代码如下:

<?php 

//Put this in functions.php 

function get_primary_image($id, $size){ 
$featured = wp_get_attachment_image_src( get_post_thumbnail_id($id), $size, false); 
if($featured){ 
$childURL = $featured['0']; 
}else{ 
$children = get_children(array('post_parent' => $id, 'post_type' => 'attachment', 'post_mime_type' => 'image', 'numberposts' => 1)); 
reset($children); 
$childID = key($children); 
//$childURL = wp_get_attachment_url($childID); 
$childArray = wp_get_attachment_image_src($childID, $size, false); 
$childURL = $childArray['0']; 
if(empty($childURL)){ 
$childURL = get_bloginfo('template_url')."/images/default.png"; 
} 
} 
return($childURL); 
} 


//Run this in the loop (or any place you'd like - as long as you have an ID to feed it..) 
//First argument is the ID.. 
//Second argument is the size.. It'll handle 'large', 'medium', 'thumbnail' or even 

'array(100, 100)'.. 
get_primary_image(get_the_ID(), 'large'); 

?>