我对插件开发相当陌生，但在编码方面有经验。我已经阅读了一些教程，并设法将我的帖子类型设置为幻灯片，但我想添加一个元框来放置URL。

然而，它并没有显示出来，我跟随的许多教程都说我现在应该看到它了。有人能帮忙吗？下面的教程、代码和图片链接。

后续教程：https://www.sitepoint.com/real-world-example-wordpress-plugin-development/

我也尝试过其他教程（来自：themefoundation and code.tutsplus），但它们似乎都不能与我已经编写的内容配合使用

（文本为荷兰语抱歉）

    <?php

function register_slide_content_type(){

    $labels = array(
        \'name\' => _x( \'Slides\', \'slideshow\' ),
        \'singular_name\' => _x( \'Slides\', \'slideshow\' ),
        \'add_new\' => _x( \'Nieuwe Slide\', \'slideshow\' ),
        \'add_new_item\' => _x( \'Nieuwe Slide Toevoegen\', \'slideshow\' ),
        \'edit_item\' => _x( \'Edit Slide\', \'slideshow\' ),
        \'new_item\' => _x( \'Nieuwe Slide\', \'slideshow\' ),
        \'view_item\' => _x( \'Bekijk Slide\', \'slideshow\' ),
        \'search_items\' => _x( \'Zoek Slides\', \'slideshow\' ),
        \'not_found\' => _x( \'Geen slides gevonden\', \'slideshow\' ),
        \'not_found_in_trash\' => _x( \'Geen slides gevonden in prullenbak\', \'slideshow\' ),
        \'parent_item_colon\' => _x( \'Parent Slide:\', \'slideshow\' ),
        \'menu_name\' => _x( \'Slideshow\', \'slideshow\' ),
    );

   //arguments for post type
       $args = array(
           \'labels\'            => $labels,
           \'hierarchical\' => true,
           \'description\' => \'Slides voor op de website\',
           \'taxonomies\' => array( \'plaatsen\' ),
           \'public\'            => true,
           \'publicly_queryable\'=> true,
           \'show_ui\'           => true,
           \'show_in_nav\'       => true,
           \'query_var\'         => true,
           \'supports\'          => array(\'title\',\'thumbnail\',\'editor\'),
           \'has_archive\'       => true,
           \'menu_position\'     => 5,
           \'show_in_admin_bar\' => true,
           \'menu_icon\'         => \'dashicons-images-alt2\',
           \'rewrite\'            => array(\'slug\' => \'slides\', \'with_front\' => \'true\')
       );

    register_post_type( \'slideshow\', $args );
}

add_action( \'init\', \'register_slide_content_type\' );

function plaatsen_taxonomy() {
    register_taxonomy(
        \'plaatsen\',
        \'slideshow\',
        array(
            \'hierarchical\' => true,
            \'label\' => \'Plaatsingen\',
            \'query_var\' => true,
            \'rewrite\' => array(
                \'slug\' => \'plaatsen\',
                \'with_front\' => false
            )
        )
    );
}
add_action( \'init\', \'plaatsen_taxonomy\');


add_action( \'load-post.php\', \'slide_post_meta_boxes_setup\' );
add_action( \'load-post-new.php\', \'slide_post_meta_boxes_setup\' );

function slide_post_meta_boxes_setup() {

  add_action( \'add_meta_boxes\', \'slide_add_post_meta_boxes\' );
}

function slide_add_post_meta_boxes() {
  add_meta_box(
    \'pukkemukslideshow\',      // Unique ID
    __( \'Slideshow\', \'example\' ),    // Title
    \'slide_post_class_meta_box\',   // Callback function
    \'post_type\',         // Admin page (or post type)
    \'advanced\',         // Context
    \'high\'         // Priority
  );
}


function slide_post_class_meta_box( $post ) { ?>
  <p>
    <label for="slide-post-class">Plak hier de URL waar de slide naar moet wijzen.</label>
    <br />
    <input type="text" name="slide-post-class" id="slide-post-class" value="<?php echo esc_attr( get_post_meta( $post->ID, \'slide_post_class\', true ) ); ?>" size="30" />
  </p>
<?php } 

?>