Check if an xml is loaded with simplexml_load_string - php

Question

I am querying an xml file with php like this :
public function trackOrderAction()
{
$request = Mage::getResourceModel( 'order/request' );
$request->setOrder($this->getRequest()->getParam('increment_id'));
$response = $request->submit(true);
$xml = simplexml_load_string($response);
$items = count($xml->OrderItems->OrderItem);
}
The xml is not ready immediately so if people try to use the function before it is ready there is an error because it is trying to get the property of a non-object. My question is what is the proper way to check the xml response to see if there is anything and stop the function if there is not?
I tried something simple like
if (empty($xml)){
die();
} else {
$items = count($xml->OrderItems->OrderItem);
}
But this does not help. Any ideas on how to check to see if the xml loaded?

Answer 1

From http://us.php.net/manual/en/function.simplexml-load-string.php
Returns an object of class SimpleXMLElement with properties containing
the data held within the xml document. On errors, it will return
FALSE.
public function trackOrderAction()
{
$request = Mage::getResourceModel( 'order/request' );
$request->setOrder($this->getRequest()->getParam('increment_id'));
$response = $request->submit(true);
$xml = simplexml_load_string($response);
if ( !$xml ) {
return false;
}
$items = count($xml->OrderItems->OrderItem);
}
It will return false if there was an error. So fail right away if simplexml_load_string fails and return false. Otherwise continue on with the rest of the function. Never die() in a function.