Jan 16

Today I”ve seen an interesting thread in the AJAX foruns. The problem was how to make a traditional HTML control refresh an UpdatePanel. The answer turned out to be simple. Before showing some code (which could also be written in a slightly different way!), it”s important to understand when a partial postbacks happens.

The PageRequestManager intercepts all the postbacks that happen on a page that has UpdatePanels. A partial postback happens when the control that starts this action is placed inside an UpdatePanel or maintained in the async control list (an internal field of the class). The following code uses this info to add a textbox to that list and handles the change event by starting a postback. This is all that is necessary to have a partial postback!

Another thing need was the ability to refresh an UpdatePanel when the partial postback was started by that control. In the code, I perform a simple check and try to see if the responsible for the postback is my HTML textbox. If it is, then I need to update the panel by calling its update method (ie, you”re seeing something similar to what happens when you triggers – ie, triggers use code similar to this one).


<%@ Page Language=”C#” AutoEventWireup=”true” %>
<script runat=”server”>
protected override void OnLoad(EventArgs e)

if (ScriptManager1.IsInAsyncPostBack &&
Request.Params[“__EVENTTARGET”] == “txt”)
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “”>
<html xmlns=”” >
<head id=”Head1″ runat=”server”>
<title>Untitled Page</title>
<form id=”form1″ runat=”server”>
<asp:ScriptManager ID=”ScriptManager1″ runat=”server” />

<asp:updatepanel runat=”server” id=”panel” UpdateMode=”Conditional”>
       panel 1: <%= DateTime.Now.ToString() %>
<asp:updatepanel runat=”server” id=”Updatepanel1″ UpdateMode=”Conditional”>
       panel 2:<%= DateTime.Now.ToString() %>
<input type=”text” id=”txt” onchange=”__doPostBack(”txt”,””);” />
<script type=”text/javascript”>
    Sys.WebForms.PageRequestManager.getInstance().add_pageLoaded( function() {
         Sys.WebForms.PageRequestManager.getInstance()._asyncPostBackControlClientIDs.push( “txt” );} );

2 comments so far

  1. Bart
    6:09 pm - 11-12-2007

    I don”t know if you”ll check this, But I have an interesting one for you:

    I have nested datalists (master-detail) set up to appear like an explorer window and when you click the master it shows the div that was hiding the detail items. I am trying to get the detail to do a partial page update when it gets shown.

    my update panels are named dynamically and so are the triggers. how do I assign the triggers to specific panels through javascript or in the code behind?



  2. Luis Abreu
    7:25 pm - 11-12-2007

    yes, i do read the comments, but sometimes i do take some time to answer.

    regarding your question, if you”re adding trigers from the code behind, then maks sure you add them until the init event (if i recall it correctly, doing it after won”t work correctly).

    from jscript, it”s really simple, you just need to submit the form by using the good old __doPostback methof and passing the client id of the update panel:

    hope this helps.