Display the Form

drupal_get_form($form_id)


Form Callbacks

There has 3 callbacks: form callback, validate callback, submit callback.

xxx_form($form_state)
xxx_form_validate($form, &$form_state)
xxx_form_submit($form, &$form_state)


Form theme: theme_xxx_form($form)
Functions can be used in form theme:

drupal_render(&$elements)

Example:

$output .= drupal_render($form['name']);
……
$output .= drupal_render($form);


Hooks

hook_forms()
This hook is for map form_ids to builder functions.

hook_form_alter(&$form, $form_state, $form_id)
This hook allow any form (even those in core) can be altered in almost any way imaginable–elements can be removed, added, and rearranged