How do I remove a validation handler from a form?

Question

I am using the Invite by e-mail module, which has its own hook_form_alter() with a validation handler. I wish to remove its validation handler and use my own validation handler.

Answer 1

Use hook_form_alter() to change the $form['#validate'] to be your custom validate handler. But if you don't want to run module's validate and submit handler then first unset that specific function from $form['#validate'] and $form['#submit'] array.

function custom_module_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'your_form_id') {
    unset($form['#submit'][array_search('module_submit_handler',$form['#submit'])]);
    unset($form['#submit'][array_search('module_validate_handler',$form['#validate'])]);
    $form['#validate'][] = 'my_custom_validation'; 
    $form['#submit'][] = 'my_custom_submit'; 
  }

}

One more thing to remember please set your custom module weight higher so that your form alter will run after the contrib module.

Answer 2

Use hook_form_alter() to change the $form['#validate'] to be your custom validate handler.

function custom_module_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'your_form_id') {
   $form['#validate'] = array();
   $form['#validate'][] = 'my_custom_validation'; 
  }
}