How Joomla pieces work together (components, modules, and plugins)

http://docs.joomla.org/How_Joomla_pieces_work_together

talks about Object oriented programming to make components and the stuff that makes things happen in Joomla...

How Joomla pieces work together

Some weeks ago I was asked to confirm if a custom PHP web development with a high budget was the right path to follow. After having a look at the goals of the project I thought that the custom path was overkill and told him that I believed that any open source CMS customization could deliver the same for lot less money. Having made a selection a year or so before I recommended Joomla! as the right tool for the job expecting that my paper will end at this point. But I finally got involved.

The only weak point of Joomla! at the time I made my selection (version 1.x) was that is was slow because of the huge joomla.php library file but I thought when making my recommendation that the new hardware we have now would compensate.

But to my surprise the Joomla! 1.5.2 framework had just been released and a first look at it was promising. The problem was that there is very little, if any information at all about how the pieces that Joomla! connect with each other. After developing a component, a module and a plugin to achieve the goals of the project, I had to look at lots of disparate small documents, source code and tantra to learn how these pieces work together to make the new Joomla! 1.5. It's a fabulous environment to develop web solutions in an easy and powerful way. My congratulations to the development group that has been able to envision such a magnificent tool.

This document is my attempt to express to the community what I have learned while developing the project and also learn from the feedback and help from others. Because I am quite sure that there are lots of things that need revision I humbly request the help of the Joomla! gurus out there to take the time to read this somehow long dissertation and feed me with their knowledge. And, not less important, I request your tolerance if my English is not Oxford-like because I am not a native English speaking person. Luckily, this is a wiki, and others have come by to help with some editing.

Ok. Let's start...

You enter the Joomla! framework by making calls to index.php. Joomla! is designed mainly to deliver the results of component files. When you call a page link like index.php?option=com_ the Joomla! framework tries to find and load the file components/com_/.php from whatever the folder you have installed Joomla! into. So if your component is 'com_read' you should have a 'com_read' folder and a file named 'read.php' inside of it. I will call this file the 'base file' and it is in this file where you make the decision whether to use an old flat model (returning the HTML code for the requested page) or to use a Model-View-Controller (MVC) pattern.

This MVC model, walks over two legs: a file and a class. The Joomla! framework will usually look for a given file and if found, tries to register a specific class within this file. If either one is missing the call fails.

You start all the fireworks by including a controller file in your base file. The controller file can be named anything you want, but by convention it is called 'controller.php'. In your base file (.php), the following code is typical:

require_once(JPATH_COMPONENT.DS.'controller.php');