Form alter help on drupal

To implement hook_form_alter, simply create a function called 

modulename_form_alter, using the parameters shown. Drupal will 

automatically use this function if it exists in your module.

function mysite_form_alter(&$form, &$form_state, $form_id) {
  // print $form_id;
  switch ($form_id) {
    case 'blog_node_form':
      // remove some unwanted node editing fields
      $form['revision_information']['#access'] = 0;
      $form['menu']['#access'] = 0;
      $form['author']['#access'] = 0;
      // override node options permissions defined by 'administer nodes'
      $form['options']['#access'] = 1;
      $form['options']['status']['#access'] = 1;
      $form['options']['promote']['#access'] = 0;
      $form['options']['sticky']['#access'] = 0;
    break;
    case 'page_node_form':
      // don't ever allow page nodes to be promoted or sticky
      $form['options']['promote']['#access'] = 0;
      $form['options']['sticky']['#access'] = 0;
    break;
  }
}

 //

$form['field_teacher']['#default_value']= Array (0 => Array ( 'uid' => 15));

$form['field_teacher'][0]['#default_value']['uid']= $form['uid']['#value'];

1) hook_form_FORM_ID_alter()

2) hook_form_alter()

3) hook_form_FORM_ID_post_alter()

if($form_id='author_node_form') {
        $form['author']=NULL;
        $form['taxonomy']=NULL;
        $form['options']=NULL;
        $form['menu']=NULL;
        $form['comment_settings']=NULL;
        $form['files']=NULL;
        $form['revision_information']=NULL;
        $form['attachments']=NULL;
        if($form["HIDEPREVIEW"]) {
          $form['buttons']['preview']=NULL;
          $form['buttons']['delete']=NULL;
        }

 ****

<?phpfunction genpass_form_alter(&$form, $form_state, $form_id) {
 
  switch($form_id) {
 
    case 'user_admin_settings':
   
      $form['registration']['genpass_mode'] = array(
        '#type' => 'radios',
       .....
      $form['#validate'][] = 'genpass_user_admin_settings_validate';
      $form['#submit'][] = 'genpass_user_admin_settings_submit';
      break;
     
    case 'myaddaleader_form':
    case 'myaddamember_form':
    case 'user_register':
      $pass_item =& genpass_get_pass_item($form);
      // alter the user-admin register (no mode decision)
      if ($form['destination']['#value'] == 'admin/user/user/create' && user_access('administer users')) {
        $pass_item['#required'] = FALSE;
       ....   ?>

mymodule (yes, I called it mymodule)

<?phpfunction mymodule_form_alter (&$form, &$form_state, $form_id) {

  switch ($form_id) {
    case 'group_node_form':
      //    Set the value to what is desired
      $form['og_description']['#default_value'] = "a group";
      // Hide the form item, leave this at the above value
      $form['og_description']['#access'] = 0;
      break;
    case 'user_register':
      // use dpm to see the form array
      return dpm($form);
      break;
    case 'myaddamember_form':// this next bit is cut and paste from content profile module
      require_once drupal_get_path('module', 'node') .'/node.pages.inc';

      // Allow other modules to customize the used profile types, so modules
      // can easily customize the registration form.
      $default_types = content_profile_get_types('names', (arg(0) == 'admin' ? 'admin_user_create_use' : 'registration_use'));
      $form += array('#content_profile_registration_use_types' => $default_types);

      foreach ($form['#content_profile_registration_use_types'] as $type => $typename) {
        content_profile_registration_add_profile_form($type, $form, $form_state);
      }// end the bit cut and paste from the content profile module

      genpass_form_alter($form, $form_state, $form_id);

      $form['account']['notify']['#default_value'] = TRUE;

      $form['account']['pass']['#access'] = FALSE;
      $form['account']['status']['#access'] = FALSE;
      $form['revision_information']['#access'] = FALSE;
      $form['comment_settings']['#access'] = FALSE;
      $form['locale']['#access'] = FALSE;
      $form['path']['#access'] = FALSE;
      $form['print']['#access'] = FALSE;
      $form['book']['#access'] = FALSE;
      $form['menu']['#access'] = FALSE;
      $form['group_phone']['field_phone_privacy']['#access'] = FALSE;
      $form['group_email']['#access'] = FALSE;
      $form['group_homeaddress']['field_homeaddress_privacy']['#access'] = FALSE;
      $form['group_homeaddress']['field_homeaddress_public']['#access'] = FALSE;
      $form['group_homeaddress']['field_homeaddress_leaderviewable']['#access'] = FALSE;
      $form['group_homeaddress']['field_homeaddress_adminview']['#access'] = FALSE;
      break;
    case 'myaddaleader_form':// this next bit is cut and paste from content profile module
      require_once drupal_get_path('module', 'node') .'/node.pages.inc';

