如何让initWithContentsOfURL等待动态生成的xml页面?

I am trying to send a query as part a the URL to obtain an XML file, and then trying to parse the XML file using NSXMLParser and initWithContentsOfURL. However the parser is not able to parse the file. I tested the parser with the same file, but this time the file was saved on the server (it was not being generated) and it worked just fine, so I know it is not a problem with the parser.I am trying to send a query as part a the URL t