dont understand reference $this in php joomla file

Question

I'm just learning about joomla coding. In http://docs.joomla.org/Developing_a_Model-View-Controller_Component/2.5/Example_of_a_frontend_update_function I see a reference $this->form, see also copied code below.

My beginners question: To what does $this relate?

code site/views/updhelloworld/tmpl/default.php:

<?php
// No direct access to this file
defined('_JEXEC') or die('Restricted access');

JHtml::_('behavior.keepalive');
JHtml::_('behavior.formvalidation');
JHtml::_('behavior.tooltip');

?>
<h2>Update the Hello World greeting</h2>

<form class="form-validate" action="<?php echo JRoute::_('index.php'); ?>" method="post" id="updhelloworld" name="updhelloworld">
            <fieldset>
            <dl>
                <dt><?php echo $this->form->getLabel('id'); ?></dt>
            <dd><?php echo $this->form->getInput('id'); ?></dd>

Answer 1

$this in the Joomla templates (views) is refering to the JView class. The JView class has a lot of standard option which it comes with, and can be found in the documentation you have given. In addition, one can add a view that extends JView so, the method/properties there will be available in the template via $this too.

http://docs.joomla.org/J2.5:Developing_a_MVC_Component/Adding_a_view_to_the_site_part

Following that documentation you can see how the controller renders a view, and how a custom view class can be done.

The exact answer of your question is there too:

This template file will be included by the JView class. Therefore, here, $this refers to the HelloWorldViewHelloWorld class.

Answer 2

$this-> is a context from Joomla.

It is included somewhere, so $this is referenced to the class where the file gets included.

In this, it will be a context of the current page, which is build as a class.