UpdatePanel quits responding after Response.TransmitFile - asp.net

Question

I have a GridView in an UpdatePanel that shows a list of files. One of the columns in the GridView is a button that opens the listed PDF file.
<asp:UpdatePanel runat="server" ID="upPurchaseOrder">
<ContentTemplate>
<asp:GridView ID="gvPurachaseOrder" runat="server" AutoGenerateColumns="False" DataSourceID="odsPurchaseOrders"
EnableModelValidation="True" DataKeyNames="PurchaseOrderID,PromotionID" onrowcreated="gvPurachaseOrder_RowCreated">
<Columns>
<%--BoundFields omitted--%>
<asp:TemplateField ShowHeader="False">
<ItemTemplate>
<asp:Button ID="btnPurchaseOrderOpen" runat="server" Text="Open" CommandName="Open"
CommandArgument='<%# Eval("FilePath") %>' oncommand="btnPurchaseOrderOpen_Command" />
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
</ContentTemplate>
</asp:UpdatePanel>
In the RowCreated event I register btnPurchaseOrderOpen as a PostBack control, so it causes a full postback.
In the button event handler, I open the file with the Response.TransmitFile method.
Response.Clear();
Response.ContentType = GetConentTypeForFile(fi.Extension);
Response.AddHeader("content-disposition", String.Format("attachment;filename={0}", fi.Name));
Response.TransmitFile(fi.FullName);
Response.End();
My problem is that after the file is opened (it opens correctly) the UpdatePanel stops updating. I can click the other buttons and they never post back synchronously or asynchronously. I have a feeling the problem is related to the response, but I don't know how to fix it.

Answer 1

You are doing a full post back but you are not returning any new page to the server since you are only doing transmitfile and then response.end. It's basically a dead end for your page. The way you may want to get around this is to do the full post back in an iframe or simply create a direct link to the download file, even if that might be a ashx handler where you can continue to have similar logic to what you are already using.