I’ve noticed a lot of discussion lately regarding methods to refresh an UpdatePanel via client script. This is very easy on the server side, of course. You can just call UpdatePanel.Update(). However, on the client side, the most common solutions I’ve been seeing just don’t feel right.

Many will advise you to use a hidden button control inside the UpdatePanel, manipulated via button.click(), to trigger a partial postback of the UpdatePanel. While it does work, I never have been able to get past the kludgey nature of that solution.


Finding a better way

To find a better solution, we’ll need a demonstration UpdatePanel to experiment with:

<asp:ScriptManager ID="ScriptManager1" runat="server" />
<div id="Container">
<asp:UpdatePanel runat="server" ID="UpdatePanel1"
   OnLoad="UpdatePanel1_Load">
 <ContentTemplate>
   <asp:Label runat="server" ID="Label1" />
 ContentTemplate>
asp:UpdatePanel>
protected void UpdatePanel1_Load(object sender, EventArgs e)
{
 Label1.Text = DateTime.Now.ToString();
}

That’s a slightly modified version of the standard UpdatePanel DateTime example. Instead of the more commonly used Button_Click trigger, notice that the UpdatePanel’s OnLoad event is handled in code-behind.

Anytime UpdatePanel1 is loaded or reloaded in a postback, Label1 will be updated to reflect the current date and time.

Never fear, __doPostBack() is here

Luckily, there’s an easy method for triggering a postback targeted at the UpdatePanel: __doPostBack().

As long as the event target of a __doPostBack() call is an async trigger of an UpdatePanel, the ASP.NET AJAX framework will intercept the postback and fire a partial postback instead. For purposes of demonstration, I’m going to add that to the OnClick event of the container div:

<div id="Container" onclick="__doPostBack('UpdatePanel1', '');">

Now, clicking anywhere in the UpdatePanel will trigger a partial postback, targeting the UpdatePanel. Since partial postbacks follow the full page lifecycle, this will fire UpdatePanel1_Load and update the Label’s text.

A word on _doPostBack

You may have noticed that there is also an ASP.NET AJAX specific method of the PageRequestManager named _doPostBack. While it works much like __doPostBack, as long as the ASP.NET AJAX client framework is present, you should not call it directly.

The original __doPostBack method performs identically, but is more robust since it gracefully degrades to full postbacks when the ASP.NET AJAX framework isn’t available. It’s also unlikely that __doPostBack will disappear in future versions of ASP.NET, while it’s less assured that the ASP.NET AJAX framework will remain unchanged.