Strange Problem when Handling xml using DOM ,PHP

I want to handle a xml like this:

<GeocodeResponse> 
 <status>OK</status> 
 <result> 
  <type>street_address</type> 
  <address_component> 
   <long_name>Beijing</long_name> 
   <short_name>Beijing</short_name> 
   <type>locality</type> 
   <type>political</type> 
  </address_component> 
  <address_component> 
   <long_name>Beijing</long_name> 
   <short_name>Beijing</short_name> 
   <type>administrative_area_level_1</type>
   <type>political</type> 
  </address_component>  
 </result> 
</GeocodeResponse>

what I wanna do is loop the node under < address_component >

when using this :

$doc = new DOMDocument();
$doc->loadXML($contents);

$addresses=$doc->getElementsByTagName("address_component");

foreach($addresses as $address){

    $nodes = $address->$childNodes; //error arise here

    for($i=0;$i<count($nodes);$i++){
        //do work
    }

}

It always show :

    Fatal error: Cannot access empty property in C:\xampp\htdocs\read.php on line

$nodes = $address->$childNodes;

while it works fine with the code below :

        $doc = new DOMDocument();
        $doc->loadXML($contents);

        $addresses开发者_如何学Go=$doc->getElementsByTagName("address_component");
        for($k=0;$k<$addresses->length;$k++){
        $type_elements = $addresses->item($k)->getElementsByTagName('type');

            //do work        
        } 

I can not see the difference between these two method,in the first example,when I do the 'foreach' ,the $address I get is a single < address_component > element like this:

  <address_component> 
   <long_name>Beijing</long_name> 
   <short_name>Beijing</short_name> 
   <type>administrative_area_level_1</type>
   <type>political</type> 
  </address_component> 

right?

and of course it has $childNodes like < long_name >,< short_name >,etc.

but why I get empty property ?

Since you want to access a property, it should be childNodes without the $

$nodes = $address->childNodes;

When you put the $ in front, PHP will try to evaluate it as a variable.

_{On a sidenote, you seem to have error_reporting disabled or set too low, otherwise you would have seen the notice telling you Notice: Undefined variable: childNodes. You should set error_reporting(-1) on development machines to enable all errors.}