      // Allow other modules to customize the used profile types, so modules
      // can easily customize the registration form.
      $default_types = content_profile_get_types('names', (arg(0) == 'admin' ? 'admin_user_create_use' : 'registration_use'));
      $form += array('#content_profile_registration_use_types' => $default_types);

      foreach ($form['#content_profile_registration_use_types'] as $type => $typename) {
        content_profile_registration_add_profile_form($type, $form, $form_state);
      }// end the bit cut and paste from the content profile module

      genpass_form_alter($form, $form_state, $form_id);

      $form['account']['notify']['#default_value'] = TRUE;

      $form['account']['pass']['#access'] = FALSE;
      $form['account']['status']['#access'] = FALSE;
      $form['revision_information']['#access'] = FALSE;
      $form['comment_settings']['#access'] = FALSE;
      $form['locale']['#access'] = FALSE;
      $form['path']['#access'] = FALSE;
      $form['print']['#access'] = FALSE;
      $form['book']['#access'] = FALSE;
      $form['menu']['#access'] = FALSE;
      $form['group_homeaddress']['field_homeaddress_public']['#access'] = FALSE;
      $form['group_homeaddress']['field_homeaddress_leaderviewable']['#access'] = FALSE;
      $form['group_homeaddress']['field_homeaddress_adminview']['#access'] = FALSE;

      // use dpm to see the form array
      return dpm($form);
      break;
  }
}

function myaddamember_form($form_state)
{
  $form=array();
  // Merge in the default user edit fields.
  $form = array_merge($form, user_register($form_state, NULL, NULL, TRUE));
// add this role as default, already checked the checkbox
  $form['account']['roles']['4'] = array(
    '#type' => checkbox,
    '#title' => 'Member',
    '#default_value' => TRUE,
  );
// remove a bunch of roles by setting the allowed options to just these
  $form['account']['roles']['#options']= array(
    '4' => 'Member',
    '5' => 'Leader Applicant',
  );
// make submitting the form actually create a user
  $form['#submit'][] = 'user_register_submit';

  return $form;
}

function myaddaleader_form($form_state)
{
  $myoptions = array('1' => t('Enabled'), '0' => t('Disabled'));
  $form=array();
/*
// test helloworld type form building. keeping during testing to remind me how to do this.
  $form['addaleader'] = array(
    '#type' => 'fieldset',
    '#title' => t('Leader account settings'),
    '#tree' => TRUE,
  );
  $form['addaleader']['thefirstoption'] = array(
    '#type' => 'radios',
    '#title' => t('First Option'),
    '#default_value' => variable_get('thefirstoption', 0),
    '#options' => $myoptions,
    '#description' => t('The First Option.'),
  );
// end test helloworld type form building
*/

  // Merge in the default user edit fields.
  $form = array_merge($form, user_register($form_state, NULL, NULL, TRUE));

  // check some roles by default
  $form['account']['roles']['3'] = array(
    '#type' => checkbox,
    '#title' => 'Leader',
    '#default_value' => TRUE,
  );

  $form['account']['roles']['4'] = array(
    '#type' => checkbox,
    '#title' => 'Member',
    '#default_value' => TRUE,
  );
// keeping to remind me how
//  $form['hidden'] = array('#type' => 'value', '#value' => 'is_it_here');
//  $form['submit'] = array('#type' => 'submit', '#value' => t('Save'));

// make submitting the form actually create a user
//  $form['#validate'][] = 'user_register_validate';
  $form['#submit'][] = 'user_register_submit';

  return $form;
}

function mymodule_menu() {
  $items = array();
// make two new tabs, showing the new create user forms, parallel to the system default add user form
  $items['admin/user/user/createusermember'] = array(
    'title' => 'Add user (a Member)',
    'description' => 'Create a user account for a Member.',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('myaddamember_form'),
    'access arguments' => array('administer users'),
    'type' => MENU_LOCAL_TASK,
  );

  $items['admin/user/user/createuserleader'] = array(
    'title' => 'Add user (a Leader)',
    'description' => 'Create a user account for a Leader.',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('myaddaleader_form'),
    'access arguments' => array('administer users'),
    'type' => MENU_LOCAL_TASK,
  );

  return $items;
}?>

MYMODULE_node_form_submit() is not documented so why this code invoke it?

+  // This form uses button-level submit handlers only, which manually invoke
+  // node_form_submit_build_node(), which in turn executes any form-level submit
+  // handlers prior to invoking node_submit(). For programmatically defined node
+  // types, a TYPE_node_form_submit() handler is therefore expected to be
+  // invoked, if it exists.
+  $form['#validate'][] = 'node_form_validate';
+  $form['#submit'] = array();
+  if (function_exists($node->type . '_node_form_submit')) {
+    $form['#submit'][] = $node->type . '_node_form_submit';
+  }