Submission handler for the user registration form doesn't work

Question

I'm working on a Drupal 7 portal. I added a custom field to the registration form and I would like to get hold of custom field value when the registration form is submitted and before it is stored in the database.

I'm trying to use the submission handler for the registration form and print the content of $form and $form_state, but those values never get printed as message. I installed the Devel module as well.

function user_register_form_submit($form, &$form_state) {
    drupal_set_message('<pre>'. print_r($form, 1) .'</pre>');
    drupal_set_message('<pre>'. print_r($form_state, 1) .'</pre>'); 
    drupal_set_message(t('An info message from user_register_form_submit'), 'error');
}

I appreciate any input on what the issue could be.

Answer 1

In hook_form_alter use foloowing code

function MODULENAME_form_alter(&$form, $form_state, $form_id) {
if($form_id == 'user_register_form'){
    $form['#submit'][] = 'module_custom_form_submit';
   }
}

after that use

function module_custom_form_submit($form, &$form_state) {
    // Do whatever you want.
}

Answer 2

There are two issues in the shown code.

1. Simply defining a function is not sufficient for Drupal to consider it a form submission handler, not even if the function name ends with _form_submit. To add a new form submission handler, the module you are developing needs to implement hook_form_alter() or hook_form_FORM_ID_alter(), and add a new form submission handler.

   function mymodule_form_user_register_form_alter(&$form, &$form_state) {
     $form['#submit'][] = 'mymodule_user_register_submit';
   }
   

2. To debug a form submission handler you should use watchdog(). Once the Database logging module is installed, on admin/reports/dblog you can read all the messages added with watchdog().