C# ASP.NET Detect Download
<p>I am maintaining a website written in C# with ASP.NET. At the bottom of a page is an iframe. When a user clicks a button, the source for that iframe is set with Javascript to a page on the server.</p>

<pre><code>showLoadWidget();
document.getElementById("downloadFrame").src='SdrTrendDownload.aspx';
return false;
</code></pre>

<p>That page generates a file and allows the user to download it. Once the download file box pops up, I want to call <code>hideLoadWidget()</code> so the 'Loading Data...' overlay goes away. How do I detect when the download file box pops up?</p>
