Question

In an ASP.NET 4.0 web application, I have a user control that is wrapped by an UpdatePanel (see the code below).

<asp:UpdatePanel ID="UpdatePanel5" runat="server" UpdateMode="Conditional">
    <ContentTemplate>
        <UC:MyCustomCtrl ID="customCtrl" runat="server" />
    </ContentTemplate>
</asp:UpdatePanel>

Obviously, this works great for every ASP.NET control that causes a postback in my user control because it makes it occur asynchronously. However, there is one process that this doesn’t work for!

I have an ASP.NET button (Create Report) in the user control that makes an asychronous request to the server. The server then creates an Excel spreadsheet and then places the spreadsheet in the HttpResponse to send back to the client’s browser so they can open/save it. However, it blows up at this point because the request to the server is asynchronous and apparently you can’t put a binary in the HttpResponse during an asynchronous request.

How do I get around this?

Answer 1

Register this button as synchronous postback control in user control’s Page_Load method: ScriptManager.GetCurrent(Page).RegisterPostBackControl(CreateReportButton);