perfect for me!
So far what I can do using this last method is gain reference to the timer. With the timer initially disabled, starting the timer doesn't seem to cause a postback. However, without Ajax, if I simply have the timer enabled initially, it posts back at intervals just fine; why can't the Ajax call cause it?

Answer

You can use an AsyncPostBackTrigger with the UpdatePanel to do this. Because you need something that can fire an event, using a button is fairly simple and when hidden works nicely.

If this is your markup:

<asp:UpdatePanel ID="UpdatePanel1" runat="server" OnLoad="UpdatePanel1_Load">
    <ContentTemplate>
        <!-- Contents... -->
    </ContentTemplate>
    <Triggers>
        <asp:AsyncPostBackTrigger ControlID="ReloadThePanel" EventName="Click" />
    </Triggers>
</asp:UpdatePanel>
<asp:Button ID="ReloadThePanel" runat="server" style="display:none;" />

When you want the panel to be updated, you just need to call:

__doPostBack('<%=ReloadThePanel.ClientID %>', null);

This will make ASP.NET think that ReloadThePanel was clicked and the JavaScript auto-generated due to the trigger will handle the rest.

EDIT

You can do a pure JavaScript update of the UpdatePanel without any triggers or hidden buttons. You just need to invoke __doPostBack with the client-side ID as the first argument.

__doPostBack('<%=UpdatePanel1.ClientID %>', null);
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