title: Field Validation and displaying error in wordpress custom post type
body: <p>Hello guys i started my first plugin in wordpress after few work i got struck in field validation.. </p>
  
  <p>Problem is i have a field called <code>"preix_author_url"</code> then in my plugin i use </p>
  
  <pre><code>add_action('save_post', 'my_function_name');
  </code></pre>
  
  <p>i have created a validation class example </p>
  
  <pre><code>&lt;?php
  class validator {
      public static function isUrl($str = '') {
          if(strlen($str) == 0)
              return FALSE;
  
          return preg_match('!^http(s)?://[\w-]+\.[\w-]+(\S+)?$!i',$str);
      }
  }
  </code></pre>
  
  <p>in <code>"my_function_name()"</code> </p>
  
  <pre><code>    function my_function_name(){
              global  $post;
              if(defined('DOING_AUTOSAVE') &amp;&amp; DOING_AUTOSAVE) return;
              if(isset($_POST['post_type']) &amp;&amp; $_POST['post_type'] == 'wallpapers'){
                  require_once( WALLP_FILE_PATH . '/wallp-core/wallp-validator.php' );                
                  $validate = new validator();
                  if(isset($_POST['preix_author_url'])){
                      if($validate-&gt;isUrl($_POST['preix_author_url']))
                          update_post_meta($post-&gt;ID, 'preix_author_url', $_POST['preix_author_url']);
                  }
              }
          }
  </code></pre>
  
  <p>Now i want to show error in post page if validate return false. But i didnt get the way to display those errors or notification.. </p>