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Adding custom fields to core components using a plugin

From Joomla! Documentation

Have you ever wished that there was an extra phone number field in com_contact or needed an extra field for articles in com_content? Joomla provides a straight-foward way of integrating new fields with core components such as these. All it takes to achieve this is a simple content plugin and a layout override in your template.

This article shows how to add an extra field to a core component using the example of adding an additional email address to contacts in com_contact.

Adding a custom field

It is recommended that you first read Creating a Plugin for Joomla for details on how to create and install a plugin, which is not covered here.

To add a field to a system component you need to create a content plugin which picks up the onContentPrepareForm event and inserts it's own fields into the given JForm. The following code is for Joomla 3.1 and later, for Joomla 2.5 the language files need to be loaded in the constructor (see J2.5:Creating a Plugin for Joomla).

<?php
// no direct access
defined ( '_JEXEC' ) or die ( 'Restricted access' );
 
class plgContentExample extends JPlugin {
 
        /**
         * Load the language file on instantiation.
         * Note this is only available in Joomla 3.1 and higher.
         * If you want to support 3.0 series you must override the constructor
         *
         * @var boolean
         * @since 3.1
         */
 
        protected $autoloadLanguage = true;
 
        function onContentPrepareForm($form, $data) {
                $app = JFactory::getApplication();
                $option = $app->input->get('option');
 
                switch($option) {
 
                        case 'com_contact':
                                if ($app->isAdmin()) {
                                        JForm::addFormPath(__DIR__ . '/forms');
                                        $form->loadFile('contact', false);
                                }
                                return true;
 
                }
                return true;
        }
 
}
?>

The additional fields are loaded from the file forms/contact.xml in the plugin directory. It's important that these fields are in a fields element with the name property set to "params". If you don't set this property name the fields will appear in the admin site but the values will not be saved.

In this case we are adding a field for a label to describe the email field in the public website and a second field for the value of the email address.

<?xml version="1.0" encoding="UTF-8"?>
<form>
        <fields name="params" >
                <fieldset name="params" >
                        <field
                                name="contact_emaillabel2"
                                type="text"
                                label="PLG_CONTENT_EXAMPLE_CONTACT_EMAILLABEL2"
                                />
                        <field
                                name="contact_email2"
                                type="text"
                                label="PLG_CONTENT_EXAMPLE_CONTACT_EMAIL2"
                                filter="email"
                        />
                </fieldset>
        </fields>
</form>

Finally we need a language file so that the parameters are presnted nicely in the admin site and are translatable into different languages. This file needs to be called something like en-GB.plg_content_example.ini.

COM_CONTACT_PARAMS_FIELDSET_LABEL="Additional Information"
PLG_CONTENT_EXAMPLE_CONTACT_EMAIL2="Additional email address"
PLG_CONTENT_EXAMPLE_CONTACT_EMAILLABEL2="Additional email label"

That's it for adding the field to com_contact. If you install this plugin you'll have an additional tab in the contact editing form called "Additional Information" with the new fields included. If you fill in the new label and an email address fields for a contact you'll see that com_contact will store and retrieve the information for you.

The same plugin can be used to add more fields to different components, just add the relevant code into the onContentPrepareForm function and create the appropriate XML form files.

Displaying the custom field

To display the custom field you need to create a layout override for the relevant component in your template. For more details on creating templates see Creating a basic Joomla! template, for details on layout overrides see Understanding Output Overrides.

Copy the file <Joomla>/components/com_contact/views/contact/tmpl/default.php to <template>/html/com_contact/contact/default.php, creating the folders in your template as necessary. We're going to edit this file to include the additional information. The com_contact component will automatically load the additional fields for us and load it into a variable called $thiis->params. All we need to do is check that the data is set and, if so, display it.

To display the field, find the location in <template>/html/com_contact/contact/default.php that corresponds to where you'd like the additional email address to be displayed and add the following code

<?php if ($this->params->get('contact_emaillabel2', false)) : ?>
        <div>
                <span class="contact-additionalemail"><?php echo $this->params->get('contact_emaillabel2');?>:&emsp;<a href="mailto:<?php echo $this->params->get('contact_email2'); ?>"><?php echo $this->params->get('contact_email2'); ?></a><br/></span>
        </div>
<?php endif; ?>

If you add this code and install your template you will now have the custom field displaying in your public website.