How to stop UpdatePanel from causing whole page postback?

Question

I am using .NET 3.5 and building pages inside of the Community Server 2008 framework.

On one of the pages, I am trying to get an UpdatePanel working.

I took a sample straight from ASP.NET website, update a time in an UpdatePanel to current time by clicking a button, but for some reason when I try and perform the function the whole page refreshes.

Here is what I have:

protected void Button1_Click(object sender, EventArgs e)
{
    Label1.Text = "Panel refreshed at " + DateTime.Now.ToString();
    Label2.Text = "Panel refreshed at " + DateTime.Now.ToString();
}

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

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <ContentTemplate>
        <fieldset>
            <legend>UpdatePanel</legend>
            <asp:Label ID="Label1" runat="server" Text="Panel created."></asp:Label><br />
            <asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" />
        </fieldset>
    </ContentTemplate>
</asp:UpdatePanel>

Whenever I click the button, sure the panel updates - but the whole page posts back! I can see the whole page flashing. What the heck am I doing wrong?

I am inside of a nested Masterpage, but I'm not sure if this is a problem. Could there be something in this Community Server framework that I'm using that causes all events to postback?

Answer 1

Did you try setting Button1 as an AsyncPostBackTrigger in the Triggers section? Set the ChildrenAsTriggers property to true and the UpdateMode property to Conditional.

protected void Button1_Click(object sender, EventArgs e)
{    
    Label1.Text = "Panel refreshed at " + DateTime.Now.ToString();    
    UpdatePanel1.Update();
}    

<asp:ScriptManager ID="ScriptManager1" runat="server"/>
<asp:UpdatePanel ID="UpdatePanel1" runat="server" ChildrenAsTriggers="true" UpdateMode="Conditional">
    <Triggers>        
        <asp:AsyncPostBackTrigger ControlID="Button1" EventName="Click" />    
    </Triggers>    
    <ContentTemplate>        
        <fieldset>            
            <legend>UpdatePanel</legend>            
            <asp:Label ID="Label1" runat="server" Text="Panel created."></asp:Label><br />            
            <asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" />        
        </fieldset>    
    </ContentTemplate>
</asp:UpdatePanel>

Answer 2

I'm not seeing Label2 in your code sample above. If Label2 is located outside the UpdatePanel, a full page refresh will occur because that is what is required for the page to properly update Label2.

By default, UpdatePanels will only dynamically refresh the content within them, when triggered by controls within them. If you need to do some fancier updates, say a button outside of the panel causing the refresh or a label in a different panel to be updated, then you need to set the Conditional attribute on your UpdatePanel(s) and make some manual Update calls in your code.

Answer 3

Set ChildrenAsTriggers="true" on your UpdatePanel control.

Answer 4

"By default, UpdatePanels will only dynamically refresh the content within them, when triggered by controls within them."

Otherwise the whole page will be refreshed! Thats the point!

Answer 5

Another possible reason is that if the page has ClientIDMode="static", then controls that you expect to refresh just the UpdatePanel will refresh the whole page.

To fix the problem, you just need to set ClientIDMode="AutoID" on the control(s) which should trigger the UpdatePanel post back.

Answer 6

If you have an old project that was upgraded from .net framework v1.1, then remove this line from your web config to make it work:

<xhtmlConformance mode="Legacy"/>

That flag is added by the upgrade process and prevents partial page postbacks.