如何为wordpress后台添加文章缩略图？

if ( !function_exists('fb_AddThumbColumn') && function_exists('add_theme_support') ) {
// for post and page
add_theme_support('post-thumbnails', array( 'post', 'page' ) );
function fb_AddThumbColumn($cols) {
$cols['thumbnail'] = __('Thumbnail');
return $cols;
}
function fb_AddThumbValue($column_name, $post_id) {
$width = (int) 35;
$height = (int) 35;
if ( 'thumbnail' == $column_name ) {
// thumbnail of WP 2.9
$thumbnail_id = get_post_meta( $post_id, '_thumbnail_id', true );
// image from gallery
$attachments = get_children( array('post_parent' => $post_id, 'post_type' => 'attachment', 'post_mime_type' => 'image') );
if ($thumbnail_id)
$thumb = wp_get_attachment_image( $thumbnail_id, array($width, $height), true );
elseif ($attachments) {
foreach ( $attachments as $attachment_id => $attachment ) {
$thumb = wp_get_attachment_image( $attachment_id, array($width, $height), true );
}
}
if ( isset($thumb) && $thumb ) {
echo $thumb;
} else {
echo __('None');
}
}
}
// for posts
add_filter( 'manage_posts_columns', 'fb_AddThumbColumn' );
add_action( 'manage_posts_custom_column', 'fb_AddThumbValue', 10, 2 );
// for pages
add_filter( 'manage_pages_columns', 'fb_AddThumbColumn' );
add_action( 'manage_pages_custom_column', 'fb_AddThumbValue', 10, 2 );
}