[Drupal] How to implement hook_theme in your custom Drupal 7 module?

The purpose of implementing hook_theme either in a custom module or theme is to register it's theme implementations which specify how a particular render array is to be rendered as HTML.

First of all, if you want to implement hook_theme in your custom Drupal 7 module, you would require to create a custom module. Read on how to create a custom module in Drupal 7 here. Now, you can implement the hook_theme in your '.module' file. Here is the code:

<?php
/**
 * Implements hook_theme().
 */
function CUSTOMMODULE_theme($existing, $type, $theme, $path) {
  $custom_theme = array();
  $custom_theme['comment_admin_overview'] = array(
    'render element' => 'form',
    
    // example theme template register
    // for sites/all/modules/custommodule/templates/comment_admin_overview.tpl.php
    'template' => 'comment-admin-overview',
    'path' => drupal_get_path('module', 'custommodule') . '/templates',
  );
  
  return $custom_theme;
}
?>

Above, the custom theme function is passed an array of associative elements and it get registered in the theme registry. A theme function or template is created when we implement hook_theme(). Using the theme function or template, we can print the variables prepared in the preprocess function, to the screen. Also, we can wrap the variables with any desired HTML. For this we need to add a custom theme function or a custom template file. Further we can define a preprocess function to prepare the variables for the theme function or template.

For more help to theme a Drupal 7 form using custom module, please contact us.