How do I get a list of Drupal 7 active contexts for the current page/form in hook_form_alter?

Question

I have several contexts defined for my site. In hook_form_alter I need to find out which of them are active. I am trying to use context_active_contexts, but that is only showing 2 of the (at least) 3 that are active. i.e. I have contexts A, B and C. C has a block reaction and the block is visible. My code only outputs A and B. If I disable C, the block disappears from the output, giving me some confidence that it really is context C that is responsible for it. Why can I not see A, B and C in the output?

function MyModule_get_current_location_contexts() {
  $contexts = context_active_contexts();

  $locations = array();
  foreach ($contexts as $context) {
    $locations[$context->name] = $context;
  }

  return $locations;
}

function MyModule_form_alter(&$form, &$form_state, $form_id){
  dsm('Contexts (form):');
  if ($form_id == 'MyForm') {
    $contexts = MyModule_get_current_location_contexts();

    foreach ($contexts as $context) {
      dsm($context->name);
    }

    dsm($form);
  }
}

function MyModule_node_view($node, $view_mode, $langcode) {
  dsm('Contexts (entity):');
  $contexts = MyModule_get_current_location_contexts();

  foreach ($contexts as $context) {
    dsm($context->name);
  }
}

Answer 1

The context name is the array key, not it's ->name field. See my answer here on how to programmatically check if a context is active.

No need for foreach loop on $contexts on the 2nd and 3rd functions. Instead of loopoing on $contexts and printing for each context it's name field, you should simply print the array keys:

print_r (array_keys($contexts));

Answer 2

I believe the cause is that your form alter function is firing before the node conditions are met, so the context isn't active until a little later on in the Drupal loading.

One solution is to attach an #after_build callback in your form alter, to can check the active context properly.

function example_form_alter(&$form, &$form_state, $form_id) {
  $form['#after_build'][] = 'example_form_alter_node_after_build';
}

function example_form_alter_node_after_build($form, &$form_state) {
  // Check active contexts here
}