title: add querystring to a postbackurl property of asp:button
body: <p>I've got a textbox and a button on a form on default.aspx and in my DownloadHandler.ashx I am getting the value I need from HttpContext.Request.Form("txtURI"):</p>
  
  <pre><code>            &lt;asp:TextBox ID="txtURI"
                          AutoPostBack="true"
                          runat="server"&gt;&lt;/asp:TextBox&gt;
              &lt;asp:Button ID="DownloadButton"
                          PostBackUrl="~/DownloadHandler.ashx" 
                          runat="server" 
                          Text="Download"/&gt;
  </code></pre>
  
  <p>I would like to change it so that the value typed into the textbox gets passed to the DownloadHandler.ashx as a querystring (instead of picking it out of the Request.Form). </p>
  
  <p>What is the best way to accomplish that?</p>