The screenshots posted in that answer were created using the register_meta_box_cb
argument that is available to for custom post types.
register_meta_box_cb must specify a callback function that contains the code for the meta box.
To create the meta box you can use the WordPress built in add_meta_box function which also requires a function to save the entered data when the post is saved.
Here is some example code that I created to add 2 custom meta boxes to my portfolio post type I use on my personal website.
The "Projects" post type I created contained this argument:
'register_meta_box_cb' => 'c3m_project_meta',
The first function below is the call back function for register_meta_box_cb. The following 2 output the html for the meta boxes on the add post page and the last 2 save the entered data.
function c3m_project_meta() {
add_meta_box('_c3m_project_url', __('Enter Website Url') , 'c3m_project_url', 'project', 'side', 'low');
add_meta_box('_c3m_project_work', __('Enter Work Done on Project') , 'c3m_project_work', 'project', 'side', 'low');
}
function c3m_project_url($post) {
global $post;
echo '<input type="hidden" name="banner-buttonmeta_noncename" id="banner-buttonmeta_noncename" value="' .
wp_create_nonce( plugin_basename(__FILE__) ) . '" />';
$projecturl = get_post_meta($post->ID, '_projecturl', true);
echo '<input type="text" name="_projecturl" value="' . $projecturl . '" class="widefat" />' ;
}
function c3m_project_work($post) {
global $post;
echo '<input type="hidden" name="banner-buttonmeta_noncename" id="banner-buttonmeta_noncename" value="' .
wp_create_nonce( plugin_basename(__FILE__) ) . '" />';
$projectwork = get_post_meta($post->ID, '_projectwork', true);
echo '<input type="text" name="_projectwork" value="' . $projectwork . '" class="widefat" />' ;
}
add_action('admin_init', 'c3m_project_meta');
function c3m_save_project_meta( $post_id , $post ) {
if ( !wp_verify_nonce( $_POST [ 'banner-buttonmeta_noncename' ], plugin_basename( __FILE__ ) )) { return $post ->ID;
}
if ( !current_user_can( 'edit_post' , $post ->ID )) return $post ->ID;
$c3m_projecturl [ '_projecturl' ] = $_POST [ '_projecturl' ];
foreach ( $c3m_projecturl as $key => $value ) {
if ( $post ->post_type == 'revision' ) return ;
$value = implode( ',' , ( array ) $value );
if (get_post_meta( $post ->ID, $key , FALSE)) {
update_post_meta( $post ->ID, $key , $value ); } else {
add_post_meta( $post ->ID, $key , $value ); } if (! $value ) delete_post_meta( $post ->ID, $key );
}
$c3m_projectwork [ '_projectwork' ] = $_POST [ '_projectwork' ];
foreach ( $c3m_projectwork as $key => $value ) {
if ( $post ->post_type == 'revision' ) return ;
$value = implode( ',' , ( array ) $value );
if (get_post_meta( $post ->ID, $key , FALSE)) {
update_post_meta( $post ->ID, $key , $value ); } else {
add_post_meta( $post ->ID, $key , $value ); } if (! $value ) delete_post_meta( $post ->ID, $key );
}
}
add_action( 'save_post' , 'c3m_save_project_meta' , 1, 2);