Learning Joomla! 3 Extension Development: If you have ideas for additional Joomla 3! features, this book will allow you to realize them. It's a complete practical guide to building and extending plugins, modules, and components. Ideal for professional developers and enthusiasts. , Third Edition

Before we create our first plugin, let's talk about the different types of plugins that you can create for Joomla!. Plugin code is executed when certain events are triggered. You can skip the next couple of pages if you just want to get stuck in with the hands-on example and just go straight to the Where do I start? section, but you may want to refer back to this introduction later when you are creating your own plugins. The different types of plugins are explained as follows:

Each plugin type has its own set of events that trigger these plugins to execute. Each plugin can use one or more event triggers but there is no need to use all the event triggers available, just pick out the ones you need. You also have the freedom to create your own custom plugin event triggers in your components, however, that is also outside the scope of this book. The following table summarizes the types of plugins available and their respective event triggers:

To get started with plugin development, first we need to decide what problem we are trying to solve or what functionality we are trying to implement.

Let's assume that you have a website with various phone numbers listed on the site, and that this site is popular with people who access the site through a smartphone. Currently, to call one of the numbers, the user has to remember the number to dial it, or perhaps they jot it down on a piece of paper or attempt to select and copy the number through their browser. This is not very user-friendly, a much better way to do this would be to change the phone number to a click-to-call link, so the user can just click the phone number and their phone will call it. Now, you could go through the website and manually change all the phone numbers to these links, but that would be inconvenient. Assuming our phone number is in the format 1234-5678, we could change it to this HTML code to create a click-to-call link.

<a href="tel: 1234...

The first file we need to create is the installation XML file (also known as the XML Manifest) which tells Joomla! all about this plugin when you install it through an extension manager. This XML file describes all the files and folders used by this plugin, and what parameters the plugin has. The naming standard of the installation XML file is extensionname.xml, in our case it will be clicktocall.xml as we drop the plg_content_ prefix.

Create a folder called plg_content_clicktocall.

In this folder, create a file called clicktocall.xml and insert the following code:

<?xml version="1.0" encoding="UTF-8"?>
<extension
    version="3.0"
    type="plugin"
    group="content"
    method="upgrade">
  <name>Content - Click To Call</name>
  <author>Tim Plummer</author>
  <creationDate>April 2013</creationDate>
  <copyright>Copyright (C) 2013 Packt Publishing. All rights reserved.</copyright>
  <license&gt...

So now we need to write the PHP file that does all the hard work for this plugin and implements the functionality that we are trying to achieve. In your plg_content_clicktocall folder, create the file clicktocall.php with the following code:

<?php
defined('_JEXEC') or die;

jimport('joomla.plugin.plugin');

class plgContentClicktocall extends JPlugin
{
  function plgContentClicktocall( &$subject, $params )
  {
    parent::__construct( $subject, $params );
  }

  public function onContentPrepare($context, &$row, &$params, $page = 0)
  {
    // Do not run this plugin when the content is being indexed
    if ($context == 'com_finder.indexer')
    {
      return true;
    }

    if (is_object($row))
    {
      return $this->clickToCall($row->text, $params);
    }
    return $this->clickToCall($row, $params);
  }

  protected function clickToCall(&$text, &$params)
  {
    // matches 4 numbers followed by an optional hyphen or space...

Now that you have created all the code for the Click to Call plugin, you need to test it in your Joomla! site to see if it works correctly. We will start out with a way that you might get this running on your development site, then, we will zip it all up into an installable file that you could distribute to other people.

Before we do that, you will need to add some phone numbers in your articles that we are going to turn into Click to Call links, so that we know the plugin works. Add some phone numbers in 1234-5678 or 1234 5768 format.

In your Joomla! 3 development website, find the /plugins/content/ folder and create a new folder clicktocall.

Copy into this folder the files you have created, clicktocall.xml, clicktocall.php, and index.html.

Now in your Joomla! Administrator, navigate to Extensions | Extension Manager, and select the Discover view at the left side. Click on the Discover button and you should see the Content - Click To Call plugin appearing....

Our plugin works well, but what if the phone number format in your country is not 1234-5678? For example, Germany uses the format 123-45678. Wouldn't it be better if we had a parameter where we could set the phone number format? As this is a simple plugin, we are not going to worry about area code prefix or numbers in more complex formats such as 123-456-7890; we are concentrating on numbers that consist of two groups of digits.

We are going to add two parameters to our plugin (also known as options), one that sets the number of digits in the first group, and one that sets the number of digits in the second group.

So open up your clicktocall.xml file, and add in the highlighted code shown as follows (everything between the config tags):

<?xml version="1.0" encoding="UTF-8"?>
<extension
    version="3.0"
    type="plugin"
    group="content"
    method="upgrade">
  <name>Content - Click To Call</name>
  <author>Tim Plummer&lt...

At the moment, all the text used in our plugin is hardcoded, so if a user wanted to change any of the text, they would have to edit the source code which is something we want to avoid for our end users. A lot of people use Joomla! in their native language and not everyone is going to want the text in English. Even if your plugin is only ever going to be used by English speakers, you still want them to be able to easily override the text to suit their needs. So we are going to create a language file, and instead of hardcoding the text, we will use a language string.

Firstly, we are going to replace the text in the parameters we have just added with language strings. Edit the clicktocall.xml file, and make the following changes:

<?xml version="1.0" encoding="UTF-8"?>
<extension
    version="3.0"
    type="plugin"
    group="content"
    method="upgrade">
  <name>Content - Click To Call</name>
  <author>Tim Plummer</author>
  <creationDate...

Congratulations, you have now created your first extension for Joomla!: a plugin to change phone numbers in articles into Click to Call links. We learned about the installation XML file, and the PHP code required to make a simple plugin. We took a look at the different types of plugins in Joomla! and what events can trigger them. We then created an installable package of our plugin and tried it out on a Joomla! website. You can now add Joomla! Extension Developer to your resume!

In the next chapter, you will create your first Joomla! module.