title: WordPress Meta Box for custom post type
body: <p>I have a custom post type ("site") that I'm using to display our clients, and I am trying to add a custom meta box to the add/edit site page. I'm using the sample from the WordPress codex (<a href="http://codex.wordpress.org/Function_Reference/add_meta_box" rel="nofollow">http://codex.wordpress.org/Function_Reference/add_meta_box</a>) and I'm able to get the title of the meta box to show up in the add/edit site page, but there's no text box to enter the website URL. </p>
  
  <p>Here is the code I have:</p>
  
  <pre><code>&lt;?php
  
  // Add the Meta Box
  /* function nw_add_custom_meta_box() {
      add_meta_box(
          'website', // $id
          'Website', // $title 
          'show_custom_meta_box', // $callback
          'site', // $page
          'normal', // $context
          'high'); // $priority
  }
  add_action('add_meta_boxes', 'nw_add_custom_meta_box');
  */
  
  
  /**
   * Adds a box to the main column on the Post and Page edit screens.
   */
  function nw_add_custom_meta_box() {
  
      $screens = array( 'site' ); // add items to add to multiple post types
  
      foreach ( $screens as $screen ) {
          add_meta_box(
          'website', // $id
          'Website', // $title 
          'show_custom_meta_box', // $callback
          $screen, // $page
          'normal', // $context
          'high' // $priority
          );
      }
  }
  add_action( 'add_meta_boxes', 'nw_add_custom_meta_box' );
  
  /**
   * Prints the box content.
   * 
   * @param WP_Post $post The object for the current post/page.
   */
  function myplugin_meta_box_callback( $post ) {
  
      // Add an nonce field so we can check for it later.
      wp_nonce_field( 'website', 'website_nonce' );
  
      /*
       * Use get_post_meta() to retrieve an existing value
       * from the database and use the value for the form.
       */
      $value = get_post_meta( $post-&gt;ID, '_website', true );
  
      echo '&lt;label for="website"&gt;';
      _e( 'Website Address', 'myplugin_textdomain' );
      echo '&lt;/label&gt; ';
      echo '&lt;input type="text" id="website" name="website" value="' . esc_attr( $value ) . '" size="25" /&gt;';
  }
  
  /**
   * When the post is saved, saves our custom data.
   *
   * @param int $post_id The ID of the post being saved.
   */
  function nuggetweb_save_meta_box_data( $post_id ) {
  
      /*
       * We need to verify this came from our screen and with proper authorization,
       * because the save_post action can be triggered at other times.
       */
  
      // Check if our nonce is set.
      if ( ! isset( $_POST['website_nonce'] ) ) {
          return;
      }
  
      // Verify that the nonce is valid.
      if ( ! wp_verify_nonce( $_POST['website_nonce'], 'website' ) ) {
          return;
      }
  
      // If this is an autosave, our form has not been submitted, so we don't want to do anything.
      if ( defined( 'DOING_AUTOSAVE' ) &amp;&amp; DOING_AUTOSAVE ) {
          return;
      }
  
      // Check the user's permissions.
      if ( isset( $_POST['post_type'] ) &amp;&amp; 'page' == $_POST['post_type'] ) {
  
          if ( ! current_user_can( 'edit_page', $post_id ) ) {
              return;
          }
  
      } else {
  
          if ( ! current_user_can( 'edit_post', $post_id ) ) {
              return;
          }
      }
  
      /* OK, it's safe for us to save the data now. */
  
      // Make sure that it is set.
      if ( ! isset( $_POST['website'] ) ) {
          return;
      }
  
      // Sanitize user input.
      $my_data = sanitize_text_field( $_POST['website'] );
  
      // Update the meta field in the database.
      update_post_meta( $post_id, '_website', $my_data );
  }
  add_action( 'save_post', 'nuggetweb_save_meta_box_data' );
  
  ?&gt;
  </code></pre>