I use a very rough plugin to add information about the artist and a URL to media files. It needs some tweaking (and I need the time), but it works and may demonstrate how add the extra fields and how to use them in your theme:
<?php
/*
Plugin Name: Media Artist Field
Description: Adds two field to attachments – Artist and Artist URL – and adds this information to captions.
Version: 0.1
Author: Fuxia Scholz
Created: 19.09.2010
*/
$Media_Artist = new Media_Artist(
array (
'artist_name' => array (
'public' => 'artist_name'
, 'hidden' => '_artist_name'
, 'label' => 'Fotograf (Name)'
)
, 'artist_url' => array (
'public' => 'artist_url'
, 'hidden' => '_artist_url'
, 'label' => 'Fotograf (URL)'
)
)
, 'Foto: '
);
/**
* Adds two fields for credits to any media file: name and URL.
*
* Based on the clear tutorial by Andy Blackwell:
* @link http://net.tutsplus.com/?p=13076
*/
class Media_Artist
{
public
$fields = array (
'artist_name' => array (
'public' => 'artist_name'
, 'hidden' => '_artist_name'
, 'label' => 'Artist Name'
)
, 'artist_url' => array (
'public' => 'artist_url'
, 'hidden' => '_artist_url'
, 'label' => 'Artist URL'
)
)
// Maybe its own field?
, $caption_prefix
, $br_before = TRUE;
public function __construct(
$fields = array()
, $caption_prefix = 'Source: '
, $br_before = TRUE
)
{
$this->fields = array_merge($this->fields, $fields);
$this->caption_prefix = $caption_prefix;
$this->br_before = (bool) $br_before;
$this->set_filter();
}
public function set_filter()
{
add_filter(
'attachment_fields_to_edit'
, array ( $this, 'add_fields' )
, 15
, 2
);
add_filter(
'attachment_fields_to_save'
, array ( $this, 'save_fields' )
, 10
, 2
);
add_filter(
'img_caption_shortcode'
, array ( $this, 'caption_filter' )
, 1
, 3
);
}
public function add_fields($form_fields, $post)
{
foreach ( $this->fields as $field)
{
$form_fields[ $field['public'] ]['label'] = $field['label'];
$form_fields[ $field['public'] ]['input'] = 'text';
$form_fields[ $field['public'] ]['value'] = get_post_meta(
$post->ID
, $field['hidden']
, TRUE
);
}
return $form_fields;
}
public function save_fields($post, $attachment)
{
foreach ( $this->fields as $field)
{
if ( isset ( $attachment[ $field['public'] ]) )
{
update_post_meta(
$post['ID']
, $field['hidden']
, $attachment[ $field['public'] ]
);
}
}
return $post;
}
public function caption_filter($empty, $attr, $content="")
{
/* Typical input:
*
* <a href="http://example.com/2008/images-test/albeo-screengrab/"
* rel="attachment wp-att-525"><img
* src="http://example.com/uploads/2010/08/albeo-screengrab4.jpg?w=300"
* alt="" title="albeo-screengrab" width="300" height="276"
* class="size-medium wp-image-525" /></a>The caption.
*/
extract(
shortcode_atts(
array (
'id' => ''
, 'align' => 'alignnone'
, 'width' => ''
, 'caption' => ''
, 'nocredits' => '0'
)
, $attr
)
);
// Let WP handle these cases.
if ( empty ($id ) or 1 == $nocredits )
{
return '';
}
if ( 1 > (int) $width || empty ( $caption ) )
{
return $content;
}
if ( ! empty ( $id ) )
{
// Example: attachment_525
$html_id = 'id="' . esc_attr($id) . '" ';
$tmp = explode('_', $id);
$id = end($tmp);
$sub_caption = '';
$artist_name = get_post_meta($id, $this->fields['artist_name']['hidden'], TRUE);
$artist_url = get_post_meta($id, $this->fields['artist_url']['hidden'], TRUE);
// Okay, at least one value.
if ( '' != $artist_name . $artist_url )
{
$sub_caption .= $this->br_before ? '<br />' : '';
$sub_caption .= '<span class="media-artist">' . $this->caption_prefix;
// No name given. We use the shortened URL.
if ( '' == $artist_name )
{
$sub_caption .= '<a rel="author" href="'
. $artist_url . '">'
. $this->short_url($artist_url)
. '</a>';
} // We have just the name.
elseif ( '' == $artist_url )
{
$sub_caption .= $artist_name;
} // We have both.
else
{
$sub_caption .= '<a rel="author" href="'
. $artist_url . '">'
. $artist_name
. '</a>';
}
$sub_caption .= '</span>';
}
$caption .= $sub_caption;
}
return '<div ' . $html_id . 'class="wp-caption ' . esc_attr($align)
. '" style="width: ' . (10 + (int) $width) . 'px">'
. do_shortcode( $content ) . '<p class="wp-caption-text">'
. $caption . '</p></div>';
}
public function short_url($url, $max_length=20)
{
$real_length = mb_strlen($url, 'UTF-8');
if ( $real_length <= $max_length )
{
return $url;
}
$keep = round( $max_length / 2 ) - 1;
return mb_substr($url, 0, $keep, 'UTF-8') . '…'
. mb_substr($url, -$keep, $real_length, 'UTF-8');
}
# @todo uninstall
}
