Own field type in subform, using with content plugin

Question

for curiosity: I'm using this method to add fields to the standard articles: https://docs.joomla.org/Adding_custom_fields_to_core_components_using_a_plugin/de

I have to use this, since the fields-component does not have subforms, but i prefer this anyway, since i have more control if i write it as plugin.. This has worked great in the last few years, but i have one little issue: When i want to use a custom form field type inside the subform (with the multiple attribute, so that i can create multiple items), i do not know how to set/get the saved value, for instance if i have a select, i have to get the saved value somehow when reopening the article. If it was a single field thats no problem, just get the attributes and get the specific value. But since it is a list, how do i get the current value of that field?

Thanks in advance and best regards

Edit:

The code inside the main form xml:

    <fieldset name="newset" label="New Set">
        <field
            name="person"
            type="subform"
            formsource="plugins/content/cfields/forms/person.xml"
            multiple="true"
            min="1"
            max="99" />
    </fieldset>

The person xml:

<?xml version="1.0" encoding="UTF-8"?>
<form>
    <field
        type="building"
        name="building"
        label="Building person works in" />
    <field
        type="text"
        name="name"
        label="Name" />
</form>

Field code:

<?php
defined('_JEXEC') or die();

jimport('joomla.form.formfield');

class JFormFieldBuilding extends JFormField
{
    protected $type = 'Building';

    private function getBuildings()
    {
        $db = JFactory::getDbo();
        $query = $db->getQuery(true);
        $query->select('*')->from($db->quoteName('#__buildings'));
        $db->setQuery($query);
        $result = $db->loadObjectList();

        return $result;
    }

    public function getInput()
    {
        $rows = $this->getBuildings();
        $return = '<select id="'.htmlspecialchars($this->id, ENT_QUOTES).'" name="'.htmlspecialchars($this->name, ENT_QUOTES).'">';

        foreach($rows as $row)
        {
            $return .= '<option value="'.htmlspecialchars($row->alias, ENT_QUOTES).'">';
            $return .= htmlspecialchars($row->title, ENT_QUOTES);
            $return .= '</option>';
        }

        $return .= '</select>';
        return $return;
    }
}

Since this field will be repeated and saved in the attributes column of the current article, how do i find out the current value?

Answer 1

If you're asking how to mark the value as selected in Building field, compare the list values with current value ($this->value) and add selected attribute when values match:

    foreach($rows as $row)
    {
        $return .= '<option value="'.htmlspecialchars($row->alias, ENT_QUOTES).'"';
        $return .= $this->value == $row->alias ? ' selected>' : '>';
        $return .= htmlspecialchars($row->title, ENT_QUOTES);
        $return .= '</option>';
    }

Or you could extend JFormFieldList instead. It already handles this.

defined('_JEXEC') or die();

jimport('joomla.form.formfieldlist');

class JFormFieldBuilding extends JFormFieldList
{
    protected $type = 'Building';

    public function getOptions()
    {
        $db = JFactory::getDbo();
        $query = $db->getQuery(true)
            ->select(array($db->quoteName('title', 'text'), $db->quoteName('alias', 'value')))
            ->from($db->quoteName('#__buildings'));
        $db->setQuery($query);

        return $db->loadObjectList();
    }
}