Hooks in Joomla

If you're starting out with CiviCRM and Joomla! you might want to check the Joomla guide for creating a plugin.

Once created plugins may be packaged and installed with the Joomla installer or the files can be placed in the appropriate folder and installed with the discover method.

You can implement your hooks using a single hooks file, or by creating a Joomla plugin. In general, implementing through a plugin is preferred as you can benefit from the native access control within the plugin structure, include code that responds to other Joomla events, organize your hook implementations into multiple plugins which may be enabled/disabled as desired, and roughly follow the event-observer pattern intended by Joomla plugins.

Single File Implementation

To implement hooks with a single file, you will do the following:

1. If you have not done so already, create a new directory on your server to store your PHP override files. In Joomla, that is commonly placed in the media folder, as it will not be impacted by Joomla and CiviCRM upgrades. For example, you might create the following folder: /var/www/media/civicrm/customphp.
2. If you have not done so already, configure your system to reference the folder you've created as your override directory. Go to: CiviCRM Administer > Global Settings > Directories. Change the value of Custom PHP Path Directory to the absolute path for the new directory (e.g., "/var/www/media/civicrm/customphp" if you used that suggestion in the earlier step). The custom override directory may also be used to store modified copies of core files -- thus overriding them. You may want to familiarize yourself with its purpose if you are not yet.
3. Create a file named civicrmHooks.php to contain your hook implementations, and upload the file to the directory you just created.
4. Within that file, your hooks will be implemented by calling the hook function prefaced by "joomla_". For example, you would call the buildForm hook (used to modify form rendering and functionality) by adding the following function to your hook file:

function joomla_civicrm_buildForm( $formName, &$form ) {
    //your custom code
}

Plugin Implementation

If you are implementing hooks with a Joomla plugin, you will create a standard, installable plugin package. At a minimum, a plugin extension will consist of an xml file (defining the plugin and its parameters), and a php file. Within the php file, define a class that extends the Joomla JPlugin class, and call your hooks but adding the appropriate functions. For example, your plugin file may look like the following:

defined('_JEXEC') or die;
jimport('joomla.plugin.plugin');

class plgCiviCRMMyPlugin extends JPlugin {
    public function civicrm_tabs(&$tabs, $contactID) {
        //your code to alter the contact summary tabs
    }
}

The first two lines are required -- the first is for security purposes, and ensures the code will exit if it has not been called from within Joomla. The second includes the necessary parent plugin class.

Joomla plugin classes follow standard naming conventions which you should follow. By naming this plugin class "plgCiviCRMMyPlugin," I am stating that the plugin resides in the plugin/civicrm/ folder, and the plugin file is named "myplugin.php."

For more information about implementing hooks through plugins, see this blog article

Note the reference in the comments to a sample plugin which you can download and modify.

Sample Joomla Plugin With Hooks

This is a simple example of a plugin for Joomla that implements CiviCRM hooks. It consists of two file tabs.php and tabs.xml along with the blank index.html file which is considered good Joomla coding practice.

Note: Somewhere around Joomla 2.5.20 the JPlugin class was moved to cms .plugin.plugin from joomla.plugin.plugin (see the jimport call in Tab.php below). If you have not remained current with the latest Joomla revision, you may need to reference the correct location. If you find your plugins fail after updating to the latest release, be sure to check and fix that reference (it will often fail silently).

Tabs.php

<?php
/**
 * @version
 * @package     Civicrm
 * @subpackage  Joomla Plugin
 * @copyright   Copyright (C) 2005 - 2011 Open Source Matters, Inc. All rights reserved.
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */

// No direct access
defined('_JEXEC') or die;

jimport('cms.plugin.plugin');
class plgCivicrmTabs extends JPlugin
{

/**
 * Example Civicrm Plugin
 *
 * @package     Civicrm
 * @subpackage  Joomla plugins
 * @since       1.5
 */
    public function civicrm_tabs(&$tabs, $contactID)
    {

    // unset the contribition tab, i.e. remove it from the page
    unset( $tabs[1] );

    // let's add a new "contribution" tab with a different name and put it last
    // this is just a demo, in the real world, you would create a url which would
    // return an html snippet etc.
    $url = CRM_Utils_System::url( 'civicrm/contact/view/contribution',
                                  "reset=1&snippet=1&force=1&cid=$contactID" );
    $tabs[] = array( 'id'    => 'mySupercoolTab',
                     'url'   => $url,
                     'title' => 'Contribution Tab Renamed',
                     'weight' => 300 );
    }
}

Tabs.xml

<?xml version="1.0" encoding="UTF-8"?>
<extension version="1.6" type="plugin" group="civicrm">
    <name>plg_civcrm_tabs</name>
    <author>Joomla! Project</author>
    <creationDate>November 2005</creationDate>
    <copyright>Copyright (C) 2005 - 2011 Open Source Matters. All rights reserved.</copyright>
    <license>GNU General Public License version 2 or later; see LICENSE.txt</license>
    <authorEmail>admin@joomla.org</authorEmail>
    <authorUrl>www.joomla.org</authorUrl>
    <version>1.6.0</version>
    <description>PLG_CIVICRM_TABS_XML_DESCRIPTION</description>
    <files>
        <filename plugin="tabs">tabs.php</filename>
        <filename>index.html</filename>
    </files>
    <config>
    </config>
    </extension>

You can make plugins that include multiple hooks or you can make separate plugins. What is appropriate will depend on the application.