Understanding Hook

In Drupal documentation, HOOK is a key word shown everywhere.

For example, we can see this hook_preprocess_HOOK. The first hook is like the module name you put this function in. The second HOOK with capital case has special meaning. It means the #trigger#, it can be a theme name or panel/ block/ view instance name.This function will be excuted when the hook is enabled and HOOK is going to be rendered in the page.

hook is like Laravel’s container, while HOOK is the services. hook_preprocess_theme -> template hook_preprocess_block

Creating Hook

Drupal’s hook system is the way let modules interact with each other.

At first, define a hook in the host module (automatically it will be called in place):

  // Let's say the name of module to define the hook is "host_module"
  // Sample 1, intercepting hook
  $result = array();
  foreach (module_implements('hook_name_1') as $module) {
    // Calling all modules implementing hook_hook_name_1 and 
    // Returning results than pushing them into the $result array:
    $result[] = module_invoke($module, 'hook_name');
  }

   // Sample 2, alter hook
   $data = array(
     'key1' => 'value1',
     'key2' => 'value2',
   );
   
   // Calling all modules implementing hook_my_data_alter():
   drupal_alter('hook_name_2', $data);

And then implement hook in other modules

// The name of module to implement the hook is "other_module".
// Here we try to modify the variables in "host_module".
function other_module_host_module_hook_name_1() {
  //Implementation code goes here
}

function other_module_host_module_hook_name_2_alter() {
  //Implementation code goes here
}

preprocess theme hook

This is a reference about the sequence of running pre-process hook.

When we using a preprocessor without specify a theme hook, a second parameter could be passed as current hook.

function sample_module_preprocess(&$variables, $hook) {
  // Use the theme hook name to set the base class, used for BEM modifiers.
  $varaibles['base_class'] = drupal_html_class($hook);
}

hook_menu

This is the router of Drupal, link the url and callback function together, please note the Drupal bootstrap will be called.

Theme Hook

  • <module_name>_theme: This is the place to store theme registration, also you could define how the theme will be rendered.
function sample_module_theme() {
 $return = array(
   // This theme will be called by theme() and 
   // variables will be casted into the template.
   'sample_theme_name_1' => array(
     'variables' => array?
       //variables go here!
     ),
     'template' => 'template_name',
     'path' => '/path/to/template'
     'preprocess functions' => $preprocess_functions,
   ),
   // return a rendered element tree
   'sample_theme_name_2' => array(
     'render element' => 'element'
   ),
 );
}
  • theme_<theme_name>($variable): After is registered above, this default function will be provided to implement (return html markup).
// sample_theme_name_1 don't need this.
function theme_sample_theme_name_2 {
  return render($render_array);
}

  • theme() function: Route it to either the template file or theme function.

  • <module_name>_preprocess_<theme_name> / hook_preproces_HOOK Please refer the preprocess hook above.

hook for Node/ Field/ View

  • hook_preprocess_node, hook_preprocess_field, hook_preprocess_view

We need these hooks when we would like to set the themes_hook_suggestion or pass the variables to the template like node__<content_type>__<teaser>.tpl.php.

##Field Type API##

This is the field type API DOC

  • hook_field_info: define the name, description, formatter and widget.

Form Hook

  • hook_form

  • hook_form_alter: update the render array before form is rendered.

  • TBC

Panel Hook

hook_panel_pane_prerender($pane) hook_panel_pane_content_alter(&$variable, $pane)

Block Hook

  • hook_block_info(): define the block’s name.
$block_default = ['cache' => DRUPAL_NO_CACHE, 'category' => t('Sample Category')];
$blocks['sample_block'] = array_merge($block_default, [
    'info' => t('Sample Block'),
  ]);
return $blocks;
  • hook_block_view(): define the block’s render array.
function sample_module_block_view($delta) {
  $block = array();
  $block['content']['#theme'] = $delta;
  return $block;
}
  • hook_preprocess_block(): modify the variable before the block get rendered.

View Hook

  • hook_preprocess_view

  • template system: @todo

Page Hook

  • hook_preprocess_page

  • TBC

hook_library

hook_library will register the library, but it will not add this library automatically. so the following code is needed:

form['#attach']['library'][]=library('module_name', 'library_name');

Ajax framework

The drupal provide the Ajax form out of box, this is an example to show how to use it.

// #ajax is the indicator that when this field is changed, 
// a callback on server side will be triggered in AJAX way.
// wrapper is the CSS ID of the area to be replaced by AJAX callback. 
function ajax_example_simplest($form, &$form_state) {
  $form = array();
  $form['changethis'] = array(
    '#type' => 'select',
    '#options' => array(
      'one' => 'one',
      'two' => 'two',
      'three' => 'three',
    ),
    '#ajax' => array(
      'callback' => 'ajax_example_simplest_callback',
      'wrapper' => 'replace_textfield_div',
     ),
  );