The youtube API sometimes throws error: Call to a member function children() on a non-object - youtube-api

Question

When i launch the php script, sometime works fine, but many other times it retrieve me this errror
Fatal error: Call to a member function children() on a non-object in
/membri/americanhorizon/ytvideo/rilevametadatadaurlyoutube.php on line
21
This is the first part of the code
// set feed URL
$feedURL = 'http://gdata.youtube.com/feeds/api/videos/dZec2Lbr_r8';
// read feed into SimpleXML object
$entry = simplexml_load_file($feedURL);
$video = parseVideoEntry($entry);
function parseVideoEntry($entry) {
$obj= new stdClass;
// get nodes in media: namespace for media information
$media = $entry->children('http://search.yahoo.com/mrss/'); //<----this is the doomed line 21
UPDATE: solution adopted
for ($i=0 ; $i< count($fileArray); $i++)
{
// set feed URL
$feedURL = 'http://gdata.youtube.com/feeds/api/videos/'.$fileArray[$i];
// read feed into SimpleXML object
$entry = simplexml_load_file($feedURL);
if (is_object($entry))
{
$video = parseVideoEntry($entry);
echo ($video->description."|".$video->length);
echo "<br>";
}
else
{
$i--;
}
}
In this mode i force the script to re-check the file that caused the error

Answer 1

You are first of all calling a function:
$entry = simplexml_load_file($feedURL);
That function has a return value. You find it documented on the manual page of that function:
http://php.net/simplexml_load_file
Then you use that return value in form of a variable $entry without verifying that the function call was successful.
Because of that, you run into an error next. However your error/mistake is how you treat the return value of the function.
Not dealing with return values properly is like calling for trouble. Read about the function you use, check the return value(s) and proceed according to success or error conditions.
$entry = simplexml_load_file($feedURL);
if (FALSE === $entry)
{
// youtube not available.
}
else
{
// that's what I love!
}

Answer 2

Sometimes? Really?
Take a look at this:
<?php
$dummy; //IN FACT, this var is NULL now
// Will throw exactly the same error you get
$dummy->children();
Why? Because, we can call method from an object type.
So, if you wanna avoid errors like this one, next time you would call the method ensure that it's "possible".
<?php
if ( is_object($dummy) && method_exists($dummy, 'children') ){
//sure it works
$dummy->children();
}