Guide to Wordpress's Custom Write Panels

WordPress 3.0 ushered in significant updates, including the integration of WordPress MU (enabling multi-site management) and the introduction of custom post types. A particularly useful feature enhanced by custom post types is the Custom Write Panel.

Custom Write Panels provide customizable form fields (text inputs, checkboxes, etc.) within the post editor, linked to custom fields. While the default Custom Field Panel is available, it can be cumbersome for extensive data entry. Custom Write Panels offer a streamlined, visually appealing alternative.

Let's illustrate with a "Books" custom post type. Beyond the standard title and content, we'll add "Author" and "ISBN" fields. In your theme's functions.php, add this code to register the custom post type:

<code class="language-php">add_action( 'init', 'create_book_type' );
function create_book_type() {
  register_post_type( 'books', array(
    'labels' => array(
      'name' => __( 'Books' ),
      'singular_name' => __( 'Book' )
    ),
    'public' => true,
  ) );
}</code>

This registers the "Books" post type. Next, add the following to functions.php to create the Custom Write Panel:

<code class="language-php">// Define paths (adjust as needed)
define( 'MY_WORDPRESS_FOLDER', $_SERVER['DOCUMENT_ROOT'] );
define( 'MY_THEME_FOLDER', str_replace("\",'/',dirname(__FILE__)) );
define( 'MY_THEME_PATH', '/' . substr( MY_THEME_FOLDER, stripos(MY_THEME_FOLDER,'wp-content') ) );

add_action('admin_init','book_meta_init');
function book_meta_init() {
  wp_enqueue_style( 'my_meta_css', MY_THEME_PATH . '/custom/book_panel.css' );
  add_meta_box( 'book_meta', 'Book Information', 'book_meta', 'books', 'advanced', 'high' );
}

function book_meta() {
  global $post;
  $author = get_post_meta($post->ID,'author',TRUE);
  $isbn = get_post_meta($post->ID,'isbn',TRUE);
  include(MY_THEME_FOLDER . '/custom/book_information.php');
  wp_nonce_field( __FILE__, 'my_meta_noncename' );
}

function my_meta_save($post_id) {
  if (!wp_verify_nonce( $_POST['my_meta_noncename'], __FILE__ )) return $post_id;
  if (!current_user_can('edit_post', $post_id)) return $post_id;
  $accepted_fields['books'] = array( 'author', 'isbn' );
  $post_type_id = $_POST['post_type'];
  foreach ($accepted_fields[$post_type_id] as $key) {
    $custom_field = $_POST[$key];
    if (is_null($custom_field)) delete_post_meta($post_id, $key);
    elseif (isset($custom_field) && !is_null($custom_field)) update_post_meta($post_id,$key,$custom_field);
  }
  return $post_id;
}
add_action('save_post','my_meta_save');</code>

Create a custom directory in your theme and add book_panel.css (for styling) and book_information.php (for the panel HTML).

book_panel.css:

<code class="language-css">.book_panel .description { display: none; }
.book_panel label { display: block; font-weight: bold; margin: 6px; margin-bottom: 0; margin-top: 12px; }
.book_panel label span { display: inline; font-weight: normal; }
.book_panel span { color: #999; display: block; }
.book_panel textarea, .book_panel input[type='text'] { margin-bottom: 3px; width: 100%; }
.book_panel h4 { color: #999; font-size: 1em; margin: 15px 6px; text-transform:uppercase; }</code>

book_information.php:

<code class="language-php"><div class="book_panel">
  <h4>Book Details</h4>
  <label for="author">Author <span>(Required)</span></label>
  <input type="text" name="author" id="author" value="<?php echo esc_attr( $author ); ?>"><br>
  <label for="isbn">ISBN <span>(Required)</span></label>
  <input type="text" name="isbn" id="isbn" value="<?php echo esc_attr( $isbn ); ?>">
</div></code>

Finally, to display the custom fields in your theme, use get_post_meta() within your loop:

<code class="language-php">$loop = new WP_Query( array( 'post_type' => 'books', 'posts_per_page' => 10 ) );
while ($loop->have_posts()) : $loop->the_post();
  the_title();
  the_content();
  echo 'Author: ' . get_post_meta(get_the_ID(), "author", true);
  echo 'ISBN: ' . get_post_meta(get_the_ID(), "isbn", true);
endwhile;</code>

This completes the setup. Remember to adjust paths in the code to match your theme's structure. For more in-depth WordPress knowledge, consider our publication, "Build Your Own Wicked WordPress Themes."

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