我实现了一个简单的类，如：

class my_form {

        private $error_message;

        function __construct()
        {
            add_shortcode(\'my_form_custom\', array($this, \'show_custom_form\'));
        }

        function registration_template_form() {
        ?>              
            <div class="popup_canvas_container">            
                <form id="my_form" class="my_form" method="post" action="<?php echo esc_url($_SERVER[\'REQUEST_URI\']); ?>">
                    <p><label for="first_field">Field1:</label>&nbsp;<input type="text" name="first_field" id="first_field" value="<?php echo(isset($_POST[\'first_field\']) ? $_POST[\'first_field\'] : null); ?>" required /></p>
                    [...]
                    <div class="confirmation_box">
                        <p><button name="post_form" id="post_form" type="submit"><?php _e(\'Submit\', \'my_form_textdomain\'); ?></button></p>                      
                    </div>
                </form>
                <div id="messages_box" class="messages_box">
                    <p><div id="message_label"></div></p>
                </div>              
            </div>          
            
        <?  
        }                   
                    
        function form_validation() {
            if ( strlen($this->first_field) < 4 ) { 
                $error_message = \'Too short!\';
                return false;
            }
        }
                    
        function save_to_db() {         
            if ( !$this->form_validation() ) {
                ?>                   
                    <script language="javascript">$("#message_label").text("<?php echo $error_message; ?>"); $(\'#messages_box\').dialog();</script>
                <?php
            } else {    
            }
        }
                    
        function show_custom_form() {
            ob_start():
            
            if (isset($_POST[\'post_form\'])) {
                $this->save_to_db();
            }
            
            $this->show_template_form();
            
            return ob_get_clean();
        }
}

而且，就像我在Google上几乎到处都能找到的一样，用jquery将内容的变量传递给消息框div，我只是做了一个回显，然后我应该显示错误消息，显示一个对话框消息。但我一直在控制台日志中记录此错误：

<script language="javascript">$("#message_label").text("<br />
<b>Notice</b>:  Undefined variable: error_message in <b>..../my_form.php</b> on line <b>108</b><br />
"); $(\'#messages_box\').dialog();</script>

此时，将变量的内容传递给div的正确方法是什么？提前感谢！干杯，路易吉

编辑：如果我使用传递函数值实现，如下所示：

class my_form {

        private $first_field;
        public $error_message;      

        function __construct()
        {
            add_shortcode(\'my_form_custom\', array($this, \'show_custom_form\'));
        }

        function registration_template_form() {
        ?>              
            <div class="popup_canvas_container">            
                <form id="my_form" class="my_form" method="post" action="<?php echo esc_url($_SERVER[\'REQUEST_URI\']); ?>">
                    <p><label for="first_field">Field1:</label>&nbsp;<input type="text" name="first_field" id="first_field" value="<?php echo(isset($_POST[\'first_field\']) ? $_POST[\'first_field\'] : null); ?>" required /></p>
                    [...]
                    <div class="confirmation_box">
                        <p><button name="post_form" id="post_form" type="submit"><?php _e(\'Submit\', \'my_form_textdomain\'); ?></button></p>                      
                    </div>
                </form>
                <div id="messages_box" class="messages_box">
                    <p><div id="message_label"></div></p>
                </div>              
            </div>          
            
        <?  
        }                   
                    
        function form_validation() {
            if ( strlen($this->first_field) < 4 ) { 
                //$error_message = \'Too short!\';
                //return false;
                
                return WP_Error(\'first_field_length\', \'Too short. At least 4 characters is required.\' );
            }
        }
                    
        function save_to_db() {         
            if ( !$this->form_validation() ) {
                ?>                   
                    <script language="javascript">$("#message_label").text("<?php echo $this->form_validation()->get_error_message(); ?>"); $(\'#messages_box\').dialog();</script>
                <?php
            } else {    
            }
        }
                    
        function show_custom_form() {
            ob_start():
            
            if (isset($_POST[\'post_form\'])) {
                $this->save_to_db();
            }
            
            $this->show_template_form();
            
            return ob_get_clean();
        }
}

然后它会传递消息，但要看到对话框出现，它会在entry\\u content的layout div之后的版面上显示消息，此时它应该传递到dialog的div template消息框中。。。。这就是为什么我尝试传递一个变量。。。

        function form_validation() {
...
                $error_message = \'Too short!\';
...
        }

        function save_to_db() {         
...           
                    ... echo $error_message;...
        }

if ( strlen($this->first_field) < 4 ) {