How to find child page control while using postback trigger

Question

I am having one master page that has one update panel. Content place holder is within the update panel

Now i have child page which has a File upload control

To make work File upload control, i have to put Postback trigger.

But question is where i can put that Postback trigger ??

If i put Postback trigger in Master page than it will give me error that control does not found

and i can't put Postback trigger because child page has not other update panel

What is the solution for this problem ?

Answer 1

Simply wrap the FileUpload with an UpdatePanel , which don't do anything and hasn't any side effect but will solve the problem.

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <ContentTemplate>
        <asp:FileUpload ID="FileUpload1" runat="server" />
        <asp:Button ID="btnSubmit" runat="server" Text="Button" />
    </ContentTemplate>
    <Triggers>
        <asp:PostBackTrigger ControlID="btnSubmit" />
    </Triggers>
</asp:UpdatePanel>