Custom form field types unavailable in plugin backend when plugin disabled

Question

I've created a plugin and added a couple of custom fields to its backend. For that I followed the indications from the Joomla docs. I extended for example JFormFieldList to get a dropdown list of options.

My fields work fine if the plugin is enabled. But when the plugin is disabled, the list is not rendered. I get just a basic text box.

Same problem with another custom field that should display a button. The button appears if the plugin is enabled but if it’s disabled, I get the same basic text box instead.

I assume therefore that the problem is that the php of the custom fields is not run when the plugin is disabled. Is there a way around that?

EDIT: here’s one of my custom fields

<?php
// Check to ensure this file is included in Joomla!
defined('_JEXEC') or die('Restricted access');
jimport('joomla.form.formfield');
class JFormFieldZotcslLocales extends JFormFieldList
{
    protected $type = 'ZotcslLocales';

    public function getOptions() {
        $path = JPATH_ROOT.'/media/plg_zotbib/locales/*.xml';
        foreach(glob($path) as $file){
            $name = basename($file, '.xml');
            $name = str_replace('locales-', '', $name);
            $locales[$name] = $name;
        }
        return $locales;
    }
}
?>   

And here’s how it’s included in the manifest file

<field name="locale" type="zotcsllocales"
    description="PLG_ZOTBIB_LOCALE_DESC"
    label="PLG_ZOTBIB_LOCALE_LABEL"
    required="true"
    />

Answer 1

The problem was solved by adding a property addfieldpath to the <config> tag of the xml manifest:

<config addfieldpath="/plugins/content/zotbib/fields">

Without this, the custom fields in the backend were only displayed when the plugin was published. When unpublished the corresponding code was not actually run. With this property set the code of the custom fields is always run and they are displayed correctly even if the plugin is unpublished.

The code of my plugin can be seen here: https://framagit.org/svictor/j3-zotbib

Answer 2

@Victor: Obviously, it does not show up since the field definition is part of the plugin, a quick & dirty workaround would be to create a plugin or such wich only serves to show the field type (an empty plugin wich contains the field definition, and since it does nothing else, you can publish it without having other issues). The clean workaround would be to create a field type for each content-type (module, component ecc.) with a different name (since they can be enabled / disabled and a plugin / module / component may not be available in some other parts of the site where you need the field-type)