display selectable drop down options based on a checkbox selection

Question

I am trying to create a form in Drupal. I want to create the following situation: if a checkbox is selected I want to display a drop down menu. can you please suggest a way to do it.

Answer 1

You can use Drupal form api states.

Example:

function example_form_states($form, &$form_state) {

  $form['click_me'] = array(
    '#type' => 'checkbox',
    '#title' => t('Click me!'),
  );

  $form['example_states'] = array(
    '#type' => 'select',
    '#title' => t('Lorem ipsum dolor sit amet'),
    '#options' => array(
      0 => t('Test 1'),
      1 => t('Test 2'),
     ),
    '#states' => array(
      'visible' => array(
        ':input[name="click_me"]' => array('checked' => TRUE),
      ),
    ),
  );

  return $form;
}

Additional Resources https://api.drupal.org/api/examples/form_example!form_example_states.inc/function/form_example_states_form/7.x-1.x https://api.drupal.org/api/drupal/developer!topics!forms_api_reference.html/7.x#states

Answer 2

Programatic way

  $form['checkbox_form'] = array(
    '#type' => 'checkbox',
    '#title' => t('sometitle'),
    '#default_value' => variable_get('checkbox_form', TRUE),
  );

  $form['selectbox'] = array(
    '#type' => 'select',
    '#title' => t('sometitle'),
    '#default_value' => variable_get('selectbox'),
    '#options' => array(
          TRUE => t('Yes'),
          FALSE => t('No'),
     ),
    '#states' => array(
      'visible' => array(
        ':input[name="checkbox_form"]' => array('checked' => TRUE),
      ),
    ),
  );

Second form element visible makes the trick.

Module Way

Use Conditional Fields module.

Conditional Fields allows you to manage sets of dependencies between fields. When a field is “dependent”, it will only be available for editing and displayed if the state of the “dependee” field matches the right condition. When editing a node (or any other entity type that supports fields, like users and categories), the dependent fields are dynamically modified with the States API. A simple use case would be defining a custom “Article teaser" field that is shown only if a "Has teaser" checkbox is checked, but much more complex options are available.