致命错误：在非对象上调用成员函数 getElementsByTagName()

Question

<?php 
$q=$_GET["q"];
$xml = $q;
$xmlDoc = new DOMDocument();
$xmlDoc->load($xml);
$channel=$xmlDoc->getElementsByTagName('channel')->item(0);
$channel_title = $channel->getElementsByTagName('title')
->item(0)->childNodes->item(0)->nodeValue;
$channel_desc = $channel->getElementsByTagName('description')
->item(0)->childNodes->item(0)->nodeValue;
echo("<b> $channel_title </b>" );
echo("<br>");
echo($channel_desc . "</p>");
$x=$xmlDoc->getElementsByTagName('item');
$i=0;
while($i<=9)
  {
  $i++;
  $item_title=$x->item($i)->getElementsByTagName('title')
  ->item(0)->childNodes->item(0)->nodeValue;
  $item_desc=$x->item($i)->getElementsByTagName('description')
  ->item(0)->childNodes->item(0)->nodeValue;
  echo ("<b> $item_title </b>"  );
  echo ("<br>");
  echo ($item_desc . "</p>"); 
  }
?>

I get this error :

Fatal error: Call to a member function getElementsByTagName() on a non-object in C:\\Program Files (x86)\\EasyPHP-DevServer-14.1VC11\\data\\localweb\\v9\\naloga2.php on line 19.

I get this error when there are less than 10 items in RSS.

Answer 1

You have while($i<=9) then you ask for each element, 0-9. So when you don't have 10 elements, $x->item($i) returns nothing, and thus calling ->getElementsByTagName('title') gives an error since you're calling the method on nothing.

You want to restructure to this:

<?php 
$q=$_GET["q"];
$xml = $q;
$xmlDoc = new DOMDocument();
$xmlDoc->load($xml);
$channel=$xmlDoc->getElementsByTagName('channel')->item(0);
$channel_title = $channel->getElementsByTagName('title')->item(0)->childNodes->item(0)->nodeValue;
$channel_desc = $channel->getElementsByTagName('description')->item(0)->childNodes->item(0)->nodeValue;
echo("<b> $channel_title </b>" );
echo("<br>");
echo($channel_desc . "</p>");
$x=$xmlDoc->getElementsByTagName('item');

$counter = 0 ;
foreach($x as $item)
  {
      if(++$counter > 9) break;
      $item_title=$item->getElementsByTagName('title')->item(0)->childNodes->item(0)->nodeValue;
      $item_desc=$item->getElementsByTagName('description')->item(0)->childNodes->item(0)->nodeValue;
      echo ("<b> $item_title </b>"  );
      echo ("<br>");
      echo ($item_desc . "</p>"); 
  }
?>

Answer 2

Suppose there are 8 items. Your code

$i=0;
while($i<=9) {
  $i++;
  ...
}

iterates up to i === 10. Therefore this code

$item_title = $x->item($i)

doesn't return an element - since the last element has an index of 7 [valid 0 .. 7].

Try this:

  for( $i=0; $i < $x->length; $i++ ) {
    ...
  }