我想在我的footer.php （稍后我会将其转换为插件），将两个表单字段发送到自定义表(wp_newsletter). 我已经在正确地发送表单并将其写入表中，但我不知道如何将成功或失败消息发送回用户。我当前的代码如下：

<form method="post">
  <input type="text" name="user_name">Name
  <input type="text" name="user_email">Email
  <input type="submit">
  <?php echo $message;  ?>
</form>

<?php
global $wpdb;
$table   = $wpdb->prefix . "newsletter";
$name    = sanitize_text_field( $_POST["user_name"] );
$email   = sanitize_email( $_POST["user_email"] );
$message = "";


if( isset($_POST["submit"]) ) {
  if ( is_email($email) && isset($name)) {
    if ( $wpdb->insert( $table, array("name"  => $name, "email" => $email)) != false ) {
      $message = "Your subscription was sent.";
    }
  }
  else {
    if ( !is_email($email) ) {
        $message = "Invalid email address.";
    } elseif ( !isset($name) ) {
        $message = "The field name is mandatory.";
    } else {
        $message = "Both name and email fields are mandatory.";
    }
  }
} else {
    $message = "Please, try again later.";
}
?>


<?php wp_footer(); ?>

</body>
</html>

如果无法插入行，此函数将返回false。否则，它将返回受影响的行数（始终为1）。