Where is Featured Image code stored in WP?

3 comments

1. Markup of that metabox is generated by _wp_post_thumbnail_html() function, contained in wp-admin/includes/post.php.

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2. Some handy links for you:

   • http://codex.wordpress.org/Post_Thumbnails
   • http://codex.wordpress.org/Function_Reference/get_the_post_thumbnail
   • http://codex.wordpress.org/Function_Reference/the_post_thumbnail
   • http://codex.wordpress.org/Function_Reference/has_post_thumbnail

   Those are useful if you’re wanting to display or act differently in the theme, based on the featured image.

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3. Here is a complete example to have the Featured image meta box display and work outside the wp-admin/post.php page context (since WordPress 4.6, see wp-admin/includes/post.php), which is one of the possible reason why you might want to know where is the code stored:

   /**
    * Featured image metabox
    *
    * @uses _wp_post_thumbnail_html
    *
    * @param int    $post_id   Post ID.
    * @param string $post_type Post type.
    */
   function featured_image_metabox( $post_id, $post_type ) {
   
       // @see edit-form-advanced.php
       $thumbnail_support = current_theme_supports( 'post-thumbnails', $post_type ) && post_type_supports( $post_type, 'thumbnail' );
   
       if ( ! $thumbnail_support ||
           ! current_user_can( 'upload_files' ) ) {
   
           return;
       }
   
       // All meta boxes should be defined and added before the first do_meta_boxes() call (or potentially during the do_meta_boxes action).
       require_once ABSPATH . 'wp-admin/includes/meta-boxes.php';
   
       if ( ! $post_id ) {
           // New post.
           $post = get_default_post_to_edit( $post_type, true );
   
           // Fix PHP error. Add filter so get_post( $post ) returns our post!
           $post->filter = 'raw';
       } else {
           $post = get_post( $post_id );
       }
   
       $thumbnail_id = get_post_meta( $post->ID, '_thumbnail_id', true );
   
       if ( ! $thumbnail_id ) {
   
           $thumbnail_id = -1;
       }
   
       $post_type_object = get_post_type_object( $post_type );
   
       $title = $post_type_object->labels->featured_image;
       ?>
       <script>
           jQuery( document ).ready(function( e ) {
               wp.media.view.settings.post.id = <?php echo json_encode( $post->ID ); ?>;
               wp.media.view.settings.post.featuredImageId = <?php echo json_encode( $thumbnail_id ); ?>;
               wp.media.view.settings.post.nonce = <?php echo json_encode( wp_create_nonce( 'update-post_' . $post->ID ) ); ?>;
           });
       </script>
       <div id="poststuff" style="min-width: 320px;">
           <div id="postimagediv" class="postbox">
               <h2 class='hndle'><span><?php echo esc_html( $title ); ?></span></h2>
               <div class="inside">
               <?php
                   echo _wp_post_thumbnail_html( $thumbnail_id, $post );
               ?>
               </div>
           </div>
       </div>
       <?php
   }
   

   

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