trigger controlID from user control page - asp.net

Question

I have the code below which looks like it should work. However, the trigger that references the control with the controlID of "gvSearch" is actually a gridview inside a user control page.
How can I access that gridview so that I can use it as a trigger?
Thanks!
<asp:UpdatePanel ID="pnlSearch" ChildrenAsTriggers="true" runat="server" >
<Triggers>
<asp:AsyncPostBackTrigger ControlID="btnSearch" />
<asp:AsyncPostBackTrigger ControlID="gvSearch" />
</Triggers>
</asp:UpdatePanel>
Thanks!
Outline:
<%# Page Title="test">
<%# Register src="test1.ascx" tagname="test1" tagprefix="test1uc" %>
<UpdatePanel>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="btnSearch" />
<asp:AsyncPostBackTrigger ControlID="gvSearch" />
</Triggers>
<ContentTemplate>
<test1uc:test1 ID="test1a" runat="server" />
</ContentTemplate>
</UpdatePanel>

Answer 1

What event do you want to use as trigger, the SelectedIndexChanged-event? Then apply the appropriate EventName.
<asp:AsyncPostBackTrigger ControlID="gvSearch" EventName="SelectedIndexChanged" />
However, that should already be the default event for GridView (see the remarks section).
Have a look at this thread: http://forums.asp.net/t/1136932.aspx
Update I think the best approach in your situation is to provide a custom event in your UserControl that is bubbled from the SelectedIndexChanged event from the GridView in the UC. Then you can use this event as AsyncPostBackTrigger for your UpdatePanel, e.g.:
<asp:AsyncPostBackTrigger ControlID="test1a" EventName="GridSearchClicked" />

Answer 2

Setting aside the fact that requiring access to a subcontrol is not good practice, here's my best suggestion...
Create a Public Sub in your user control as follows:
Private ParentUpdatePanel As System.Web.UI.UpdatePanel
' Must be called on every Page_Load!
Public Sub RegisterAsyncTrigger(MyScriptManager As System.Web.UI.ScriptManager, MyUpdatePanel As System.Web.UI.UpdatePanel)
MyScriptManager.RegisterAsyncPostBackControl(gvSearch)
ParentUpdatePanel = MyUpdatePanel
End Sub
On the Page_Load event, you'd call the function as follows:
Protected Sub Page_Load(Sender As Object, e As EventArgs)
' Call our new function, passing in the current ScriptManager and the UpdatePanel
' The ScriptManager handles the asynchronous postbacks
' The UpdatePanel handles the dynamic updates
test1.RegisterAsyncTrigger(ScriptManager.GetCurrent(Me), pnlSearch)
End Sub
In the event handler inside the gvSearch GridView control which must update the panel would contain the following code:
ParentUpdatePanel.Update()