drupal - add select/option list to a form

Question

I am a bit confused. I have created a simple form with a one text box and a submit button. Now I want to add a select/option dropdown box of taxonomy terms, using the taxonomy_get_vocabularies() function.

 $vocabularies = taxonomy_get_vocabularies('my_type'); 

My question is how do I get vocabulary list onto form "the Drupal way". The way Drupal defines form seem quite rigid. Also how could I make this conditionl, say on existence of relevant taxonomy terms.

function my_form_name($form_state) {

// A Short question.
  $form['title'] = array(
    '#type' => 'textfield',
    '#title' => t('Question'),
    '#default_value' => $node->title,
    '#required' => TRUE,
    '#weight' => 1,
    '#description' => t('A text box goes here '),   
  );

  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => t('submit'),
    '#weight' => 7,
  );

  return $form;

Answer 1

I'm doing something similar in a custom form, and found it much easier to use taxonomy_get_tree, with the vocabulary code as the function's argument. See below:

//get the list of locations from taxonomy to use in the dropdown
$dropdown_source = taxonomy_get_tree(2);
$dropdown_array = array('0' => '--none--');
foreach ($dropdown_source as $item) {
$key = $item->tid;
$value = $item->name;
$dropdown_array[$key] = $value;
}

//location filter dropdown
$form['filterset']['locationfilter'] = array(
  '#weight' => '1',
  '#key_type' => 'associative',
  '#multiple_toggle' => '1',
  '#type' => 'select',
  '#options' => $dropdown_array,
  '#title' => 'Filter by location',
);

unset($dropdown_array);