Determine which UpdatePanel causes the partial (asynchronous) PostBack?

Question

In a page contains two UpdatePanels, How can I know which UpdatePanel causes the partial PostBack ?

I mean in the Page_Load event handler.

This is my code:

 <asp:ScriptManager ID="ScriptManager1" runat="server">
 </asp:ScriptManager>
 <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional" 
     onprerender="UpdatePanel1_PreRender">
     <ContentTemplate>
         <A:u1 ID="u1" runat="server" />
     </ContentTemplate>
 </asp:UpdatePanel>
 <asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional" 
     onprerender="UpdatePanel2_PreRender">
     <ContentTemplate>
         <A:u2 ID="u2" runat="server" />
     </ContentTemplate>
 </asp:UpdatePanel>

I tried this code, but it isn't worked alost!

protected void Page_Load(object sender, EventArgs e)
{
    if (ScriptManager.GetCurrent(Page).IsInAsyncPostBack)
    {
        if (UpdatePanel1.IsInPartialRendering)
        {
            // never enter to here
        }
        if (UpdatePanel2.IsInPartialRendering)
        {
            // neither here
        }
    }
}

Any help!

Answer 1

You can use the IsInPartialRendering property of the UpdatePanel class to determine if a specific panel caused the partial postback:

protected void Page_Render(object sender, EventArgs e)
{
    if (ScriptManager.GetCurrent(Page).IsInAsyncPostBack) {
        if (yourFirstUpdatePanel.IsInPartialRendering) {
            // The first UpdatePanel caused the partial postback.
        } else if (yourSecondUpdatePanel.IsInPartialRendering) {
            // The second UpdatePanel caused the partial postback.
        }
    }
}

EDIT: It appears that IsInPartialRendering is always false before the Render phase. Since you want that information during the Load phase, it won't work as expected. See this bug.

There's a workaround documented here that consists in deriving your own class from UpdatePanel to access its protected RequiresUpdate property:

public class ExtendedUpdatePanel : UpdatePanel
{
    public bool IsUpdating
    {
        get {
            return RequiresUpdate;
        }
    }
}

After replacing asp:UpdatePanel with ExtendedUpdatePanel in your page markup, the code above becomes:

protected void Page_Load(object sender, EventArgs e)
{
    if (ScriptManager.GetCurrent(Page).IsInAsyncPostBack) {
        if (yourFirstUpdatePanel.IsUpdating) {
            // The first UpdatePanel caused the partial postback.
        } else if (yourSecondUpdatePanel.IsUpdating) {
            // The second UpdatePanel caused the partial postback.
        }
    }
}