Global custom meta box

Question

I am trying to create a custom meta box for multiple custom post types in WordPress without creating duplicate code.

Currently I have:

add_meta_box('adv_form_box1', 'Advanced Form', 'adv_form1', 'custom-post-type1', 'side', 'high');
add_meta_box('adv_form_box2', 'Advanced Form', 'adv_form2', 'custom-post-type2', 'side', 'high');
add_meta_box('adv_form_box3', 'Advanced Form', 'adv_form3', 'custom-post-type3', 'side', 'high');

function adv_form1() {
global $post;
$custom = get_post_custom($post->ID);
$filename = $custom['filename'][0]; ?>
<label>Filename:</label> (this field is required)<br/><input name="filename" size="70" value="<?php echo $filename; ?>" />
<?php }

function adv_form2() {
global $post;
$custom = get_post_custom($post->ID);
$filename = $custom['filename'][0]; ?>
<label>Filename:</label> (this field is required)<br/><input name="filename" size="70" value="<?php echo $filename; ?>" />
<?php }

function adv_form3() {
global $post;
$custom = get_post_custom($post->ID);
$filename = $custom['filename'][0]; ?>
<label>Filename:</label> (this field is required)<br/><input name="filename" size="70" value="<?php echo $filename; ?>" />
<?php }

I feel as though I am creating a bunch of extra un-needed code. Is there anyway to set the meta box as "global" to be used in all post-types?

Answer 1

In addition to the other answers, you can further improve it by looping through an array of types instead of manually adding a new add_meta_box() line each time you add a new type.

$postTypes = array( 'custom-post-type1', 'custom-post-type2', 'custom-post-type3' );
foreach( $postTypes as $pt )
    add_meta_box( 'adv_form_box1', 'Advanced Form', 'adv_form1', $pt, 'side', 'high' );

Answer 2

You are creating a bunch of extra work.

Rather than creating a separate callback function for each post type, just use the same callback. So:

add_meta_box('adv_form_box', 'Advanced Form', 'adv_form', 'custom-post-type1', 'side', 'high');
add_meta_box('adv_form_box', 'Advanced Form', 'adv_form', 'custom-post-type2', 'side', 'high');
add_meta_box('adv_form_box', 'Advanced Form', 'adv_form', 'custom-post-type3', 'side', 'high');

function adv_form() {
    global $post;
    $custom = get_post_custom($post->ID);
    $filename = $custom['filename'][0]; 
?>
<label>Filename:</label> (this field is required)<br/><input name="filename" size="70" value="<?php echo $filename; ?>" />
<?php 
}

Answer 3

Yes! You can use the same callback function:

add_meta_box('adv_form_box1', 'Advanced Form', 'adv_form1', 'custom-post-type1', 'side', 'high');
add_meta_box('adv_form_box2', 'Advanced Form', 'adv_form1', 'custom-post-type2', 'side', 'high');
add_meta_box('adv_form_box3', 'Advanced Form', 'adv_form1', 'custom-post-type3', 'side', 'high');

(I've kept the IDs the same, but these could be identical for each post type too).