How to show an error message after publishing a post?

2 comments

1. I wouldn’t use that hook. Here’s why

   Try something like this using admin_notices.

   function wpsites_admin_notice() {
   $screen = get_current_screen();
   if( 'post' == $screen->post_type
   && 'edit' == $screen->base ){
   ?>
   <div class="error">
       <p><?php _e( 'Updated Demo Message!', 'wpsites' ); ?></p>
   </div>
   <?php
   }}
   add_action( 'admin_notices', 'wpsites_admin_notice' );
   

   Untested.

2. add_settings_error(
       'myUniqueIdentifyer',
       esc_attr( 'settings_updated' ),
       $message,
       $type
   );
   

   Check

   http://codex.wordpress.org/Function_Reference/add_settings_error

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