WordPress函数wp_get_attachment_url()用法 获取附件URL网址

描述：

返回附件(特色图像/文件)URL网址

用法：

<?php wp_get_attachment_url( $id ); ?>

参数：

$id

(integer) (必填) 所需附件的ID

默认值: None

示例：

if ( have_posts() ) : while ( have_posts() ) : the_post();
if ( has_post_thumbnail() ) {
$feat_image_url = wp_get_attachment_url( get_post_thumbnail_id() );
echo '<div style="background-image:url('.$feat_image_url.');"></div>';
}
endwhile;endif;

源文件：

/**
* Retrieve the URL for an attachment.
*
* @since 2.1.0
*
* @global string $pagenow
*
* @param int $post_id Optional. Attachment ID. Default 0.
* @return string|false Attachment URL, otherwise false.
*/
function wp_get_attachment_url( $post_id = 0 ) {
$post_id = (int) $post_id;
if ( !$post = get_post( $post_id ) )
return false;

if ( 'attachment' != $post->post_type )
return false;

$url = '';
// Get attached file.
if ( $file = get_post_meta( $post->ID, '_wp_attached_file', true) ) {
// Get upload directory.
if ( ($uploads = wp_upload_dir()) && false === $uploads['error'] ) {
// Check that the upload base exists in the file location.
if ( 0 === strpos( $file, $uploads['basedir'] ) ) {
// Replace file location with url location.
$url = str_replace($uploads['basedir'], $uploads['baseurl'], $file);
} elseif ( false !== strpos($file, 'wp-content/uploads') ) {
$url = $uploads['baseurl'] . substr( $file, strpos($file, 'wp-content/uploads') + 18 );
} else {
// It's a newly-uploaded file, therefore $file is relative to the basedir.
$url = $uploads['baseurl'] . "/$file";
}
}
}

/*
* If any of the above options failed, Fallback on the GUID as used pre-2.7,
* not recommended to rely upon this.
*/
if ( empty($url) ) {
$url = get_the_guid( $post->ID );
}

// On SSL front-end, URLs should be HTTPS.
if ( is_ssl() && ! is_admin() && 'wp-login.php' !== $GLOBALS['pagenow'] ) {
$url = set_url_scheme( $url );
}

/**
* Filter the attachment URL.
*
* @since 2.1.0
*
* @param string $url URL for the given attachment.
* @param int $post_id Attachment ID.
*/
$url = apply_filters( 'wp_get_attachment_url', $url, $post->ID );

if ( empty( $url ) )
return false;

return $url;
}