php - 在一行代码上创建一个带有两个 wordpress 错误的元框

Question

下面的代码来自有关如何创建元框以将 PDF 上传到帖子或页面的教程。

add_action("admin_init", "pdf_init");
add_action('save_post', 'save_pdf_link');
function pdf_init(){
    add_meta_box("my-pdf", "PDF Document", "pdf_link", "post", "normal", "low");
    }
function pdf_link(){
    global $post;
    $custom  = get_post_custom($post->ID);
    $link    = $custom["link"][0];
    $count   = 0;
    echo '<div class="link_header">';
    $query_pdf_args = array(
        'post_type' => 'attachment',
        'post_mime_type' =>'application/pdf',
        'post_status' => 'inherit',
        'posts_per_page' => -1,
        );
    $query_pdf = new WP_Query( $query_pdf_args );
    $pdf = array();
    echo '<select name="link">';
    echo '<option class="pdf_select">SELECT pdf FILE</option>';
    foreach ( $query_pdf->posts as $file) {
       if($link == $pdf[]= $file->guid){
          echo '<option value="'.$pdf[]= $file->guid.'" selected="true">'.$pdf[]= $file->guid.'</option>';
         }else{
          echo '<option value="'.$pdf[]= $file->guid.'">'.$pdf[]= $file->guid.'</option>';
         }
        $count++;
    }
    echo '</select><br /></div>';
    echo '<p>Selecting a pdf file from the above list to attach to this post.</p>';
    echo '<div class="pdf_count"><span>Files:</span> <b>'.$count.'</b></div>';
}
function save_pdf_link(){
    global $post;
    if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE){ return $post->ID; }
    update_post_meta($post->ID, "link", $_POST["link"]);
}
add_action( 'admin_head', 'pdf_css' );
function pdf_css() {
    echo '<style type="text/css">
    .pdf_select{
        font-weight:bold;
        background:#e5e5e5;
        }
    .pdf_count{
        font-size:9px;
        color:#0066ff;
        text-transform:uppercase;
        background:#f3f3f3;
        border-top:solid 1px #e5e5e5;
        padding:6px 6px 6px 12px;
        margin:0px -6px -8px -6px;
        -moz-border-radius:0px 0px 6px 6px;
        -webkit-border-radius:0px 0px 6px 6px;
        border-radius:0px 0px 6px 6px;
        }
    .pdf_count span{color:#666;}
        </style>';
}
function pdf_file_url(){
    global $wp_query;
    $custom = get_post_custom($wp_query->post->ID);
    echo $custom['link'][0];
}

我尝试在本地安装它，但收到两个错误。

警告：C:\xampp\htdocs\meta\wp-content\themes\twentytwentyone\functions.php 中未定义的数组键“链接”

警告：尝试访问 C:\xampp\htdocs\meta\wp-content\themes\twentytwentyone\functions.php 中 null 类型值的数组偏移量

他们引用以下行

$link = $custom["link"][0];

所以我想看看有什么问题。

标签： phpwordpress