``` add_action('save_post', 'wpds_check_thumbnail'); add_action('admin_notices', 'wpds_thumbnail_error'); function wpds_check_thumbnail($post_id) { // change to any custom post type if(get_post_type($post_id) != 'post') return; if ( !has_post_thumbnail( $post_id ) ) { // set a transient to show the users an admin message set_transient( "has_post_thumbnail", "no" ); // unhook this function so it doesn't loop infinitely remove_action('save_post', 'wpds_check_thumbnail'); // update the post set it to draft wp_update_post(array('ID' => $post_id, 'post_status' => 'draft')); add_action('save_post', 'wpds_check_thumbnail'); } else { delete_transient( "has_post_thumbnail" ); } } function wpds_thumbnail_error() { // check if the transient is set, and display the error message if ( get_transient( "has_post_thumbnail" ) == "no" ) { echo "<div id='message' class='error'><p><strong>您必須選擇一個特色圖片，您的文章現已被保存，但是無法發布。</strong></p></div>"; delete_transient( "has_post_thumbnail" ); } } ```