php - Update XML node attribute -

i'm trying following without success. can me out why attribute imageid not changed?

$dom = new domdocument; $dom->loadxml($appcom_file_name); $frames = $dom->getelementsbytagname('frame'); foreach ($frames $frame) {     if ($frame->getattribute('imageid') == '') {         $frame->setattribute('imageid', $id);     }  }  $dom->savexml(); 

xml source:

<template>     <appcom>         <page>             <defaultvalues>                 <frame id="frame_01_0" deltarotation="0" deltascale="100" deltax="0" deltay="0" imageid="" />                 <frame id="frame_02_0" deltarotation="0" deltascale="100" deltax="0" deltay="0" imageid="" />                 <frame id="frame_03_0" deltarotation="0" deltascale="100" deltax="0" deltay="0" imageid="" />             </defaultvalues>         </page>         <page>             <defaultvalues>                 <frame id="frame_01_1" deltarotation="0" deltascale="100" deltax="0" deltay="0" imageid="" />                 <frame id="frame_02_1" deltarotation="0" deltascale="100" deltax="0" deltay="0" imageid="" />                 <frame id="frame_03_1" deltarotation="0" deltascale="100" deltax="0" deltay="0" imageid="" />             </defaultvalues>         </page>     </appcom> </template> 

i tested code , obviously, i'm getting error $id not defined. have tried changing line:

$frame->setattribute('imageid', $id); 

to this:

$frame->setattribute('imageid', $frame->getattribute('id')); 

?

and of course, print results screen use echo:

echo $dom->savexml();