Plugin API

In Omeka, plugins have access to the functions used by themes as well as the core Omeka software and Zend Framework's functionality. Omeka also provides two additional features for plugin developers: Hooks and Filters.

Hooks

Hooks are the primary ways your plugin can modify the behavior of Omeka. The add_plugin_hook() function contains two arguments:

  1. The name of the hook, which will run at a predefined time during an Omeka process. See below for some often used hooks.
  2. The name of your custom function (called a callback) that will be run at the specified time. It is important to ensure that your callback function is named uniquely, so we recommend prefixing your plugin name to the callback name.
<?php add_plugin_hook('hook_name', 'plugin_name_callback_name'); ?>
<?php add_plugin_hook('install', 'myplugin_installer'); ?>

Filters

Filters are like hooks except they are used to modify existing data in Omeka rather than add new behaviors.

An example of a filter:

add_filter('admin_navigation_main', 'my_plugin_admin_navigation');
function my_plugin_admin_navigation($tabs)
{
  $tabs['Foobar'] = uri('foobar');
  return $tabs;
}

Note a few things from this example: The data to be filtered is always received as the first argument to the callback. That data must then be returned by the function in order for the filter to work properly. In this example, 'admin_navigation_main' is the name of the filter corresponding to the top-level navigation for the admin theme, and $tabs is a predefined array of navigation elements. This example will add a link to the admin navigation with the text 'Foobar', and the URI that is generated will be something like /omeka-site/admin/foobar.