How to add extra tabs inside the banner edit view using a plugin?

Question

I have used the joomla docs to make a hello world plugin and then again the joomla docs to load the plugin within the joomla banners component.

I cant seem to load the extra tabs inside the banner edit view in the admin?

My helloworld.php

<?php
// no direct access
defined('_JEXEC') or die;

class plgContentHelloworld 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_banners':
                if ($app->isAdmin()) {
                    JForm::addFormPath(__DIR__ . '/forms'); // this is the path to the xml file
                    $form->loadFile('bannerfields', false); // this is the xml file
                    echo '<h1>Youre in the banners edit view!</h1>'; // this works
                }
                return true;
        }
        return true;
    }
}

?>

My helloworld.xml

<?xml version="1.0" encoding="utf-8"?>
<extension version="3.0" type="plugin" group="content">
        <name>plg_content_helloworld</name>
        <author>blah</author>
       <creationDate>2012-10-21</creationDate>
        <copyright>blah</copyright>
        <license>GNU General Public License</license>
        <authorEmail>blah</authorEmail>
        <authorUrl>blah</authorUrl>
        <version>1.0</version>
        <description>blah</description>
        <files>
                <filename plugin="helloworld">helloworld.php</filename>
                <filename>index.html</filename>
        </files>
</extension>

forms/bannerfields.xml

<?xml version="1.0" encoding="utf-8"?>
  <form>
   <fields name="params">
        <fieldset name="extrafields" label="Extra content">
            <field name="numero" type="text" size="50" default="" label="Example field" description=""  class="inputbox" labelclass="control-label"  />
        </fieldset>

       <fieldset name="extrafields2" label="Extra content 2">
            <field name="example1" type="text" size="100" default="" label="Example 1" description="" class="inputbox" labelclass="control-label" />
            <field name="example2" type="text" size="100" default="" label="Example 2" description="" class="inputbox" labelclass="control-label" />
            <field name="example3" type="text" size="100" default="" label="Example 3" description="" class="inputbox" labelclass="control-label" />
            <field name="example4" type="text" size="100" default="" label="Example 4" description="" class="inputbox" labelclass="control-label" />
        </fieldset>
  </fields>
</form> 

Thanks in advance :) John

Answer 1

Actually not an answer, but some research shows that: If you rename fields name to attribs like:

<fields name="attribs">

you can add the additional tabs (with fields) in most of the component forms:

• com_templates.style
• com_categories.categorycom_content
• com_categories.categorycom_contact
• com_contact.contact com_menus.item
• etc...

You can add them even in com_categories.categorycom_banners, but this is not the case with com_banners.banner. It is possible to have here bug in Joomla! - see here (though only guess)